Climate review and Experimental Long Range Forecast for SW England. July 2021.

Published 19 July 2021.

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1. Influences.

Changes in sea temperature

Atlantic sea temperatures are generally warmer than climatology except for the area west from Biscay. The North Sea, Baltic and Med are well above average for the time of year. Tropical Atlantic is near or slightly above average and is forecast to remain warmer than average through the remainder of 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific remain and show similar anomalies to last month. Forecasts suggest that Pacific Sea Surface temperatures may remain in a neutral or slightly negative state through summer and trend towards La Nina after October. The West Pacific, especially near Japan and also the Northern Indian Ocean are well above normal for mid July.

The North Atlantic Oscillation index (500hPa index shown below) has been neutral or slightly positive for much of July but is again forecast to turn negative over the next week or two, although perhaps only briefly. The negative NAO is consistent with a blocked or non mobile pattern which can be anticyclonic or cyclonic over the UK depending on the location of the “blocked” high and low pressure centres. Indications are not strong in either direction.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

Until mid month July was wetter than average in terms of the number of wet days and total rainfall for the whole month with close to average temperatures. For about a week from mid July though there has been a longer dry and very warm spell lifting average temperatures above normal for the month as a whole. Sunshine up to mid month looks to have been below average.

April May June 2021 UK Met provisional Temperature and Rainfall anomalies are shown below and illustrate the potential for extremes. Temperature swings from cold April and May followed by warmer June and Rainfall that deviated markedly from the long term average indicates the unusual times for the UK climate.

UKMO top row Temperature anomalies April to June, lower row Rainfall anomalies April to June.

UK River flows in June 2021 were well below normal except in the wetter South and SouthEast of England . Details can be found in the June 2021 Hydrological summary PDF

River levels on the 17th of July were more or less normal but starting to reduce in places

Reservoir levels, according to SW Water were fairly high across SW England as of 11th July 2021.

Global Flood Awareness (updated to version 3) July forecast for the period July to October indicates slightly above normal flood risk for SW England. Blue above normal flood risk, White (river in grey) normal and Orange below normal.

Rainfall during the severe flooding in Germany amounted to at least 100 to 200mm in 24 to 48 hours over a fairly widespread area following an already wet period. Forecast models suggest 100mm totals a few days before the event and the river flow forecast tool suggested river flows in excess of the 1 in 20 year return period but only shortly before the event.

2021 Atlantic hurricane season Started 22 May 2021. Data from Wikipedia.

Wind speeds reaching tropical depression category = 5, storm category = 5, hurricane strength 1. Total fatalities 19. Estimated damage more than 390 million USD.

No current Atlantic tropical storms as of 19th July 2021.

Atmosphere: Predictions.

A: 1: Stratosphere

North polar stratospheric circulation is in “summer” mode as seen by the 10hPa and 50hPa analysis charts for the 16th July 1200UTC.

2: Upper Troposphere

CFSv2 200hPa contours (top row) and CFSv2 anomaly (middle) and NMME (lower row) for August to November 2021 hint at a less mobile patterns across the Atlantic for August and October but more cyclonic patterns near the N of the UK for September and possibly November.

B: Lower Troposphere:

Selection of model solutions for August to October using July 2021 data are shown below. Top row temperature anomaly and lower row precipitation anomaly.

CFSv2 mean of 10 days data to 7th July for August September October

NMME multi model ensemble data to 7th July for August September October

NASA July data for August September October

ECMWF July 2021 data

Data (as supplied to WMO) shown below, top row temperature anomaly and lower row precipitation anomaly. Left image three month mean then individual months.

BoM Australia

Graphics for the Autumn can be viewed in the July data at http://www.weather-info.co.uk/wxsvc/seaslatest.html

Winter December 2021 to February 2022 – limited graphics.

C: Comparing the output of seasonal models for 2021 April May June based on MarchFebruary 2021 data for the UK and Ireland.

For graphics and details see Verification review April May June

Details looked for in seasonal forecast:

Temperature;. for the season the warmer June did not offset the two colder months hence below average for the season but can we see any trend colder then warmer?

Rainfall. Parts of S and SE England were above normal for the season but elsewhere the wet May was mostly offset by the other dry months.

Sunshine above average for the season

Pressure above average for the season (Slack) (April well above, May well below, June above)

Original Summary – Summary – 180321 –
Temperture: There looks to be more models suggesting near normal than typical although the main signal is for above normal with hints that this could occur later in the three months than earlier in the period.
Rainfall: Very mixed indications, possibly near normal overall. Probably some longer drier than average periods, mostly in April and more likely in the south but not a clear signal. For the three months some areas above average perhaps most likely in the north. Pressure possibly a little above average in the south.

Comment: 030721 – Although the season turned out below average the indication for warmer later was correct and the increased number of near normal solutions may have been a pointer to colder values. Reasonable indication for drier April and for some areas above normal but suggestion that this would be the north was wrong. Pressure was slightly above average for the season but not just in the south.
200hPa not enough troughing in May but CFS2 anomaly hinted at lower heights over France than in April or June.

Scoring will attempt to state good, fair, poor or no signal.
THREE MONTH SCORES
1. Russia (WMO): Temp good (model tends to be colder than others). PPN fair .
2. USA – CFS2 : Temp poor . PPN poor .
3. UKMO Contingency: NIL
4. UKMO : Temp poor. PPN poor. PMSL poor
5. USA – IRI : Temp poor. PPN fair.
6. KMA APCC : Temp poor. PPN no signal .
7. JMA : Temp poor. PPN poor. PMSL good
8. NMME : Temp poor. PPN fair .
9. WMO multi : Temp poor. PPN poor.
10. BCC : Temp poor. PPN poor.
11. NASA : Temp poor. PPN poor.
12. Brazil: Temp fair. PPN poor.
13. CanSips : Temp fair trend poor overall. PPN fair overall poor trend.
14. IMME : Temp poor. PPN poor.
15. Copernicus Temp poor. PPN poor. PMSL fair
16. CMCC Temp poor. PPN poor. PMSL good
17: DWD Temp fair. PPN fair. PMSL fair
18. EC Temp fair. PPN fair. PMSL fair
19 JMA Temp poor PPN fair. PMSL fair
20 UKMO Temp poor. PPN poor. PMSL poor
21. MF Temp poor. PPN fair. PMSL good
22 NCEP Temp poor. PPN fair. PMSL good
23 ECMWF (monthly) Temp poor. PPN poor.

2: Forecast.

Remainder of Summer 2021 (August)

Temperature above average most likely.

Rainfall uncertain but a good number of solutions suggest below average rainfall in south UK. This can easily be upset by a few thundery rain events. Hence possibly more dry days than average even if rain totals are higher.

August climate: 1981 to 2010 average daily mean temperature 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset, 13 to 15 Celsius elsewhere. Average 1981 to 2010 rain 40 to 80mm but over the moors, typically 125-150mm.

Autumn 2021 (September October November).

Milder than average but chance that October could be closer to average. Some western parts of the region could also be near average. Wetter than average overall. Rainfall may be below normal in one of the months but no agreement as to which month.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2021 /22 (December January February) limited data.

Milder than average Winter although there might be near average values early in the winter. Rainfall may be below average in January but overall above average rainfall is more likely for the season. Below average snowfall is most likely which mostly limits snow to the Moors.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

Climate review and Experimental Long Range Forecast for SW England. June 2021.

Published 19 June 2021.

1. Influences.

Changes in sea temperature

Atlantic sea temperatures are generally warmer than climatology except for the area centred on 50 deg North 30 deg West. North Sea, Baltic and Med are well above average for the time of year. Tropical Atlantic is slightly above average and is forecast to remain warmer than average through the remainder of 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific remain and show similar anomalies to last month. Forecasts suggest that Pacific Sea Surface temperatures may remain in a neutral state through summer and trend towards La Nina again after October.

The North Atlantic Oscillation index (500hPa index shown below) has been neutral for much of June but is forecast to turn negative over the next week or two. The negative NAO is consistent with a blocked or non mobile pattern which can be anticyclonic or cyclonic over the UK depending on the location of the “blocked” high and low pressure centres.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

Up to the 18th of June temperatures have averaged between 14 and 16 Celsius which is above average for the time of year by about a degree Celsius. June so far has only recorded less than 20% of average rainfall with typical totals ranging between 3 and 15mm. Sunshine so far looks to be a little above average.

The last three months (March April and May 2021) temperature and rainfall anomalies (shown below) illustrate the potential for extremes with an exceptionally dry April followed by an exceptionally wet May – which in places offset each other when looking at the 3 month maps. Temperature swings from mild March followed by a cold April show that it is not just rainfall that deviates from the long term averages..

UKMO temperature anomaly (top row) and rainfall anomaly (lower row)

It was not just the UK that had cold, wet and dull weather in May 2021 – the maps below ( pressure sunshine temperature and rainfall anomalies) show how widespread the event was.

River flows in May 2021 were well below normal. Details can be found in the May 2021 Hydrological summary PDF

River flows currently near average but a few are showing reductions in flow.

Reservoir levels across SW England were fairly high as of 13th June 2021 following the heavy rain in May.

Global Flood Awareness (updated to version 3) June forecast for the period June to September indicates slightly above normal flood risk for SW England. Blue above normal flood risk, White (river in grey) normal and Orange below normal.

Atmosphere: Predictions.

A: 1: Stratosphere

North polar stratospheric circulation is in “summer” mode as seen by the 10hPa and 50hPa analysis charts for the 18th June 1200UTC.

2: Upper Troposphere

CFSv2 200hPa contours (top row) and CFSv2 anomaly (middle) and NMME (lower row) for July to September 2021 hint at a less mobile patterns across the Atlantic for July and August but more cyclonic patterns near the UK for September.

B: Lower Troposphere:

Selection of model solutions for July, August and September using June 2021 data are shown below. Top row temperature anomaly and lower row precipitation anomaly.

CFSv2 mean of 10 days data to 8th June for July August September

NMME mean of 10 days data to 8th June for July August September

Data (as supplied to WMO) shown below, top row temperature anomaly and lower row precipitation anomaly. Left image three month mean then individual months.

Beijing China

Washington USA – caution using newer averaging period in model hence may appear colder.

Graphics for the Autumn can be viewed at http://www.weather-info.co.uk/wxsvc/seaslatest.html

C: Comparing the output of seasonal models for 2021 March April and May based on February 2021 data for the UK and Ireland.

For graphics and details see Verification review March April May

Details looked for in seasonal forecast:

Temperature. Below average. (March was mostly above but April and May below)

Rainfall. Very mixed three three month average some places above others below – see UKMO map – For countries as a whole: Wales above average elsewhere below. UK below average. However will be looking for indications of very dry April and very wet May

Sunshine above average due very sunny April

Pressure. Above normal. The low pressure in May did not offset the higher pressure in earlier months.

Original Summary – 190221 – Temperature: The overall indication for the Spring Season is for above average tempertures with the highest chance being in the S and E and lowest chance in the N and W. March could well see some colder spells with some models suggesting nearer average values. The strongest positive anomaly seems to be in April. Precipitation: Mixed indications suggesting near or above normal for the season across the NW and W in particilar, elsewhere normal locally below. The strongest chance of below normal being in April across the S or SW of the UK and Eire (This could be a problem with showers not being captured at model resolution). Below normal seems to outnumber the above normal solutions by about 2 to 1 but not always in the same areas – but may indicate some longer than normal dry periods are possible.

Comment. Temperature forecast was very poor. Rainfall did better suggesting long dry periods and the three month season turned out ok ‘ish but not convinced that this was more than luck. Did not capture the extreme dry April and extreme wet May. A number of models picked up the dry April ECMWF WMO CMC Brazil NMME NASA and to a limited extent KMA .

Scoring will attempt to state good, fair, poor or no signal, based on three averages.
Comment: A number of models picked up the dry April
1. Russia (WMO): Temp poor. PPN poor Wales fair England elsewhere no signal .
2. USA – CFS2 : Temp poor. PPN fair .
3. UKMO Contingency: Temp poor. PPN fair
4. UKMO : Temp poor. PPN fair PMSL poor
5. USA – IRI : missing
6. KMA APCC : Temp poor. PPN no signal .
7. JMA : Temp poor. PPN poor. PMSL poor
8. NMME : Temp poor. PPN fair.
9. WMO multi : Temp poor. PPN fair.
10. BCC : Temp poor. PPN poor .
11. NASA : Temp poor. PPN fair .
12. Brazil: Temp fair . PPN fair
13. CanSips : Temp poor . PPN poor .
14. IMME : Temp poor. PPN poor .
15. Copernicus Temp poor. PPN poor . PMSL fair
16. CMCC Temp poor. PPN poor . PMSL poor
17: DWD Temp poor. PPN fair. PMSL good
18. EC Temp poor. PPN fair. PMSL good
19 JMA Temp poor. PPN poor . PMSL poor
20 UKMO Temp poor. PPN poor. PMSL poor
21. MF Temp poor . PPN poor. PMSL poor
22 NCEP Temp poor. PPN poor. PMSL poor

2: Forecast.

Remainder of Summer 2021 (July August)

Temperature near or slightly above average for both July and August. Possibly the warmest anomalies could be in August.

Rainfall uncertain but probably above average rain totals overall. July possibly drier than August which is typical but this could be either more wet days OR a few heavy rain events for example thunderstorms.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. July often drier than August.

Autumn 2021 (September October November).

Milder than average but some western parts could be near average. Wetter than average, especially early in the period. Rainfall may be below normal in one of the months some hints at October being the less wet month with near normal values possible.

Winter 2021 /22 (December January February) very limited data.

Milder than average Winter although February could have near average values. Rainfall may be below average in some months but overall above average rainfall is more likely for the season. Below average snowfall is most likely which mostly limits snow to the Moors.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

Climate review and Experimental Long Range Forecast for SW England. May 2021.

Published 18 May 2021.

1. Influences.

Changes in sea temperature

Atlantic sea temperatures are generally warmer than climatology although areas to the North of Scotland and to the SW of England are cooler due to lack of SW to W winds across the Atlantic. The tropical North Atlantic is forecast to remain slightly warmer than average through Summer and Autumn 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific continue to show a weakening La Nina with further warming having occurred in the West Pacific. Forecasts suggest that Pacific Sea Surface temperatures may remain in a weak La Nina or Neutral state through the remainder of 2021.

The North Atlantic Oscillation index (500hPa index shown below) has been negative since early April and is forecast to remain slightly negative or neutral for a short time before becoming uncertain. The negative NAO is constant with a blocked or non mobile pattern which has changes from anticyclonic to a more cyclonic slow moving pattern. This cyclonic pattern may slowly migrate to a more anticyclonic pattern for the UK in a week or so.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

Up to the 18th of May temperatures have averaged around 10 Celsius which is about 2 degree below the May long term average, although temperatures in the second half of May tend to be warmer than the first half. Rainfall has been well above average, perhaps over double the month average in many places due in no small measure to rainfall on the 8th 12th 13th 25th and 16th. Sunshine has also been below average so for in May.

The last three months (February March and April 2021) temperature and rainfall anomalies are dominated by the cold and very dry April, although March was also quite dry, at least in the S and E of the UK. According to the Met Office; April was exceptionally dry, provisionally the UK’s fourth driest April in a series from 1862. It was cold and the number of days of air frost across the UK was the highest in a series since 1960. It was also the sunniest April in a series since 1919.

River flows in April 2021 were well below normal. Details can be found in the April 2021 Hydrological summary PDF

River levels in SW England have since recovered due to the very wet first half of May although the dry March and April may have impacts with regards ground water levels in future months.

Global Flood Awareness (updated) System. May forecast for the period May to August indicates slightly above normal flood risk for SW England. Blue above normal flood risk, White (river in grey) normal and Orange below normal.

Reservoir levels across SW England were fairly high as of 9th May and no doubt are even higher following the heavy rain after this date.

Atmosphere: Predictions.

A: 1: Stratosphere

North polar stratospheric circulation is in “summer” mode as seen by the 10hPa and 50hPa analysis charts for the 17th 1200UTC.

2: Upper Troposphere

CFSv2 200hPa contours (top row) and CFSv2 anomaly (middle) and NMME (lower row) for June to August 2021 hint at a less mobile patterns across the Atlantic for June and July but more cyclonic patterns near the UK for August.

B: Lower Troposphere:

Selection of model solutions for Summer (June July August) using May 2021 data (from the data source) are shown below, top row temperature anomaly and lower row precipitation anomaly. The full set of graphics can be viewed at http://www.weather-info.co.uk/wxsvc/seaslatest.html

CFSv2 mean of 10 days data to 7th May 2021.

Selection of model solutions for summer (June July August) using May 2021 data (as supplied to WMO) are shown below, top row temperature anomaly and lower row precipitation anomaly. Left image three month mean then individual months.

WMO super ensemble using 11 countries data (DWD and Pretoria data missing)

Selection of model solutions for Autumn (September October November) using May 2021 data (from the data source) are shown below, top row temperature anomaly and lower row precipitation anomaly.

C: Comparing the output of seasonal models for 2021 February March and April based on January 2021 data for the UK and Ireland.

For graphics and details see Verification review February March April

Details looked for in seasonal forecast:

Temperature. Three month average below normal due to cold April, except in N Ireland where not cold enough in April to offset milder Feb and March.

Rainfall. Below normal thanks to very dry April and below average March after above average in February.

Sunshine Above average for season and each month except N Ireland (2 months below) and Scotland (1 month below).

Pressure. Above average for season, below average in Feb but above in March and April

\Written Summary – 160121 –
Temperature: For the three months overall the main indication is for above average temperatures or at worst near normal in western areas. Looking at the month to month detail western areas (Ireland, W Scotland, Wales and perhaps SW England, could be nearer normal with a chance of below normal in February and/or March). Precipitation: Three month overall probably normal or above normal but a chance that N Scotland could be below average. Mixed signals in the month to month variation of wetter areas but some agreement that April could be drier than preceding months.
Comment:
Temperature: Seasonal forecast not correct. Very cold April not indicated but NMME and CFS showed lower warm anomalies in April.
Precipitation: Good signal for April being a drier month – NMME, CFS2, Beijing, Brazil and to some extent Moscow, but overall indication of above average was not correct.

Scoring for the three month season will attempt to state good, fair, poor or no signal.

1. Russia : Temp fair . PPN no signal .
2. USA – CFS2 : Temp fair . PPN fair .
3. UKMO Contingency: Temp poor . PPN poor .
4. UKMO : Temp poor. PPN poor. PMSL poor
5. USA – IRI : Temp no signal . PPN no signal.
6. KMA APCC : Temp poor . PPN no signal .
7. JMA : Temp poor . PPN poor . PMSL poor
8. NMME : Temp poor. PPN fair .
9. WMO multi : Temp poor. PPN poor.
10. BCC : Temp poor . PPN good .
11. NASA : Temp poor . PPN fair .
12. Brazil (WMO): Temp poor . PPN fair .
13. CanSips : Temp poor . PPN poor .
14. IMME : Temp poor . PPN poor .
15. Copernicus Temp poor . PPN poor . PMSL poor
16. CMCC Temp poor . PPN poor . PMSL poor
17: DWD Temp poor . PPN poor. PMSL poor
18. ECMWF Temp poor . PPN poor. PMSL poor
19 JMA Temp fair . PPN poor . PMSL poor
20 UKMO Temp poor. PPN poor. PMSL poor
21. MF Temp poor . PPN poor . PMSL fair
22 NCEP Temp poor. PPN poor . PMSL poor
23 ECMWF (monthly) Temp: no signal. PPN fair

2: Forecast.

Summer 2021 (June July August)

Temperature near or slightly above average for the season. August possibly seeing the warmest anomalies and June the lowest. Most solutions suggest a less warm (compared to average) start to summer and warmer end.

Rainfall for the season uncertain but probably above average rain totals overall. The first half of summer may well be drier than average then turning wetter. Higher rain rates are typical of a warming atmosphere but may not imply an increase in the number of days with rain. Some consensus for August to be wetter than average but this could be either more wet days OR a few heavy rain events.

Autumn 2021 (September October November).

Milder than average also wetter especially early in the period. Rainfall may be below normal although at least one of the three months could be wetter although no agreement between the models but more likely September or October than November.

Winter 2021 /22 (December January February) very limited data.

Milder than average Winter although February could be near normal. Rainfall may be below average which implies below average snowfall.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

Review and Experimental Long Range Forecast for SW England. April 2021.

Published 19 April 2021.

1. Influences.

Changes in sea temperature

Atlantic sea temperatures are generally warmer than climatology although areas to the west of Ireland are cooler due to lack of SW to W winds. The colder Northerly types of late have resulted in cooler values in the southern North Sea despite most of the North Sea being warmer than average. The Norwegian Sea, Baltic Sea and the Med are also mostly near or above normal. The tropical North Atlantic is forecast to remain slightly warmer than average through Summer and Autumn 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific show a weakening La Nina with further noticeable warming having occurred in the west. Forecasts suggest that Pacific Sea Surface temperatures may remain in a weak La Nina or Neutral state through the remainder of 2021.

The North Atlantic Oscillation index (500hPa index shown below) has been negative recently (consistent with the blocked pattern and High pressure near the UK) and is forecast to remain slightly negative or neutral for a short time before becoming uncertain.

The positive NAO phase represents a stronger than usual difference in pressure allowing winds from the west to predominate. The position of the jet stream enables stronger and more frequent storms to travel across the Atlantic bringing more frequent milder and wetter weather types for NW Europe which in summer results in cooler temperatures.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

Up to the 18th temperatures averaged out around 7 Celsius which is about 2 degree below average for April and there have been an unusual number of frosty night/mornings. There has been 10% or less of the normal rainfall and probably more sunshine than usual too.

CPC temperature anomaly and rainfall total for 4 to 10th April 2021

Looking back at the last three months temperatures have recovered since the colder January and rainfall has been trending near ,then below average across SW England.

River flows and ground water levels in March 2021 were normal but trending lower across SW England. Details can be found in the March 2021 Hydrological summary PDF

UK based data is available in The Hydrological Outlook which provides an insight into future hydrological conditions across the UK. Detail can be found at http://www.hydoutuk.net/

Global Flood Awareness (updated) System. April forecast for the period April to July indicates slightly above normal flood risk for SW England. Blue above normal flood risk which probably mostly reflects the current ground water levels.

Reservoir levels across SW England were fairly high as of 11th April but trending lower than normal due to the dry first half of April

Atmosphere: Predictions.

A: 1: Stratosphere

North Pole stratospheric temperatures near normal or a little colder than average.

North Pole temperature at 10hPa and 30hPa

Since last month the polar stratospheric vortex has weakened and is moving towards the “summer” mode as can be seen in the 10hPa and 50hPa charts below for 1200UTC on the 18th and forecast for the 28th April.

: 2: Upper Troposphere

CFSv2 200hPa contours (top row) and CFSv2 anomaly (middle) and NMME (lower row) for May to August 2021 hint at a less mobile patterns across the Atlantic for May and June but more cyclonic patterns near the UK for July but more especially August.

B: Lower Troposphere:

Selection of May model solutions using April 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

May data from WMO

Selection of forecast anomalies for May from WMO : Left to right WMO super ensemble, Brazil, UKMO, Canada, Germany, Japan, France, China, Russia. (see http://www.weather-info.co.uk/wxsvc/seaslatest.html for full sequence)

Selection of Summer (June to August) solutions using April 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly. The full set of graphics can be seen at http://www.weather-info.co.uk/wxsvc/seaslatest.html

Data from WMO

WMO super ensemble of 10 international models.

German Met Service (DWD)

C: Comparing the output of seasonal models for 2021 January, February and March based on December 2020 data for the UK and Ireland.

For graphics and details see Verification review 2020 Dec 2021 January February

Review of details looked for in seasonal forecast.
Temperature. For the three months together: England Wales and N Ireland were on aggregate above normal and Scotland below. Jan was cold and other months milder.

Rainfall. For the three months together: Above normal but the detail more varied especially the large areas of below average in March.

Sunshine Scotland totals above average but elsewhere below average although the month to month picture is more complex.

Pressure. South below and North above average. Higher pressure generally in March.

Results: Monthly detail poor in almost all models. DWD and to some extent ECMWF got the warming trend but all models failed to get below normal January followed by warmer Feb and Mar. Toulouse, NMME and CFSv2 got some idea of the trend in precipitation.

Scoring for the three month season will attempt to state good, fair, poor or no signal.

1. Russia: Temp poor . PPN poor .
2. USA – CFS2 : Temp good . PPN fair .
3. UKMO Contingency: Temp good . PPN good .
4. UKMO : Temp fair . PPN good . PMSL fair
5. USA – IRI : Temp no signal . PPN no signal .
6. KMA APCC : Temp good . PPN fair .
7. JMA : Temp fair . PPN poor . PMSL poor
8. NMME : Temp good . PPN fair .
9. WMO : Temp good . PPN fair .
10. BCC : Temp good. PPN good .
11. NASA – Temp fair . PPN fair .
12. Brazil: Temp fair. PPN poor. PMSL good.
13. CanSips : Temp fair. PPN good .
14. IMME : Temp good . PPN fair .
15. Copernicus Temp fair . PPN good . PMSL poor
16. CMCC Temp fair . PPN fair . PMSL poor
17: DWD Temp poor . PPN poor. PMSL poor
18. EC Temp fair PPN fair PMSL poor
18b JMA Temp poor. PPN poor. PMSL poor
19 UKMO Temp good . PPN good . PMSL
20. MF Temp fair . PPN fair . PMSL poor
21 NCEP Temp good . PPN fair . PMSL poor
22 JAMSTEC: only available for main seasons.
23 ECMWF (monthly) Temp: fair . PPN fair .

2: Forecast.

Remainder of Spring (2021 May)

The overall indication for May is for slightly above average temperatures.

Rainfall most models suggest below average rainfall in May which would be remarkable given the drier April although the end of April may well become wet.

May climate: 1981-2010 average mean temperature 11 or 12°C. Average May rainfall roughly 70mm but 150mm over moors and 40mm in drier east each month.

Summer 2021 (June July August)

Temperature near or slightly above average for the season with June possibly seeing the warmest anomalies and August the lowest.

Autumn 2021 (September October November).

Milder than average also wetter especially early in the period. Hints that October could be a drier month.

Winter 2021 /22 (December January February) very limited data.

Milder overall and also wetter than average which implies below average snowfall.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

By Master0Garfield – Created using WikiProject Tropical cyclones/Tracks. The background image is from NASA [1]. The tracking data is from the National Hurricane Center’s Atlantic hurricane database, Public Domain, https://commons.wikimedia.org/w/index.php?curid=90697173

Review and Experimental Long Range Forecast for SW England. March 2021.

Published 18 March 2021.

1. Influences.

Changes in sea temperature

Atlantic sea temperatures are generally warmer than climatology as are waters of the North Sea. Norwegian Sea, Baltic Sea and the Med. The tropical North Atlantic is forecast to remain slightly warmer than average through Summer 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific, just south of the equator, show a weakening La Nina with further noticeable warming having occurred in the East. Forecasts suggest that Pacific Sea Surface temperatures may remain in a La Nina or Neutral state through the remainder of 2021.

The North Atlantic Oscillation index (500hPa index shown below) has been slightly positive recently and is forecast to remain slightly positive for a short time before becoming uncertain.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

Up to the 17th temperatures averaged out around 7 Celsius which is slightly below the March average. There has been about 40% of normal rainfall and 60% of sunshine. High pressure was over the UK to start the month before becoming unsettled and at times windy in the second week of March, followed again by a spell of High pressure..

CPC graphic 7th to 13th March showing temperature anomalies and total rainfall in this period.

Looking back at the last three months Winter temperatures were a little colder than average across SW England and there was above average rainfall.

River flows and ground water levels in February 2021 were well above normal across SW England. Details can be found in the February 2021 Hydrological summary PDF

UK based data is available in The Hydrological Outlook which provides an insight into future hydrological conditions across the UK. Detail can be found at http://www.hydoutuk.net/

Global Flood Awareness (updated) System. February forecast for the period February to May indicates slightly above normal flood risk for SW England.

Glofas March forecast for March to June 2021. Blue above normal flood risk which probably mostly reflects the current above average ground water levels.

Atmosphere: Predictions.

A: 1: Stratosphere

Major warming in the stratosphere (see N Pole temperatures below) in January 2021 caused a reversal of the westerly flow across North America and a significant re-location of the polar stratospheric vortex towards Norther Russia. The SSW was deemed to have ended on 13th February.

The polar stratospheric vortex has strengthened into normal winter mode. Below the ECMWF 10hPa and 30hPa for 17/1200UTC and 27th March show the strong vortex relocating poleward and remaining stronger than climatology.

A: 2: Upper Troposphere

CFSv2 200hPa contours (top row) and CFSv2 anomaly (middle) and NMME (lower row) for April to August 2021 hint at a less mobile patterns across the Atlantic for April and June but more cyclonic patterns near the UK for July and August.

B: Lower Troposphere:

Selection of April to June solutions using March 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

The full set of graphics can be seen at http://www.weather-info.co.uk/wxsvc/seaslatest.html

Selection of Summer (June to August) solutions using March 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

CFSv2 SUMMER 2021 note there looks to be a cold bias in temperature across the N Sea in summer.

C: Comparing the output of seasonal models for 2020 December, 2021 January and February based on November 2020 data for the UK and Ireland.

For graphics and details see Verification review 2020 Dec 2021 January February

Review of details looked for in seasonal forecast.

Temperature. The North, mainly Scotland, was colder than average elsewhere mostly near average. The colder January mostly off set by above average December and February.

Rainfall. NW Highlands ended with below average rain but elsewhere values were mostly above average for the season.

Sunshine Northern areas had above average sunshine but southern areas had cloudier skies.

Pressure. Below normal for the season but above normal in N Scotland in Jan and Feb.

Temperature forecast was a little warm but got the idea of a milder February but not the cold January. Moscow output (WMO) which is often on the cold side got the idea of a colder January with near normal other months and some other models had January with smaller anomalies hinting at less mild. The colder than average season in Scotland was not indicated although the idea of above average snow in the north was correct. Above average rainfall was correct but the month to month detail was poor.

Models affected by the cold January and the lack of ability to forecast cold conditions.

Scoring for the three month season will attempt to state good, fair, poor or no signal. (E.O.E.)

1. Russia: Temp poor . PPN poor .
2. USA – CFS2 : Temp poor. PPN fair .
3. UKMO Contingency: Temp fair. PPN fair .
4. UKMO : Temp poor . PPN fair . PMSL fair
5. USA – IRI : Temp no signal . PPN no signal .
6. KMA APCC : Temp poor . PPN no signal .
7. JMA : Temp fair . PPN fair . PMSL poor
8. NMME : Temp poor . PPN poor .
9. WMO : Temp poor . PPN fair .
10. BCC : Temp poor. PPN poor .
11. NASA – Temp poor . PPN fair .
12. Brazil: Temp poor . PPN poor .
13. CanSips : Temp poor . PPN poor .
14. IMME : Temp poor . PPN poor.
15. Copernicus Temp good . PPN poor . PMSL poor
16. CMCC Temp fair . PPN poor . PMSL poor
17: DWD Temp poor. PPN poor. PMSL poor
18. EC Temp good . PPN poor. PMSL poor
19 UKMO Temp poor. PPN poor. PMSL poor
20. MF Temp poor . PPN poor . PMSL poor
21 NCEP Temp poor. PPN fair. PMSL fair
22 JAMSTEC: Temp poor. PPN good .
23 ECMWF (monthly) Temp: poor. PPN poor.

2: Forecast.

Remainder of Spring (2021 April May)

The overall indication for the April and May is for slightly above average temperatures with the strongest indication for above average values is in April.

Rainfall uncertain, probably near average overall but with some hints that April could be drier.

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Apr 8 or 9°C May 11 or 12°C. Average 1981 to 2010 rain similar totals in April and May roughly 70mm but 150mm over moors and 40mm in drier east each month.

Summer 2021 (June July August)

Temperature above average for the season with June possibly seeing the warmest anomalies and August the lowest, with values closer to the average.

Rainfall for the season uncertain but probably above average rain totals. Higher rain rates are typical of a warming atmosphere but may not imply an increase in the number of days with rain. Suggestion of one month being drier than average but no agreement as to whether it could be June or August. Slightly reduced indication for a wetter August.

Autumn 2021 (September October November).

Milder than average overall but perhaps near average, or even cooler than average, in November. Wetter than average Autumn with little agreement which month if any might be drier.

Winter 2021 /22 (December January February) very limited data.

Milder overall and also wetter than average especially early in the winter but February drier and possibly colder than average.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

Review and Experimental Long Range Forecast for SW England. February 2021.

Published 19 February 2021.

1. Influences.

Changes in sea temperature

Atlantic sea temperatures are mostly warmer than climatology apart from slightly cooler than average values around the UK. Norwegian Sea and Baltic Sea temperatures also remain above climatology despite the recent cold spell. The tropical North Atlantic is forecast to remain slightly warmer than average through Summer 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific, just south of the equator, show a well established La Nina although some noticeable warming has occurred in the East. Forecasts continue to suggest that Pacific Sea Surface temperatures may remain in a La Nina state through to 2021 although may be near neutral for the Spring.

The North Atlantic Oscillation index (500hPa index shown below) turned turned slightly negative early in December 2020 and has recently turned slightly positive and is forecast to remain slightly positive through the remainder of February.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

The recent cold and largely dry spell between the 5th and 14th has resulted in temperature averages being slightly below normal although this made be offset by milder SW which look like continuing until nearer the end of February when High pressure and a change in wind direction is likely. Rainfall to the 19th has been near or slightly above average and sunshine somewhat below average.

CPC graphic 7th to 13th February showing temperature anomalies and total rainfall in this period.

Looking back at the last three months, despite the colder January, temperatures have been near or a little above average across SW England and rainfall above average despite the drier November.

River flows and ground water levels in January 2021 were well above normal across SW England. Details can be found in the January 2021 Hydrological summary PDF

The forecast changes in the next month and three months can be viewed at Hydro UK http://www.hydoutuk.net/latest-outlook/

The reservoir levels in the SW of England were above the normal level as of February 7tht 2021.

Global Flood Awareness (updated) System. February forecast for the period February to May indicates slightly above normal flood risk for SW England.

Glofas February forecast for Feb to May 2021. Blue above normal flood risk.

UK based data is available in The Hydrological Outlook which provides an insight into future hydrological conditions across the UK. Detail can be found at http://www.hydoutuk.net/

Further graphics from the February outlook are available http://www.hydoutuk.net/archive/2021/february-2021/further-information-february-2021/

Atmosphere: Predictions.

A: 1: Stratosphere

JMA North pole observed temperature changes at 10hPa and 30hPa

Since then the polar stratospheric vortex has re-formed and strengthened into a normal winter mode. Below the ECMWF 10hPa and 50hPa show only limited stratospheric warming although a further weakening of the flow is evident across western Europe at 50hPa in the forecast for 28th Feb.

A: 2: Upper Troposphere

CFsv2 200hPa contours (top row) and anomaly (lower row) for March to May 2021 hint at a less mobile patterns across the Atlantic for April and May.

B: Lower Troposphere:

A selection of March to May solutions using February 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

A selection of WMO sourced March to May solutions using February 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

A selection of June to August solutions using February 2021 data can be seen at http://www.weather-info.co.uk/wxsvc/seaslatest.html

C: Comparing the output of seasonal models for 2020 November December and 2021 January based on October 2020 data for the UK and Ireland.

For graphics and details see Verification review 2020 Oct Nov Dec

Review of details looked for in seasonal forecast.
Temperature. Three month season slightly above normal except Norther Ireland slightly below. Nov and DEC above normal but January as much below normal as November was above. Look for colder January following milder Nov and Dec in most areas.

Rainfall. Scotland marginally below elsewhere above normal for the season. Look for November drier and then wetter.

Pressure. Overall below normal (WSW) but above normal in November, well below in December and slightly below in January except in NW Scotland were slightly above.

Comment: DWD and Tokyo had the correct temperature sequence milder start colder end. Washington, UKMO, DWD and Canada had the rainfall trend OK but were not “wet” enough with near normal suggested rather than above normal.

TABLE below is for 3 month data only. Scoring will state good, fair, poor or no signal for the three month season.
1. Russia: Temp no signal. PPN fair.
2. USA – CFS2 : Temp good . PPN good .
3. UKMO Contingency: Temp good . PPN poor .
4. UKMO : Temp fair. PPN fair . PMSL poor
5. USA – IRI : Temp no signal . PPN poor .
6. KMA APCC : Temp good . PPN no signal .
7. JMA : Temp good . PPN poor . PMSL poor
8. NMME : Temp good . PPN poor .
9. WMO : Temp good . PPN poor .
10. BCC : Temp good . PPN poor .
11. NASA – Temp fair . PPN poor .
12. Brazil: Temp good . PPN poor .
13. CanSips : Temp good . PPN fair .
14. IMME : Temp good. PPN fair .
15. Copernicus Temp fair . PPN poor. PMSL poor
16. CMCC Temp fair . PPN poor. . PMSL poor
17: DWD Temp fair . PPN poor. . PMSL poor
18. EC Temp fair . PPN poor. . PMSL poor
19 UKMO Temp fair . PPN poor. PMSL poor
20. MF Temp poor . PPN poor . PMSL poor
21 NCEP Temp fair. PPN poor . PMSL poor
22 JMA: Temp fair. PPN poor . PMSL poor
23 ECMWF (monthly) Temp: poor. PPN poor .

2: Forecast.

Spring (2021 March April May)

The overall indication for the Spring Season is for above average temperatures. March could well see some colder spells and could turn out to be near average. The strongest indication for above average values is in April although May is also likely to be warmer than average.

Rainfall uncertain, probably near average for the season but with some longer dry periods quite likely. There is a risk that March could be wetter than average with even a little snow over the moors but this could be followed by a drier April and near normal May.

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset.

Summer 2021 (June July August)

Temperature above average for the season with June possibly seeing the warmest anomalies and August the lowest, with values closer to the average.

Rainfall for the season uncertain but probably above average rain totals. Higher rain rates are typical of a warming atmosphere but may not imply an increase in the number of days with rain. June possibly drier than average but with a risk of above normal rainfall in July and/or August.

Autumn 2021 (September October November) limited data.

Milder than average but with near average rainfall.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

Review and Experimental Long Range Forecast for SW England. January 2021.

Published 19 January 2021.

1. Influences.

Changes in sea temperature

Atlantic sea temperatures are mostly warmer than climatology apart from slightly cooler than average values to the SW of the UK and Ireland. North Sea, Norwegian Sea and Baltic Sea temperatures also remain above climatology. The tropical North Atlantic is forecast to remain slightly warmer than average through to at least Summer 2021 (See Met Office graphic below).

Colder sea temperatures in the East Pacific, just south of the equator, show a well established La Nina and forecasts continue to suggest that the La Nina will remain active until at least Spring 2021 possibly trending towards neutral conditions for the summer months.

The North Atlantic Oscillation index (500hPa index shown below) turned turned slightly negative early in December 2020 and currently has about a 30% chance of turning positive at the start of February.

The negative NAO phase represents a weaker than usual difference in pressure North to South across the North Atlantic. Winds from the east and north-east are more frequent, bringing with them cold air, while the adjusted position of the jet stream leads to weaker and less frequent storms. As a result Europe is more likely to experience colder, less windy and drier winters during persistent El Nino conditions.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

The more blocked patterns during a negative phase can produce cyclonic or anticyclonic patterns over the UK depending on where such features become slow moving.

Recent Climatology – SW England

The first ten days of January were rather cold with frequent frosts but fairly dry. After the 10th it became less cold but with some rain. To the 19th of January temperature means across SW England are about 1 to 1.5C below the longer term average and rain totals to the 19th January are only about a third of average. Sunshine hours have been close to average. This can be seen in the snapshot for the period 3rd to 9th showing widespread below average temperature and rain/snow

Looking back at the last three months, temperatures have been near or a little above average across SW England and rainfall above average despite the drier November.

Looking back at 2020 for SW England the year was warmer, wetter but also sunnier in places. It very much looks like that when rain occurred it was “heavier”. For example in the Dawlish and Teignmouth area data suggests there were more dry days than average but also more days with 10mm or more of rain.

River flows and ground water levels in December 2020 were well above normal across SW England. Details can be found in the December 2020 Hydrological summary PDF

The forecast changes in the next month and three months can be viewed at Hydro UK http://www.hydoutuk.net/files/3916/1054/7577/2021_01_HO_Summary.pdf

The reservoir levels in the SW of England were above the normal level as of January 10th 2020.

Global Flood Awareness (updated) System. January forecast for the period January to April (shown left below) indicates slightly above normal flood risk for SW England. The image on the right shows a forecast for river flow based on the North Atlantic Oscillation (NAO) implying normal to above normal river flows across parts of the SW. For details see Outlook from NAO Analogues (hydoutuk.net)

Atmosphere: Predictions.

A: 1: Stratosphere

Major warming in the stratosphere (see N Pole temperatures below) has caused a reversal of the westerly flow across North America and a significant re-location of the polar stratospheric vortex towards Norther Russia. Although further warming is expected to continue forecasts suggest the vortex may return towards the N Pole and redevelop for a time before perhaps splitting the vortex in two weeks time.

ECMWF 50hPa and 10hPa analysis 17th and forecast for 27th Jan

NW Europe NCEP forecast temperature anomaly forecast have been trending to colder values in February and possibly March over recent days and the stratospheric warming may well be part of the reason.

A: 2: Upper Troposphere

CFsv2 200hPa contours (top row) and anomaly (lower row) for Feb to May 2021 hint at a more cyclonic February across the UK the less mobile patterns for March to May.

B: Lower Troposphere:

A selection of February to May solutions using January 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

Many models seem to have a problem forecasting colder than average values so the increase in the number of models showing near normal values might imply colder values in February and perhaps early March.

A selection of WMO sourced March to May solutions using January 2021 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

A selection of June to August solutions using January 2021 data

C: Comparing the output of seasonal models for October November and December based on September 2020 data for the UK and Ireland.

For graphics and details see Verification review 2020 Oct Nov Dec

Review of details looked for in the seasonal forecast.
Temperature. above average for season with November strongest for above normal after normal October. Rainfall. above average for season with November below average except N Ireland and W Scotland. Oct and Dec wet in S and E especially. Pressure. below average for season, November above average but Oct and Dec below.

TABLE below is for 3 month data only. Scoring will state good, fair, poor or no signal for the three month season.

1. Russia: Temp good . PPN mainly no signal Scotland and N Ireland good .
2. USA – CFS2 : Temp fair . PPN fair . (CFS2 monthly E3 suggested drier Nov)
3. UKMO Contingency: Temp fair . PPN no signal .
4. UKMO : Temp good. PPN poor . PMSL poor
5. USA – IRI : Temp no signal . PPN good .
6. KMA APCC : Temp poor . PPN poor .
7. JMA : Temp good – a little cool . PPN poor . PMSL poor (mean direction good)
8. NMME : Temp good. PPN fair .
9. WMO : Temp fair . PPN poor .
10. BCC : Temp fair . PPN poor .
11. NASA – Temp good . PPN poor .
12. Brazil: Temp good . PPN good . PMSL good
13. CanSips : Temp fair . PPN fair .
14. IMME : Temp good. PPN poor .
15. Copernicus Temp fair. PPN poor . PMSL poor
16. CMCC Temp fair. PPN poor . PMSL poor
17: DWD Temp fair. PPN poor . PMSL poor
18. EC Temp fair. PPN poor . PMSL poor
19 UKMO Temp fair. PPN poor . PMSL poor
20. MF Temp fair. PPN poor . PMSL poor
21 NCEP Temp good. PPN fair . PMSL fair
22 JAMSTEC: no data
23 ECMWF (monthly) Temp: fair . PPN good

Remainder of Winter (February 2021).

February may well start near normal or even slightly milder than average but there is a moderate risk of a change to be colder than average values – overall the month ending up near or slightly below average.. Rainfall is likely be near or above normal to start the month but trending drier, overall near normal totals for the month are possible. Increased risk of snow IF the change to colder types occurs.

Winter Climate: 1981-2010 February average temperature values for lowland areas 6 or7°C in the West and 5 or 6°C in the East. Rainfall; February. lowland areas 80-100mm but 60-80mm in east. Around 200mm over moors. Snow climatology for December to February less than 5 days lying snow in lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow. February possibly around 2 days on average with lying snow for low ground.

Spring (2021 March April May)

After a colder than average start Spring temperatures are likely to trend above average for May. April could see values close to normal. Overall above average values are likely for the three month season.

Rainfall uncertain but probably near or a little below average for the season. There is however a risk that March could be wetter than average followed by a drier April and near normal May.

Possibly some snowfall on the moors in March.

Early indication for Summer 2021 (June July August) limited data (data from eight global systems)

Temperature slightly above average for the season although Cornwall could be near average. Rainfall for the season uncertain but majority suggest close to average values although some models have wetter/drier than average.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Contains public sector information licensed under the Open Government Licence v3.0.

Review and Experimental Long Range Forecast for SW England. December 2020.

Published 18 December 2020.

1. Influences.

Changes in sea temperature

Apart from a semi permanent cooler area, centred near 55 North 30 West, Atlantic sea temperatures are mostly warmer than climatology as as are sea temperatures around the UK, Norwegian Sea and Baltic.

The tropical north Atlantic is forecast to remain slightly warmer than average through to at least Spring 2021 (See Met Office graphic below).

Wikipedia states that: ” The 2020 Atlantic hurricane season was the most active and the seventh costliest Atlantic hurricane season on record. In addition, it was the fifth consecutive above average Atlantic hurricane season from 2016 onward. The season featured a total of 31 (sub)tropical cyclones, all but one of which became a named storm. Of the 30 named storms, 13 developed into hurricanes, and six further intensified into major hurricanes, with one, Hurricane Iota, attaining Category 5 strength on the Saffir–Simpson scale.^{[nb 1]} It was the second season to use the Greek letter storm naming system, the first being 2005. Of the 30 named storms, 12 made landfall in the contiguous United States, breaking the record of nine set in 1916. The season was also the fifth consecutive season in which at least one Category 5 hurricane formed. During the season, 27 tropical storms established a new record for the earliest formation by storm number. This season also featured a record 10 tropical cyclones that underwent rapid intensification, tying it with 1995.^[2] This unprecedented activity was fueled by a La Niña that developed in the summer months of 2020.”

Colder sea temperatures in the East Pacific, just south of the equator, show the La Nina is well established and forecasts suggest that the La Nina will remain active until at least Spring 2021.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned positive in late October but turned slightly negative early in December.

The positive NAO phase represents a stronger than usual difference in pressure between the two regions. Winds from the west dominate, bringing with them warm air, while the position of the jet stream enables stronger and more frequent storms to travel across the Atlantic. These support mild, stormy and wet winter conditions in northern Europe

The negative NAO phase represents the reverse with a weaker than usual difference in pressure. Winds from the east and north-east are more frequent, bringing with them cold air, while the adjusted position of the jet stream leads to weaker and less frequent storms. As a result Europe is more likely to experience colder, less windy and drier winters.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

The more blocked patterns during a negative phase can produce cyclonic or anticyclonic patterns over the UK depending on were such features become slow moving. There is a chance that higher pressure will become established across the SW of England over the Xmas period and possibly last into the New Year but this is rather uncertain.

Recent Climatology – SW England

December to the 17th has been very slightly milder than the 1981 to 2010 average and has been slightly wetter in the east but much wetter in Cornwall and West Devon. Sunshine has been slightly below average so far in December.

Autumn temperatures have been near or a little warmer than average and rainfall was slightly below average for the season.

River flows and ground water levels in November 2020 were near normal across SW England. Details can be found in the Novembver 2020 Hydrological summary PDF

The reservoir levels in the SW of England were about normal of December 13th 2020.

Global Flood Awareness (updated) System. December forecast for the period December to March (shown below) indicates slightly above normal flood risk for SW England with typical river flood values as seen every two to five years (see lower section of graphic).

Atmosphere: Predictions.

A: 1: Stratosphere

Data from December 15th shows polar vortex established at 50 and 30hPa but with some warming occurring leading to a more complex stratospheric pattern and probably a relocation of the polar vortex to just north of Norway in a week or two. This may start to impact the weather patterns nearer the surface in January. It is possible that this could be the start of a significant stratospheric warming which could result in a colder January/February though this is too early to tell.

The temperature trace below indicates that temperature in the stratospheric polar region is cold enough for Polar Stratospheric Cloud formation which is implicated in Ozone depletion. This may be something to watch out for in the North polar region next Spring. http://www.weather-info.co.uk/ozone.html

A: 2: Upper Troposphere

CFsv2 200hPa contours (top row) and anomaly (lower row) for Jan Feb and March 2021 hint at a more cyclonic January and possibly February across the UK area possibly suggesting low centres could be steered further north than normal in the the remaining Winter months.

B: Lower Troposphere:

A selection of January to March solutions using December 2020 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

CFS2 E3 data JFM tends to be overly warm

WMO data. Three month average then separate months. Low resolution data.

SPRING (March April May) 2021

C: Comparing the output of seasonal models for September October November based on August 2020 data for the UK and Ireland.

For graphics and details see Verification review 2020 Sep Oct Nov

Review of details looked for in seasonal forecast.
Temperature. Looking for the West to be near normal and the East above normal also for a milder November in monthly detail.

Rainfall. Mixed three month pattern with above normal in NW and SE but areas below normal SW England Wales N Midlands NE England and far N Scotland. Looking for October signal to be wetter and other months drier.

Good temperature forecast but perhaps not the stronger anomalies in November. Rainfall fair in that overall values above normal but failed to get any detail. Pressure reasonable signal.

1. Russia: Temp fair – a little cool but reasonable sequence. PPN fair .
2. USA – CFS2 : Temp fair . PPN poor .
3. UKMO Contingency: Temp fair but overly warm . PPN fair .
4. UKMO : Temp good . PPN poor . PMSL good
5. USA – IRI : Temp no signal. PPN no signal .
6. KMA APCC : Temp fair . PPN no signal.
7. JMA : Temp good sequence but a little cool. PPN fair . PMSL good
8. NMME : Temp fair too warm. PPN good .
9. WMO : Temp fair. PPN poor .
10. BCC : Temp fair. PPN poor .
11. NASA – Temp good – got the milder November. PPN poor – almost reverse of actual .
12. Brazil: Temp Poor way to cold. PPN fair .
13. CanSips : Temp poor . PPN very good .
14. IMME : Temp fair . PPN fair.
15. Copernicus Temp fair. PPN fair. PMSL good
16. CMCC Temp fair . PPN poor . PMSL fair
17: DWD Temp good. PPN fair . PMSL fair
18. EC Temp fair. PPN poor . PMSL poor
19 UKMO Temp good . PPN fair. PMSL good
20. MF Temp poor . PPN poor . PMSL fair
21 NCEP Temp fair . PPN good . PMSL good
22. JAMSTEC: Temp good . PPN fair .
23 ECMWF (monthly) Temp: fair. PPN poor . PMSL

2. Forecast. SW England.

Remainder of Winter ( January and February 2021).

January temperatures are likely to be near normal; and there is a chance of below normal values for a period but by February milder than average values are more likely.

Rainfall indications are rather mixed but there is a reasonably strong indication for above average rainfall in January which could also mean above average snowfall, chiefly over the hills and moors. In February near normal rainfall is likely but perhaps above normal in western areas and below to the east of the moors with below average snowfall.

Spring (2021 March April May)

Milder than average temperatures seem likely for the season although March and April could see values close to normal and May could be significantly milder than average.

Rainfall uncertain but probably near or a little below average for the season. There is however a risk that March and / or May could be wetter than average.

Possibly a little snowfall on the moors in March.

Early indication for Summer 2021 (June July August) limited data (data from six global systems)

Temperature slightly above average for the season. Rainfall for the season near average but drier than average in June and July followed by a wetter than average August.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. November 2020.

Published 18 November 2020.

1. Influences.

Changes in sea temperature

Apart from a cooler area, centred near 55 North 40 West, Atlantic sea temperatures are mostly warmer than climatology as is the area around the UK, Norwegian Sea and Baltic.

The tropical north Atlantic is forecast to remain slightly warmer than average through to at least Spring 2021 (See Met Office graphic below).

Wikipedia states that “The 2020 Atlantic hurricane season is the most active season in terms of tropical depressions and named storms and has equalled or broken a number of records. It has been the second season after 2005 to use the Greek-Alphabet, the latest in season forming Category 5 hurricane on record (Iota). Record-breaking most storms to have formed before August through November. Most active September on record with 10 named storms. Record breaking most landfalls in the United States and Louisiana with 12 and 5, respectively. Record-tying 2 named storms in May, and 5 named storms in July. Record-breaking 6th straight season with at least one pre-season storm.

Colder sea temperatures in the East Pacific just south of the equator show the La Nina is well established and forecast suggest the La Nina will remain active until at least Spring 2021.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned positive in late October but there is about a 30% chance of the index turning negative by December 1st.

Why could a change in the NAO phase be important?

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

November to the 18th has been fairly mild with an average temperature around 11 Celsius, which is around two degrees or so above 1981-2010 mean for the month and rainfall has been near or a little above average so far.

Temperatures since summer have been near average with rainfall, taking September and October together, probably a little below average although this follows a “wet summer”.

Copernicus.eu climate data for month of October 2020 and year from November 2019 to October 2020

River flows in October 2020 were above normal across SW England and groundwater levels were also near or a little above normal in the eastern parts of SW England. Details can be found in the October 2020 Hydrological summary PDF

The reservoir levels in the SW of England were above average as of November 8th 2020.

Global Flood Awareness System. November forecast for the period November to February (shown below) indicates above normal flood risk for much of the UK and Ireland but near average risk in the south. In the river flow image there is just a hint of above average flows in the Exe estuary.

Atmosphere: Predictions.

A: 1: Stratosphere

Data from November 16th shows polar vortex established at 50 and 30hPa. The temperature trace below indicates that temperature in the stratospheric polar region is close to the cold values required for Polar Stratospheric Cloud formation which is implicated in Ozone depletion. This year has seen increased Ozone depletion in the Antarctic Polar Stratosphere and this may be something to watch out for in the North polar region next Spring. http://www.weather-info.co.uk/ozone.html

A: 2: Upper Troposphere

CFsv2 200hPa contours (top row) and anomaly (lower row) for Dec Jan and Feb hint at a more cyclonic February across the UK area and may suggest low centres could be steered further north than normal in the early part of winter.

B: Lower Troposphere:

A selection of December to February (Winter) solutions using November 2020 data are shown below, top row temperature anomaly and lower row precipitation anomaly.

CFS2 10 day mean (E3) data DJF. Tends to be overly warm.

WMO data. Three month average than separate months

SPRING (March April May) 2021

C: Comparing the output of seasonal models for August September October, based on July 2020 data.

For graphics and details see Verification review 2020 Aug Sep Oct

Temperature for the three month mean was correctly indicated as above average but few models got the month to month trend correct – EC and the WMO super ensemble perhaps did best. Rainfall forecasts were poor despite above average being indicated there was little indication for a drier September after a wetter August.

TABLE below is for 3 month data only:
Scoring will attempt to state good, fair, poor or no signal based upon
temperature being normal (fair) or above average (good). Rainfall above average and pressure below average. Errors and omissions excepted.
1. Russia: Temp mostly no signal. PPN no signal.
2. USA – CFS2 : Temp fair . PPN poor .
3. UKMO Contingency: Temp good . PPN good .
4. UKMO : Temp good . PPN no signal. PMSL no signal.
5. USA – IRI : Temp no signal. PPN no signal. .
6. KMA APCC : Temp good . PPN no signal..
7. JMA : Temp good . PPN poor. PMSL poor
8. NMME : Temp good . PPN poor .
9. WMO : Temp fair. PPN poor .
10. BCC : Temp good. PPN poor .
11. NASA – Temp good . PPN fair .
12. Brazil: Temp fair . PPN poor .
13. CanSips : Temp fair . PPN poor .
14. SAWS: : no data
15. Copernicus Temp no signal . PPN no signal . PMSL no signal
16. CMCC Temp no signal . PPN poor . PMSL poor
17: DWD Temp no signal. PPN no signal . PMSL no signal
18. EC Temp fair. PPN poor . PMSL poor
19 UKMO Temp good. PPN no signal. PMSL no signal
20. MF Temp no signal . PPN no signal . PMSL no signal
21 NCEP Temp no signal. PPN no signal. PMSL no signal
22. JAMSTEC: no data
23 ECMWF (monthly) Temp: fair. PPN poor
24 IMME Temp: fair . PPN poor

2. Forecast. SW England.

Winter (2020 December 2021 January February).

For the Winter season the mean temperatures is likely to be above average. That said there are some indications that the first half of the Winter could see near average values with some colder than average periods – the latter perhaps most likely in December. There is some agreement between models that February could be significantly milder than average.

Rainfall indications for the Winter season are rather mixed with a similar number of models showing below or above average values. There is a signal that December could be drier than average, January roughly 30% chance of wetter and 40% chance of near normal and February has a 60% chance of being wetter and possibly much wetter than average. The total number of days with measurable rain could end of below average though this is very uncertain.

Below average snowfall seems likely – snow most likely confined to higher moors.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

Spring (2021 March April May) limited data.

Milder than average temperatures seem likely for the season although March and April could see values closer to normal and May could be significantly milder than average.

Rainfall near or a little below average for the season although March could be wetter than average. The driest month varies between April in May is some of the models.

Possible a little snowfall on the moors in March.

Early indication for Summer 2021 (June July August) very limited data from China, Japan and Canada

Temperature and rainfall for the season near average but perhaps drier than average in August.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. October 2020.

Published 19 October 2020.

1. Influences.

Changes in sea temperature

Atlantic equatorial sea temperatures remain warmer than climatology as is the area area around the UK, Norwegian Sea and Baltic.

Colder sea temperatures in the East Pacific just south of the equator show the La Nina has strengthened.

The tropical north Atlantic is forecast to remain slightly warmer than average through to at least March 2021 (See Met Office graphic below).

Wikipedia states that “The 2020 Atlantic hurricane season is an ongoing tropical cyclone season which has featured tropical cyclone formation at a record-breaking rate. So far, there have been a total of 27 tropical or subtropical cyclones, 26 named storms, 9 hurricanes, and 3 major hurricanes.^{[nb 1]} With 26 named storms, it is the second most active Atlantic hurricane season on record, behind only the 2005 Atlantic hurricane season. It is also only the second tropical cyclone season to feature the Greek letter storm naming system, with the other season also being 2005.

The most recent storm (October 5th to 12th) Hurricane Delta was the record-tying fourth named storm of 2020 to strike Louisiana, as well as the record-breaking tenth named storm to strike the United States. “

A new storm shown “Epsilon” is likely to track near to Bermuda on the 23rd/24th of October 2020.

In the Pacific, sea temperatures continue to trend towards cooler / La Nina conditions which may now last until early Summer Spring 2021 before returning to neutral conditions.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned negative in near the end of September but is forecast to below positive before the end of October.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology – SW England

October to the 18th: Temperatures have been averaging around 11 Celsius or between 0.5 and 1 Celsius BELOW the 30 year average. Rainfall shows between 50 and 80% of the average, thanks mostly to the four wet days at the start of the month and mainly the 2nd and 3rd. Sunshine has so far been and near or slightly below average.

This follows drier than average September and a wetter summer with generally near normal temperatures.

River flows in September 2020 were near or slightly below normal across the SW and groundwater levels were also near normal in the eastern parts of SW England. Details can be found in the September 2020 Hydrological summary PDF

The reservoir levels in the SW of England (16th August) were above average as of the 11th of October.

Global Flood Awareness System. October forecast for Oct to Jan has above normal flood risk for much of the UK and Ireland. (Orange below normal Blue above).

Details of soon to be implemented improvements to the system can be found the the following URL https://www.ecmwf.int/en/about/media-centre/news/2020/new-upgrades-deliver-step-change-improvements-flood-forecasting

Atmosphere: Predictions.

A: 1: Stratosphere

Stratosphere polar vortex is forecast to strengthen towards winter mode as shown by the ECMWF 30hPa height and temperatures for October 18th 1200UTC and forecast chart for 28th October 2020.

A: 2: Upper Troposphere

October 6th data for CFSv2 200hPa contours for November 2020 to January 2021 shown in top row along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast is for above normal heights but with an increase in jet flow during January.

B: Lower Troposphere:

A selection of November solutions using October 2020 data are shown below.

Top row temperature anomaly and lower row precipitation anomaly.

WMO ensemble data for November 2020 : WMO BoM CMC and DWD

WMO ensemble data: Beijing Moscow Exeter and Toulouse

A selection of December to February (winter) solutions using October 2020 data are shown below.

Individual months, top row temperature anomaly and lower row precipitation anomaly.

C: Comparing the output of seasonal models for July August September 2020, based on June 2020 data.

For graphics and details see Verification review 2020 Jul Aug Sep

Temperature forecast for the three months had the correct idea even the suggestion of the colder and warmer areas.

Rainfall: The idea that the south could see one wetter month was correct and there were hints to wetter than average in places but overall not an especially helpful forecast

Models monthly:
Temperature: ECMWF BOM CMC TOKYO and Washington(WMO) had some idea of the cold July and warmer August.
Rainfall: NMME UKMO and CMC had hints at parts of the correct sequence

Scoring for three month season (from text if available) will attempt to state good, fair, poor or no signal.

Despite some models scoring good few had the monthly sequence anything light right.

1. Russia: Temp good. PPN no signal.
2. USA – CFS2 : Temp fair. PPN fair .
3. UKMO Contingency: Temp good. PPN good .
4. UKMO : Temp good. PPN mostly no signal . PMSL poor
5. USA – IRI : Temp no signal. PPN .
6. KMA APCC : Temp good. PPN no signal.
7. JMA : Temp good. PPN good. PMSL good.
8. NMME : Temp good. PPN poor.
9. WMO : Temp good. PPN poor .
10. BCC : Temp good. PPN fair .
11. NASA: Temp good. PPN poor .
12. Brazil:
13. CanSips : Temp fair. PPN fair .
14. IMME: Temp good. PPN fair .
15. Copernicus Temp good. PPN poor . PMSL fair
16. EC Temp good. PPN poor . PMSL poor
17. MF Temp good. PPN poor . PMSL poor
18. JAMSTEC:
19: ECMWF (monthly) Temp: fair. PPN poor
20: CMCC Temp good. PPN poor . PMSL good
21: DWD Temp poor. PPN poor . PMSL fair

2. Forecast. SW England.

Remainder of Autumn 2020 (November)

Temperatures are likely to be near or slightly above the 30 year average (1981-2010)

Rainfall more likely to be slightly below normal than above across SW England (confidence low)

November climate: 1981 to 2010 average mean temperature 8 or 9C°C. Average 1981 to 2010 rain 60 to 100mm East of the moors, 100-200mm west of the moors but over 250mm over the moors.

Winter (2020 December 2021 January February).

A milder than average Winter in indicated as well as each month being near normal or milder than average in most of the data. There is, however, a chance that December could be very close to average and a smaller risk that February could be a little colder than average.

Mixed rainfall indications with some of the wetter model solutions being cancelled out buy the drier ones in the WMO super ensemble. Overall though it seems more likely that total Winter rainfall may end up above average. There is a signal for the first half of Winter to be drier than average but the latter part could be much wetter than average and this may lift the overall winter total to be above average although the number of rain days could be below average. Below average snowfall seems likely – snow most likely confined to higher moors.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

Spring (2021 March April May) limited data.

Milder than average temperatures seem likely for the season although March and April could see values closer to normal and May could be significantly milder than average.

Rainfall near or a little below average for the season although March could be wetter than average.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at here.

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2 info

‘Copernicus Products’ as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via Free University Berlin

Climate data from The Met Office UK and NCEP USA