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

Published 19 July 2021.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

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.

WMO multi model ensemble mean anomalies
Biejing China

BoM Australia

Brazil
DWD Germany
ECMWF
Canada
Russia
S Korea
Japan
France
UK
USA

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.

NMME Winter 21/22
NASA winter 2021/22

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. 20146(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. May 2021.

Published 18 May 2021.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

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.
NMME 7th May 2021
NASA

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)
BoM Australia
Brazil Met Service
Canada Met Administration
BCC China
European Centre
Meteo France
Japan Met Agency
Korean Met Administration
Russia (Moscow data)
UK Met Office
USA Climate Prediction Center

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.

WMO super ensemble AUTUMN
NMME AUTUMN

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.

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. June often drier than July and July drier than August.

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.

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) very limited data.


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

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. 20146(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.