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

Published 18 December 2020.

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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.

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)

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.

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.

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.

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.

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

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. 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

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

Published 19 September 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. Higher than average sea temperatures in the Gulf of Mexico, apart from the cool area near the NW coast of Florida (due to storm Sally) may aid the development of current potential storm “Beta”

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 February 2021 (See Met Office graphic above).

Wikipedia states that “The 2020 Atlantic hurricane season is an ongoing tropical cyclone season that has featured tropical cyclone formations at an unprecedented rate. So far, it has featured a total of 24 tropical cyclones, 23 named storms, eight hurricanes, and two major hurricanes.^{[nb 1]} With 23 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 Greek letter named storms, with the other season again being 2005.

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

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned positive at the start of August and heralded the drier and warmer weather. The index turned negative in mid August a forerunner of more unsettled and cooler weather. The positive phase is forecast to come to an end by in the last week of September as Atlantic mobility returns.

Recent Climatology – SW England

September to the 19th: Temperatures have been averaging around 16 Celsius or between 1.5 and 2 Celsius above the 30 year average. There has been above average sunshine and rather low rain totals – typically less than 10mm recorded so far.

This follows an average to slightly warmer summer – June and August were warmer but July was slightly colder than average. It was also a very wet summer in terms of rain total, although July was drier in SW England.

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

The reservoir levels in the SW of England (16th August) were above average as of the 13th of September.

Global Flood Awareness System. August forecast has above normal flood risk for the UK except perhaps inn the south. (Orange below normal Blue above).

Atmosphere: Predictions.

A: 1: Stratosphere

Stratosphere is transitioning towards winter mode as shown but the ECMWF 50hPa height and temperatures for 18th 1200UTC and forecast chart for 28th September.

A: 2: Upper Troposphere

CFSv2 200hPa contours for October to December 2020 shown in top row along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast of above normal heights more especially in the over western Europe in November and indication of stronger contrast in the north Atlantic in December.

B: Lower Troposphere:

A selection of October to December solutions using September 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

Selection of WMO data including the WMO super ensemble. Full set from http://www.weather-info.co.uk/wxsvc/seaslatest.html

For the Winter period December 2020 to February 2021.

For Spring 2021, March 2021 to May 2021.

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

For graphics and details see Verification review 2020 Jun Jul August

Comment: 040920 The idea that June and August would have the higher warmer anomalies in the south was correct, but the rain forecast was poor except perhaps for August in the south.

Scoring attempts to state good, fair, poor or no signal for the three month as a whole.

Comment 040920: Monthly data did not imply the correct temperature sequence in any model – several models got the idea of less rain in the south in July.
Season: Temp: To be correct near normal but above across Midlands and E/SE England and parts of W Scotland. Rain: needed to show above average rain except N Scotland and SE England.
1. Russia: Temp poor. PPN fair.
2. USA – CFS2 : Temp fair. PPN poor .
3. UKMO Contingency: Temp good . PPN fair .
4. UKMO : Temp fair . PPN Good for N and SE elsewhere poor . PMSL poor
5. USA – IRI : Temp good . PPN fair .
6. KMA APCC : Temp good . PPN poor/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 good . PPN fair .
12. Brazil:
13. CanSips : Temp good . PPN poor .
14. SAWS: :
15. Copernicus Temp good . PPN poor . PMSL poor
16. ECMWF Temp good . PPN poor . PMSL poor
17. MF Temp good . PPN poor . PMSL poor
18. JAMSTEC: Temp good . PPN poor .
19:
20: CMCC Temp poor . PPN poor . PMSL poor
21: DWD Temp fair . PPN fair . PMSL poor

2. Forecast. SW England.

Remainder of Autumn 2020 (October November)

Temperature are likely to be near or slightly above the 30 year average (1981-2010) October could see values closer to the average than in November.

Rainfall forecast lately have been poor and continue to be split for this period between drier and wetter solutions roughly 40% wetter/drier and 20% near normal. The start of October seems likely to be unsettled and rainfall for the month may well be near normal (wetter in the N of UK). November also probably near or a little above normal rainfall.

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. Autumn 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. October and November have similar number of rain days and totals range from around 70mm east of the moors to over 200mm over the moors.

Winter (2020 December 2021 January February).

A milder than average Winter in indicated as well as each month being near or milder than average. Caution models tend to be poor at picking colder types.

Mixed rainfall indications but Winter probably having above average rainfall and below average snowfall. There is a stronger signal for December being wetter than average compared to other months but February could also be wetter than average which is at odds with the data a month ago and illustrates the uncertainty. 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. Rainfall possibly below average in March but above in other months, hence above average for the season.

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. August 2020.

Published 21 August 2020.

1. Influences.

Changes in sea temperature

ssta08

Atlantic equatorial sea temperatures look warmer than climatology as area area around the UK, in the N Sea, Norwegian Sea and Baltic. The North Atlantic west of Britain has seen a reduction the the cooler than average areas and the Artic Circle shows very strong positive anomalies. Higher than average sea temperatures in the Gulf of Mexico may aid the development of current potential storms 13L and 14L.

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

tna_anom_20200801

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

In the Atlantic, 2020 so far ( Wikipedia link for details. ) there have been 14 tropical depressions 11 tropical storms and 2 hurricanes resulting in 45 deaths and nearly six billion US dollars worth of damage. One tropical storm resulted in no electricity to homes parts of New Jersey, USA, for a week due to trees falling over power lines.

Time line above and tracks below

1280px-2020_Atlantic_hurricane_season_summary_map

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

nino08

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned positive at the start of August and heralded the drier and warmer weather. The index turned negative in mid August a forerunner of more unsettled and cooler weather. The trend is for this to revert back to positive later in the month but for how long?

nao08

Recent Climatology – SW England

August to the 20th: Temperatures have been running over two degree above the long term average across the SW thanks to the very hot spell in the first half of the month when temperatures reached into the mid thirties Celsius.

The month had been drier than average until heavy rain fell on the 14th and more especially the 19th. These two days accounted for a months average rainfall. The recent heavy rain with thunderstorms led to flash flooding in, for example, Exeter and Barnstaple. In addition unseasonably windy conditions brought high seas to coastal areas in recent days (19-21 August) in association with storm Ellen and its parent Atlantic depression.

The week 9 to 15th gives a reasonable indication of the extent of the hot weather. au9to1508

The earlier part of the summer (June and July) showed near average temperatures after a warmer June and cooler July, but mostly above average rain (except the SE of England) despite a drier July in the south.

climsum08

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

river08

The reservoir levels in the SW of England (16th August) were close to average.

res08

Global Flood Awareness System. August forecast has near normal flood risk for southern parts of UK (Orange below normal Blue above).

glo08

Atmosphere: Predictions.

A: 1: Stratosphere

Stratosphere remains in summer mode as shown by the 50hPa chart for 20th August.

ecmwf50a12

A: 2: Upper Troposphere

CFSv2 200hPa contours for September to November 2020 shown in top row along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast of above normal heights more especially in the western Atlantic and southern Europe implies more changeable weather for the UK especially the in the north.

z200SON0820

B: Lower Troposphere:

A selection of September to November solutions using August 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly. (WMO graphics not available at time of writing).

NMME

CFS2

NASA

ECMWF

For the Winter period December 2020 to February 2021.

NMME winter

CFSv2 winter

NASA winter

ECMWF winter

If the WMO graphics become available they will be added to the weather-info site.

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

For graphics and details see Verification review 2020 May Jun Jul

Temperature: Reasonable indication for above average values although signal for slightly below average July was missed except in NCEP and DWD models.
Rainfall: Rain forecast fairly poor. UKMO and DWD got some idea of the sequence at least in S of UK.

Scoring is for whole season and will attempt to state good, fair, poor or no signal (similar probs for above normal, normal and below normal).

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

2. Forecast. SW England.

Autumn 2020 (September October November)

Temperature are likely to be above the 30 year average (1981-2010) for the season and may be above average for each month although September might be nearer average.

Rainfall above average rainfall is likely for the season although October in some models is drier than average in places but perhaps not the SW of England.

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 (2020 December 2021 January February).

A milder than average Winter in indicated as well as each month being milder than average. Caution models tend to be poor at picking colder types.

Mixed rainfall indications but Winter probably having above average rainfall and below average snowfall. Some hints that December and/or February could be less wet.

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 with near normal 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

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

Published 19 July 2020.

1. Influences.

Changes in sea temperature

170720ssta

Equatorial sea temperatures look warmer than climatology as is part of the N Sea, Norwegian Sea and Baltic sea temperature. The North Atlantic west of Britain has become much cooler than average although the western side of the Atlantic is warmer than average. The colder than normal sea temperatures to the west of the UK produces below average temperatures in August in some models, assuming winds are from a westerly direction.

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

tna_anom_20200701

The tropical north Atlantic is forecast to remain very slightly warmer than average through the remainder of 2020 (See Met Office graphic above).

No more Atlantic tropical storms are forecast for the remainder of July but there have been six tropical storms in the Atlantic/Gulf of Mexico area this season but no hurricanes. Names are Arthur, Bertha, Cristobal, Dolly, Edouard and Fay. – Wikipedia link to details.

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

170720nino

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been negative since late June and is forecast to remain so over the next few weeks which suggests a colder and wetter period may develop/continue across the N and E of Europe.

170720nao

NAO background information see the Met Office NAO information.

Recent Climatology – SW England

July to 19th Temperatures have been running slightly below average across the SW with other parts of the UK seeing cooler values. Sunshine also looks a little below average but rainfall has been well below average. Further north in the UK rainfall has been above average in places.

NCEP EU area temperature anomaly and rain total 5 to 11 July

Previously April to June had been warmer than average and drier in most places although June 2020 was very wet across the SW.

AMJ0720

River flows in June 2020 were normal and reflected the wetter month. Groundwater levels were above normal. Details can be found in the June 2020 Hydrological summary PDF

river

The reservoir levels in the SW of England (12th July) showed 75% storage which is close to average. Burrator was down to 47% in May but recovered during the wet June.

res

Global Flood Awareness System. July forecast has near normal flood risk for southern parts of UK (Orange below normal Blue above).

glo

Atmosphere: Predictions.

A: 1: Stratosphere

After a long period (during winter and spring) with a strong polar vortex the Stratosphere settled into summer mode around the end of April and remains with an easterly circulation as shown by the 30hPa chart for 18th July.

ecmwf30a12

A: 2: Upper Troposphere

CFSv2 200hPa contours for August to October 2020 are shown (top row) along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast of above normal heights through the period although in September lower anomalies may occur near the UK.

z200ASO0720

B: Lower Troposphere:

A selection of August to October solutions using July 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

NMME

CFS2 E3 data

NASA

ECMWF

In the WMO data white areas are where the probabilities of below/normal/above are similar hence there is no overall signal. Precipitation forecasts over the UK end up with no signal because the wet models cancel out the dry forecasts showing there is no agreement between the models.

WMO super ensemble 11 models.

UKMO

CMA

BOM

JMA

The available selection, including plots for Autumn and Winter, can be seen at the weather-info site.

C: Comparing the output of seasonal models for April May June 2020, based on March 2020 data.

For graphics and details see Verification review 2020 Apr May Jun

Temperature: the main thrust for above normal temperatures was correct though if anything understated. Areas of normal or below normal were limited.
Rainfall: Below average rainfall was correct for the season. Monthly variation hard to find in the models but NMME and ECMWF did quite well.

2. Forecast. SW England.

Remainder of summer 2020 (August)

Temperatures in August probably near normal, perhaps cooler near northern and western coasts and a little warmer than average in southern and eastern parts of the region.

August is likely to be drier than average although there is a hint of nearer normal rainfall in N Cornwall and NW Devon. There is a typical summer risk that locally thundery outbreaks may upset totals in a few locations.

August climate: 1981 to 2010 average daily mean temperature 16 or 17°C in many areas, a little cooler over the N coastal areas of Devon and Cornwall to 16 or 17°C and a few degrees cooler over the moor. Locally over 17C in parts of Somerset. Average rain in August typically 60 to 80mm, but 40 to 60mm in places especially East of the moors and in Somerset. Locally over 100mm across the moors.

Autumn 2020 (September October November)

Overall near or a little above average temperature seems likely, especially later in the season. Rainfall very mixed indication, most models have some longer dry periods but suggest September could be wetter in many areas but near normal in the SW . Overall signal is for near normal rain although eastern parts of the region could be drier than average.

Winter (2020 December 2021 January February) limited data.

A milder than average winter in indicated although February could see temperatures nearer average. Very mixed rainfall indications but Winter could end up near average although the first half of winter might be wetter than the second half. Below average snowfall is again likely.

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.

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. June 2020.

Published 19 June 2020.

1. Influences.

Changes in sea temperature

ssta03

Equatorial sea temperatures look warmer than climatology as are the N Sea, Norwegian Sea and Baltic sea temperature. The North Atlantic west of Britain remains mostly near or cooler than average towards North America. Colder sea temperatures in the East Pacific just south of the equator show the La Nina has strengthened.

tna_anom_20200601

The tropical north Atlantic is forecast to remain very slightly warmer than average through the remainder of 2020 (See Met Office graphic above).

No more Atlantic tropical storms are forecast for the remainder of June but there have been three tropical storms in the Atlantic/Gulf of Mexico this season. Names are Arthur, Bertha and Cristobal – see Wikipedia link to details.

In the Pacific neutral El-Nino conditions are likely to continue to trend towards cooler / La Nina conditions until later in the Autumn 2020. The GFDL model reverts to neutral or El Nino conditions rather faster than most models with the consensus being La Nina or neutral conditions into winter.

nino06

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been roughly neutral since mid May and is expected to remain so over the next few weeks.

nao06

NAO background information see the Met Office NAO information.

Recent Climatology

June to 18th has seen temperatures near average after a very warm or even hot start to the month. Rainfall has been well above normal (typically 80 to 90mm locally double this over some hilly areas due to thundery outbreaks. Sunshine rangled from below average in in parts of Cornwall to near average further east (limited data).

Spring 2020 recorded above average temperatures (March was near normal) and well below normal rain although February was very wet and March had nearer normal rainfall.

2020MAMT2M

May temperatures were above average across much of the globe but there were some colder spots including a good part of Northern Europe.

EZuuhI2XQAENQNg

River flows in May 2020 reflected the drier Spring although groundwater levels were above normal. Details can be found in the April 2020 Hydrological summary PDF

river06

The reservoir levels in the SW of England (14th June) showed 77% storage. Three of the main reservoirs are at 75 to 82% capacity but Burrator was down to 47%. The very wet 18th and night of 18th/19th will no doubt lift these values.

Global Flood Awareness System. June forecast has near normal flood risk for southern parts of UK (Orange below normal Blue above).

glofas06

Atmosphere: Predictions.

A: 1: Stratosphere

After a long period with a strong polar vortex the Stratosphere settled into summer mode around the end of April and remains with an easterly circulation as shown by the 30hPa chart for 18th.

ecmwf30a12

A: 2: Upper Troposphere

CFSv2 200hPa contours for July to September 2020 are shown (top row) along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast of above normal heights through the period.

z200JAS0620

B: Lower Troposphere:

A selection of July to September solutions using June 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

WMO

UKMO

Meteo France

Russia

ECMWF

Other models

CFS2 USA

NMME USA

NASA

The full selection, including plots for Autumn and Winter, can be seen at the weather-info site.

C: Comparing the output of seasonal models for March April May 2020, based on February 2020 data.

Most models got the idea of above average UK temperatures but not the nearer average March. Dry signal could have been stronger but some ideas about the NW being the least dry was good.

For graphics and details see Verification review 2020 Mar Apr May

2. Forecast. SW England.

Remainder of summer 2020 (July August)

Slightly above average temperatures are expected for the summer season with higher anomalies possibly in the second half of the summer.

Very mixed rainfall patterns but an indication for a wetter than average July and a near normal August although the east could be drier than average. Summer rain can be showery or thundery in nature with wide variations in rain days and rain totals across a region. It is not clear of above average rain means more wet days or just some days with higher rain total which has been a feature of recent years.

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 in July typically 60 to 80mm, but 40 to 60mm in places especially East of the moors and in Somerset. Locally over 100mm across the moors. August slightly small areas with the lower rain totals due to July often being drier than August.

Autumn 2020 (September October November)

Overall above average temperature seems likely, especially later in the season. Rainfall very mixed indication, most models have some longer dry periods but do not agree which month might be the drier or wetter month. Overall signal is for near normal rain although eastern parts of the region could be drier than average.

Winter (2020 December 2021 January February) limited data.

A milder than average winter in indicated although February could see temperatures nearer average. Rainfall could end up near average but at least one moth is likely to be wetter than average and again some longer drier spells are suggested but little agreement as to when. Below average snowfall (snow chiefly over the moors) is most likely.

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.

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. May 2020.

Published 19 May 2020.

1. Influences.

Changes in sea temperature

170520ssta

Equatorial sea temperatures look warmer than climatology as are the N Sea and Baltic sea temperature. The North Atlantic west of Britain remains near or cooler than average towards North America but have warmed relative to average closer to the UK.

tna_anom_20200501

The tropical north Atlantic is forecast to remain very slightly warmer than average through Spring and Summer 2020 (See Met Office graphic above). The first Atlantic Tropical Storm “Arthur” developed off Florida but will weaken soon.

arthur

In the Pacific neutral El-Nino conditions are likely to trend towards cooler / La Nina conditions during Summer and into early Autumn 2020. The CFSv2 model looks quicker than most of the other ensemble systems of the NMME in completing this transition. The timing of the change from El Nino to La Nina might impact on the Atlantic hurricane season, El Nino tending to depress the formation of Atlantic Tropical Storms.

170520nino

Met Office Atlantic tropical storm forecast for June to November 2020 issued 19 May 2020: “The most likely number of named tropical storms (winds of at least 39 mph) predicted to occur in the North Atlantic during the June to November period is 13, with a 70% chance that the number will be in the range 9 to 17. The 1981-2010 long-term average is 12.

The most likely number of hurricanes (winds of at least 74 mph) predicted to occur in the North Atlantic during the June to November period is 7, with a 70% chance that the number will be in the range 5 to 9. The 1981-2010 long-term average is 6.

The most likely number of major hurricanes (winds of at least 111 mph) predicted to occur in the North Atlantic during the June to November period is 3, with a 70% chance that the number will be in the range 2 to 4. The 1981-2010 long-term average is 3.

Note: Tropical Storm Arthur occurred in May 2020 and is therefore outside the period covered by this prediction (June-November).”

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been mostly negative since then end of March and is forecast to be roughly neutral over the next few weeks.

180520nao

NAO background information see the Met Office NAO information.

Recent Climatology

May to 18th has seen temperatures near average on the whole but with well below normal rainfall (5 to 15mm) and above average sunshine.

Because of the very wet February running average for the three months is above average.

190520clim

River flows in April 2020 reflected the drier January and February conditions and groundwater has largely recovered to above normal values in all areas. Details can be found in the April 2020 Hydrological summary PDF

190520ground

The reservoir levels in the SW of England (10th May) showed 89% storage. Three of the main reservoirs are at over 90% capacity but Burrator is down to 68%.

res

Global Flood Awareness System. May forecast has a surprisingly high risk for southern parts of UK and may be because of high ground water following the very wet February. (Orange below normal Blue above)

190520glow

Atmosphere: Predictions.

A: 1: Stratosphere

After a long period with a strong polar vortex the Stratosphere settled into “summer” mode around the end of April.

strat

A: 2: Upper Troposphere

FSv2 200hPa contours for June to August 2020 are shown (top row) along with the anomalies from CFS (lower row). Forecast of above normal heights through the summer period.

z200JJA0520

B: Lower Troposphere:

A selection of June to August solutions using May 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

White areas are where the probabilities of below/normal/above are similar hence there is no overall signal for this period from the WMO data.

WMO

UKMO

JAPAN

MOSCOW

ECMWF

NASA

NMME

CFS2 E3 data

The full selection can be seen at the weather-info site.

C: Comparing the output of seasonal models for February, March and April 2020, based on January 2020 data.

There were some good indications for above average temperatures and the drier trend. NASA was one of the few monthly anomalies that picked out the near normal March and only UKMO and perhaps to lesser extent ECMWF picked the very much milder April.
CFS2 and NMME indicated drier for April as did Brazil and to a lesser extent Toulouse – some others did but were mostly drier throughout so rejected if did not get wet start to season.

For graphics and details see Verification review 2020 Feb Mar Apr from January

2. Forecast. SW England.

Summer 2020 (June July August) limited data

The main theme is for above normal temperatures although some indication that they may only be slightly above. August and possibly June could have the higher anomalies in the south. Rainfall very variable monthly detail from the models but probably below average for the season except perhaps in the North. Hints at August being above average in places, mainly in the south.

Slightly above average temperatures are expected for the summer season with higher anomalies possibly in the second half of the summer

Very mixed rainfall patterns but an indication for a drier than average June and July but possibly a wetter August. Summer rain can be showery or thundery in nature with wide variations in rain days and rain totals across a region.

Autumn 2020 (September October November) limited data.

Overall above average temperature, especially later in the season. Rainfall may be below average early in the season followed by a wetter October although indications from models are quite mixed.

Winter (2020 December 2021 January February) very limited data.

A milder than average winter in indicated although February could see temperatures nearer average. Rainfall could end up below average but January looks to be wetter and February drier. Below average snowfall (snow chiefly over the moors) is most likely.

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.

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. April 2020.

Published 17 April 2020.

1. Influences.

Changes in sea temperature

150420ssta

Equatorial sea temperatures look warmer than climatology as are the N Sea and Baltic sea temperature whereas the North Atlantic west of Britain remains near or cooler than average.

170420tna

The tropical north Atlantic is forecast to remain very slightly warmer than average through Spring and Summer 2020 (See Met Office graphic above).

170420nino

In the Pacific neutral or weak El-Nino conditions are likely to trend towards cooler / La Nina conditions during Summer and into early Autumn 2020. The CFSv2 model looks quicker than most of the other ensemble systems of the NMME in completing this transition. The timing of the change from El Nino to La Nina might impact on the Atlantic hurricane season, El Nino tending to depress the formation of Atlantic Tropical Storms

University College London forecast issued 7th April 2020 suggests that the Atlantic hurricane activity in 2020 may be 25% above the long-term norm: Intense Hurricanes=3 (70 year average 3) Hurricanes=8 (70 year av 6) Tropical Storms=16 (average 12). Met Office outlook available in May.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been mostly negative since then end of March but is forecast to be roughly neutral over the next few weeks.

170420NAO

NAO background information see the Met Office NAO information.

Recent Climatology

April to the 16th has been very mild with temperature anomalies between 2 and 3 Celsius although cold easterly winds held windward coastal sites lower. It has also been extremely dry with only 3 to 6mm (1 to 4%) of the normal month rain. Rainfall totals were more than doubled on the 17th by a band of rain that moved north from France bringing 5 to 15mm of rain.

170420jfmclim

River flows in March 2020 reflected the very wet conditions in February followed by nearer normal rain in March with high river flows in most areas except for Aberdeenshire. It is perhaps a surprise that groundwater in eastern England is still below average. Details can be found in the March 2020 Hydrological summary PDF

070420river

The reservoir levels in the SW of England (12th April) showed 95% storage. All main reservoirs are at over 90% capacity.

120420res

Global Flood Awareness System. April forecast (high) risk for early part of the forecast decreasing through to July 2020 and largely reflects the well above average rain in February and early March.

170420glofas

Atmosphere: Predictions.

A: 1: Stratosphere

A second phase of significant warming occurred at 10hPa and more recently down to 30hPa as the very persistent stratospheric polar vortex slowly warms out.

170420jmastrat

ECMWF 10 and 30hPa 16/1200UTC data shows that despite ongoing warming the polar stratospheric vortex is reluctant to be eroded completely but forecast for the 26th shows than warming out is almost complete and the transition to summer mode should take place by the end of April.

160420stratec

A: 2: Upper Troposphere

CFSv2 200hPa contours for May to August 2020 are shown (top row) along with the anomalies from CFS (lower row) and NMME (middle row). Suggestion of above normal heights through the period.

0420z200mjja

B: Lower Troposphere:

A selection of May to July solutions using April 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

White areas are where the probabilities of below/normal/above are similar hence there is no overall signal for this period from the WMO data.

WMO combined multi model ensemble

UKMO

Meteo France

Russian Met Centre

Canada

ECMWF

BoM Australia

Korea Met Agency

A selection of June to August solutions using April 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

NMME Summer 2020

CFS2 summer 2020

NASA summer 2020

ECMWF summer 2020

UKMO summer 2020

The full selection can be seen at the weather-info site.

C: Comparing the output of seasonal models for January, February and March 2020, based on December 2019 data.

Observed three month period was above average but did anyone get the trend to cooler/near normal in March?

Forecast temperature summary was good for the three month forecast with some idea of less mild in north later.

Observed rainfall for the three month period was above average but largely due to a very wet February, January and March were near or below average across the UK.

Rainfall was OK with the above average indication but not the drier east of UK in Jan and Mar. The seasonal total rain swamped by the very wet Feb.

For graphics and details see Verification review 2020 Jan Feb Mar from December 2019

2. Forecast. SW England.

End of Spring 2020 (May)

Most models suggest above average temperatures for May.

Precipitation is uncertain but most models suggest drier than average.

May climate: 1981-2010 average mean temperature 11 or 12°C. Average 1981 to 2010 rain typically 60 to 80mm. Locally as low as 40mm in parts of E Devon and over areas of Somerset but 100 to 150mm over the moors.

Summer 2020 (June July August) limited data

Slightly above average temperatures are expected for the summer season with July suggested as the month least likely to have above normal values (a change from last month which suggested June rather than July).

Very mixed rainfall patterns but an indication for a drier than average June but possibly wetter July. August solutions split between wetter and drier. Summer rain can be showery or thundery in nature with wide variations in rain days and rain totals across a region.

Autumn 2020 (September October November) limited data.

Overall near or above average temperature and above average rainfall is suggested for the season but no agreement for any particular month to be wetter or drier.

Winter (2020 December 2021 January February) very limited data.

A milder than average winter in indicated with near or above average rainfall and below average snowfall (snow chiefly over 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.

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. March 2020.

Published 20 March 2020.

1. Influences.

Changes in sea temperature.

160320ssta

Noticeable changes in the Atlantic include a much larger area of cooler than average North Atlantic sea temperatures to the west of the UK and Eire also a much warmer area near the equator between Africa and South America. The North Sea, Baltic and Med remain above normal.

tna_anom_20200301

The tropical north Atlantic is forecast to remain very slightly warmer than average through Spring and Summer 2020 (See Met Office graphic above).

180320nin34

In the Pacific neutral or weak El-Nino conditions are present but forecasts suggest conditions are likely to trend cooler during Summer and into early Autumn 2020 – see CFSv2 and NMME multi model ensemble forecast above.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been mostly positive since early December 2019 and is forecast to remain slightly positive over the next week before trending negative at the end of March which might hint at a colder start to Spring.

190320nao

NAO background information see the Met Office NAO information.

Recent Climatology

March, to the 19th, has been slightly cloudier, milder and wetter than average.

Winter, as can be seen in the graphics below, has been very mild and in most places wet due to a very wet February.

190320djf

190320winter

River flows in February 2020 reflected the very wet conditions with high river flows in most areas apart from Aberdeenshire. It is perhaps a surprise that groundwater in eastern England is still below average. Details can be found in the February 2020 Hydrological summary PDF

1903river

The reservoir levels in the SW of England (15th March) showed 97.5% storage. The less than 100% value is due to Colliford as the the other main reservoirs are at 100% capacity.

190320res

Global Flood Awareness System March forecast (high) risk through to June 2020 largely reflects the well above average rain in February and early March. The risk reduces from late April or early May.

Atmosphere: Predictions.

A: 1: Stratosphere

A second phase of significant warming is occurring at 10hPa and to some extent at 50hPa but from unusually low temperature values.

190320strat1

ECMWF 10 and 50hPa 18/1200UTC data shows that despite ongoing warming the polar stratospheric vortex is reluctant to be eroded completely.

190320strat2

A: 2: Upper Troposphere

CFSv2 200hPa contours for April to August 2020 are shown below (top row) along with the anomalies from CFS (middle row) and NMME (lower row). Suggestion of enhanced Atlantic jet for April towards or just north of the UK imply unsettled types but possibly higher pressure further south.

z200AMJja0320

B: Lower Troposphere:

A selection of April to June solutions using March 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly.

White areas are where the probabilities of below/normal/above are similar hence there is no overall signal for this period from the WMO data. Problems with the WMO web site in South Korea has made access to this data difficult.

APRIL TO JUNE 2020

UKMO

Brazil Met Service

German Met Service

Canadian Met Service

Australian Met Service

If they become available further examples from WMO will be added to the weather-info site.

ECMWF

NASA USA

CFS2 USA

NMME USA

SUMMER JUNE TO AUGUST 2020

ECMWF

NASA

CFS2

NMME

C: Comparing the output of seasonal models for December 2019, January and February 2020, based on November data.

Observed Temperature. Well above average for the season and each month.

Forecast temperature: Most models forecast the above normal temperatures but perhaps not the detail.

Observed Rainfall. Above average all areas thanks to an exceptionally wet February. January was the relatively less wet month.

Precipitation Forecast: Above average rainfall was forecast but the much wetter February was not well forecast with some models suggesting a less wet month.

Observed Pressure. Below average but near or slightly above in far South.

Pressure Forecast was correct.

For graphics and details see Verification review 2019 Dec 2020 Jan Feb from Nov data.

2. Forecast. SW England.

Spring 2020 (April May)

Some models suggesting near normal temperatures for April and perhaops early May and then above normal but models seem not to be able to reliably predict colder months. The near average signal may imply a colder than average April.

Precipitation is uncertain but probably a drier than average period in April and possibly early May before a return to near normal rainfall amounts.

Summer 2020 (June July August) limited data

Near or perhaps only slightly above average temperatures are expected for the summer season with June suggested as the month least likely to have above normal values. Very mixed rainfall patterns but an overall indication for a drier than average summer, although August could be wetter than average.

Autumn 2020 (September October November) limited data.

Overall above average temperature and rainfall is suggested for the season but September could be drier than average.

Winter 2020 (2020 December 2021 January February) very limited data.

Another milder than average winter in indicated with near average rainfall resulting in below average snowfall (snow chiefly over 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.

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 Free University Berlin

Climate data from The Met Office UK and NCEP USA