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

Published 18 May 2021.

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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.

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

Published 19 April 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 west of Ireland are cooler due to lack of SW to W winds. The colder Northerly types of late have resulted in cooler values in the southern North Sea despite most of the North Sea being warmer than average. The Norwegian Sea, Baltic Sea and the Med are also mostly near or above normal. The tropical North Atlantic is forecast to remain slightly warmer than average through Summer and Autumn 2021 (See Met Office graphic below).

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

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

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

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

Recent Climatology –  SW England

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

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

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

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

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

River Flow from Climate Forecast.

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

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

Atmosphere: Predictions.

A:  1: Stratosphere

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

North Pole temperature at 10hPa and 30hPa

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

: 2: Upper Troposphere

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

B: Lower Troposphere:

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

CFS2, NASA, ECMWF and NMME

May data from WMO

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

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

CFSv2
NMME
NASA
ECMWF

Data from WMO

WMO super ensemble of 10 international models.
Washington
UKMO
Meteo France
Korea Met Agency
Canada Met Agency

ECMWF

German Met Service (DWD)

Brazilian Met Service
Bureau of Met Australia
China Met Agency.

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

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

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

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

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

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

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


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

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

2: Forecast.

Remainder of Spring  (2021 May)

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

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

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

Summer 2021  (June July August)  

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

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.

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. Hints that October could be a drier 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) very limited data.


Milder overall and also wetter than 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.

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