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

Published 19 June 2021.

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1. Influences.

Changes in sea temperature

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

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

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

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

Recent Climatology –  SW England

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

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

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

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

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

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

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

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

Atmosphere: Predictions.

A:  1: Stratosphere

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

2: Upper Troposphere

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

B: Lower Troposphere:

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

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

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

NASA GMGO
ECMWF

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

WMO super ensemble means.

Beijing China

BoM Australia
CPTEC Brazil
DWD Germany
ECMWF low res
Montreal Canada
Moscow Russia
Tokyo Japan
Toulouse France
UKMO UK Exeter
Washington USA – caution using newer averaging period in model hence may appear colder.

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

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

For graphics and details see Verification review March April May

Details looked for in seasonal forecast:

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

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

Sunshine above average due very sunny April

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

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


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


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

2: Forecast.

Remainder of Summer 2021  (July August)  

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

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

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

Autumn 2021  (September October November).

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

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

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.

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