Experimental Long Range Forecast for SW England

Published 18 April 2016.

The end of Spring – May 2016:

A rather chilly start to May but temperatures most likely ending up near normal for the month as a whole. Probably some warm days for the south and east of the region where temperatures might be just a little above normal compared to Cornwall and the north and west of Devon where values may be a shade cooler than normal. Rainfall totals probably near normal but with a chance that Cornwall, along with North and West Devon and parts of West Somerset could be wetter than normal.

(1981-2010 average mean temperature roughly  May 11 or 12°C but a few degrees cooler over the moors and just a little higher in parts of Somerset and valleys in S and E  Devon. Average 1981 to 2010 monthly rain for May 60 to 80mm locally up to 150mm over the high moors but 40-60mm around Exeter and widely across Somerset levels and SE Doreset.)

Summer  (June July August) 2016:


Probably a typical summer, with rather mixed weather but with the strongest indication for longer dry spells being in July. No strong indication for an especially warm summer despite some signs of above average pressure.

Rainfall for the season near normal probably due to a wetter August and perhaps parts of June, offset by a drier July. Potential for the S and E of the region to see below normal rainfall overall.

Temperature near or a little above normal in parts of E Devon, Somerset and parts of Dorset but cooler than normal Atlantic sea temperatures may result in near or below normal temperatures elsewhere. This could be due to reduced day time maximum temperature making for rather cool feel to some days. July may be a slightly warmer month than June or August compared to the average, which is not unusual.

(1981 to 2010 average 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  (September October November) 2016:

Overall temperature for the season slightly above normal, perhaps a little below at first then becoming above normal. Rainfall below normal for the season but September may be wetter than normal.

La Nina may conditions may become established in the Pacific by Autumn which may start to influence global weather patterns. For the SW of England this implies drier than normal conditions may develop through the Autumn. The onset of this potential impact is very uncertain.

 (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)


Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary and brief verification of previous Long Range Forecast summaries can be seen at   http://www.weatherservice.co.uk

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 (Due to technical problem at the ISP no updates to weather-info.co.uk have been possible since April 8th and backup forecast pages are available through the weatherservice web link.)

Potential influences that could affect the forecast.



Sea Temperature over a very large areas of the North Atlantic remains below normal. A negative anomaly expected to persist through summer although with reduced area. Summer maximum temperatures may well be affected, especially in Eire and the western half of the UK.

In the Pacific the weakening El Nino condition is predicted to return to neutral conditions and may well change to La Nina conditions starting during the summer. The strength of the La Nina for the end of the year is uncertain.


Probability of El Nino/Neutral/La Nina occurring, by season.





Rainfall statistical probability April to June during El Nino

For the summer months the impact of El Nino is reducing hence the graphics have not been included. One impact of neutral Pacific sea temperature conditions is the likely increase in the number of Atlantic tropical storms and hurricanes compared to last year. This is because El Nino conditions work to inhibit Atlantic Tropical storm formation.

For the Autumn of 2016 should a strong La Nina develop then the rainfall probabilities may worth looking at again



Sept to Nov probability of Drier/Wetter/Normal rainfall during La Nina conditions.


Stratospheric warming continued into April with a major warming event declared at 30hPa in the Tokyo issued STRATALERT bulletin. The major warming ended notification waas issued on April 8th by which time the strong winter polar vortex had been completely warmed out. For comparison with graphics in earlier posts the ECMWF 30hPa analysis for the 17th April is shown below.



Text summary of the seasonal model output from the UK, USA, Canada, China, Russia, Japan, Korea, Brazil and South Africa can be seen in the UK and Eire summary at www.weatherservice.co.uk

North American Multi Model Ensemble and CFS2 graphics for the UK area are shown below. CFS2 has been consistent in suggesting a drier July and wetter August SW England and this signal can be seen in the NMME output. CFS2 is less keen on above normal temperatures, being nearer normal (month anomaly of +/-0.5C). March CFS2 output suggested parts of the UK might have below normal temperatures this summer but this signal has reduced in April model output with each month showing anomalies centred on near normal.


NMME April data. May to November predicted Temperature (top) and Rainfall (bottom) monthly anomalies. Red above model normal blue below model normal.


Above CFS2 by season and below CFS2 rainfall anomaly by month.



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/

Stratospheric images prepared by Freie Universität Berlin using European Centre for Medium Range Weather Forecasting data supplied by Deutscher Wetterdienst

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

CFS2  info