Published 18 February 2016.
Comment added 13 March 2016.
A major stratospheric warming event started in early March leading to reversal of wind at 50hPa and possibly aiding the formation/duration of high pressure in March in the UK area. Only a few of the CFS2 model runs later in February produced a drier than normal March presumably because of the uncertainty of when and where a warming event would develop. Some extended range models may not include enough or any stratospheric levels.
The sudden stratospheric warming arrived late enough not to impact of the winter which had been a concern for February 2016 in forecasts issued at the end of 2015..
End of comment.
This attempt at a Regional Forecast for SW England is based on international long range experimental forecast data available to 18 February 2016. The forecast covers Spring 2016 (March to May) and Summer 2016 (June to August) and a first look at Autumn. The summary forecast aims to test if any usable regional forecast 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
First a review of large scale features that might impact on the Seasonal Forecast.
Comparison with January (see previous post) shows an expansion of below normal North Atlantic sea temperature which may well impact on late Spring or Summer temperatures should prevailing winds be from the West or Northwest. In addition there is some weakening of the very strong Pacific El Nino.
There is broad agreement that Pacific sea temperatures will have changed from El Nino to a Neutral state before Summer 2016 but will probably have some impact during Spring.
Rainfall Probabilities linked to EL Nino.
The rainfall probabilities for Spring during an El Nino are shown below and generally indicate normal to above normal rainfall. The location of the above normal rainfall in earlier months has not been quite as suggested by the probabilities although the overall trend has been quite good.
Changes in the Stratosphere.
A “stratalert” was issued by JMA Tokyo for minor warming running into Canada on the 3rd of February. The minor warming period was deemed to have ended on the 17th February. During this period the stratospheric polar vortex split allowing a brief change to Northwest stratospheric winds across the UK area but no reversal. The polar vortex reset and Westerlies re-established over the UK area. According the ECMWF a further area of minor warming is set to repeat this process over the comping weeks as shown in the graphic below.
200hPa forecast height anomalies from NMME and CFSv2.
Not especially good agreement but some signs of rather cyclonic pattern over or near the UK early in Spring with enhanced jet strengths and despite above normal heights some indication of a stronger than normal jet for August and perhaps July.
Experimental Long Range Forecast for SW England.
Spring (March April and May) 2016:
The outlook for Spring remains fairly consistent in that the weather in March and April is likely to be unsettled/changeable as low pressures move near or across the UK. Hence at times windy with rain or showers and shorter drier, brighter or clearer intervals. Perhaps a little snow over the moors but less than normal. For May the low pressure tracks may well be further north allowing higher pressure in the south of UK. This means some longer drier spells compared to wet ones. Rainfall for the season as a whole is likely to be above normal with March and perhaps April most likely wetter than normal. In May normal or below normal rain is possible. Temperature average for the season probably above normal, perhaps less so in the West. March and May most likely to have above normal temperatures with April probably nearer normal or even cooler than normal.
(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.)
Summer (June July August) 2016:
Probably a typical summer with rather mixed weather. Rainfall overall a little above normal but possibly a little below normal in June, nearer normal in July and perhaps above normal in August. This is a change from indications in the January data.
Temperature near or a little above normal. Cooler Atlantic sea temperatures may result in reduced maximum temperature especially in the west. Some of the model data hints at average temperatures being above normal but not the maximum and minimum values. The strongest indication for above normal temperatures has edged back to June from July.
(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)
A first look at Autumn (September October November) 2016 with very limited data:
Possibly a drier and warmer September than average then a return to near normal values.
(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
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. doi:
UK climate details see:
Stratospheric images prepared by Freie Universität Berlin using European Centre for Medium Range Weather Forecasting data supplied by Deutscher Wetterdienst