Published 18 May 2016.
Summer (June July August) 2016:
Pressure is forecast to be higher than normal hence the summer may be better than an average summer for at least southern parts of the UK.
In the South West of England starting like a typical summer with rather mixed weather bringing rain or showers. Then a chance of a drier spell, perhaps starting in June, but more likely in July. This signal has been fairly consistent in some of the model output with the strongest indication for longer dry spells being in July. August though may see above normal rainfall, possibly due to thundery showers.
There is a chance that the S and E of the region may have below normal rainfall for the season as a whole. Elsewhere rainfall for the season may end up near normal, mostly due to a wetter August and parts of June, despite a drier July.
In parts of East Devon, Somerset and Dorset, the temperature for the summer is more likely to be near or a above normal than below normal. Cooler than normal Atlantic sea temperatures may result in near or below normal temperatures in the remainder of Devon and also for Cornwall, possibly due to reduced day time maximum temperature making for a 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. There are some hints that August could be more humid, with higher than normal minimum temperatures possibly related to thundery rain outbreaks. There is also a low probability of some hot days (more than 6 degrees C above normal) may occur, most likely the east of the region.
(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 for the season 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:
Average temperature for the season probably slightly above normal. November in particular is expected to be mild but with more frost than normal in October.
Rainfall below normal for the season with October and possibly September, drier than normal but with a wetter than normal November.
La Nina may conditions expected to 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 which is consistent with at least some of the model forecasts.
(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
Potential influences that could affect the forecast.
There has been quite a change in the Atlantic Sea temperatures over the last month with warming around the UK area. Despite that long range models retain a cooler than normal North Atlantic Sea Temperatures through the summer. If correct this would slightly depress afternoon temperatures in prevailing westerly type.
The El Nino in the Pacific has weakened considerably and the consensus forecast is for La Nina conditions to become established through the middle of 2016 onwards.
RAINFALL PROBABILITIES LINKED TO LA NINA.
For the summer months the impact of El Nino is reducing hence the rainfall 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. Because El Nino conditions work to inhibit Atlantic Tropical storm formation this year tropical storms probably occurring at the normal rate but potentially developing stronger hurricanes due to warmer than normal equatorial sea temperatures. UKMO suggest above normal number of hurricanes in 2016.
For the Autumn of 2016 a moderately strong La Nina is expected to develop hence the the rainfall probabilities based on IRI statistics may be worth looking considering and this is shown below
Text summary of the seasonal model output from the UK, various USA, Canada, China, Japan, Korea, Brazil and South Africa can be seen in the UK and Eire summary at www.weatherservice.co.uk
For the summer data from Japan and China have lower temperature forecast for the UK but the majority of the model output suggests normal or above normal temperatures. Brazil suggests lower than normal pressure and above normal rainfall but several other models imply higher pressure. UKMO has perhaps the strongest signal for above or well above normal temperatures but also the risk of well above normal rain in parts of UK, including the SW. For details follow the link to UK summary or look at the links in the seasonal section of weather-info.co.uk/fcst.html
200hPa height anomaly NMME (top) plotted with CFSv2 (bottom) suggests above normal heights but with enhanced upper flow in June and more ridging in July. August although above normal heights are shown more toughing is implied near or just W of UK.
Anomalies suggest most upper level ridging is in October and then enhanced westerly upper pattern for November.
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