Update 2 Nov 2016 see Forecast for November
(First Published 17 October 2016.)
CFS and UKMO model data from the end of October suggested that a drier than normal November with near normal or below normal temperatures is probable.
1. Potential influences.
Changes in sea temperature since mid September.
Sea temperature around the UK remain above normal but the colder area in the North Atlantic has expanded a little more. The La Nina in the Pacific remains fairly week and is expected to weaken further during the course of the winter months as shown by the consensus probability forecast below.
Whilst the La Nina is occurring it may be useful to look at the statistical relationship between the La Nina and precipitation in the UK area as shown in the graphic below. This suggest that the N and NW may be wetter than normal with other areas near normal or drier but given that the La Nina is fairly weak then the linkage may be unreliable.
Numerical (model) output.
A summary of the output for UK and Eire from several international seasonal models can be seen in the UK and Eire summary at www.weatherservice.co.uk. None of the available models suggest a colder than normal winter.
NMME output for November 2016 to February 2017 continues to show above normal temperatures although only slightly across the south in January, which is similar to last months forecast but with the lowest anomaly moved to January rather than December in the previous data. Precipitation signal has reduced across the SW compared to last months data but may just about end up above normal at least in northern and western parts of SW England for the winter season.
Indication for enhanced Atlantic westerly Jet flow has reduced compared to last month although still evident in some of the CFS2 output (later in the winter) but not at all clear in the NMME data. Both sets of anomaly suggest above normal heights across the S of UK.
Remainder of Autumn 2016 (November):
High pressure and easterly winds have recently brought temperatures nearer to normal from above normal in September and rainfall has so far been below normal for the first half of Autumn at least to the east of the moors. Although further periods of easterly winds are possible with drier than normal weather types over the UK in the second half of October this may not be true for parts of the SW of UK. For November there is broad agreement that temperatures will again be above normal and a return to wetter than normal weather is more likely than not. UPDATE 2 Nov 2017: CFS and UKMO model data from the end of October suggested that a drier than normal November with near normal or below normal temperatures is probable.
Climate: 1981 to 2010 November average mean temperature 8 or 9°C but nearer 6°C in upland areas. Maximum temperatures average 11 or 12°C but lower in upland areas. Average 1981 to 2010 rain 80 to 100mm to lee of Exmoor and Dartmoor (as low as 60mm over parts of Somerset) but in western areas 100 to 200mm is fairly typical with over 250mm over the tops of the moors.
Winter (2016 December, 2017 January and February) :
The winter is most likely to be milder than the long term average ( which does not rule out some frost), although parts of January and February may see temperatures only slightly above normal. This is a slightly less mild forecast than last month. (If this becomes a trend to colder type sin model data issued after the 17th then an updated may be added to this forecast.)
Near normal or above normal precipitation across the SW is most likely for the season. The N and W of the region in particular is more likely to have above normal rainfall and the SE and E parts of Devon, E Somerset and Dorset might be a little drier than normal.Below normal snowfall is more likely than above normal, which means just a little snow accumulation over the moors but not much elsewhere.
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.
Spring (2017 March April and May) :
Above average temperatures are most likely with near or below normal precipitation early in Spring made up to some extent by a wetter than normal May.
(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.)
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 or Click here for the Teignmouth and Dawlish summary
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/
NMME information: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1