Good afternoon. Today, the models have taken a further step forward towards a noteworthy cold spell during the second week of December. This includes a stunning 00z run from the ECMWF on which a large segment of the polar vortex drops into central Europe from around the 7th of December onwards. This produces bitterly cold conditions with a widespread snow risk across much of the UK. The 12z model output have continued this theme today, with both the JMA and the GEM going for a bitterly cold spell. The last time such cold weather was modeled for early December was 10 years ago, during 2012. The last time modeled cold weather verified was during December 2010, during which up to a metre of level snow fell across high ground in the north east of England.
That is not to say that level of cold or snow will be attained again, however there is scope for a noteworthy spell. In the last 24-36 hours or so, the models have taken a further step towards a more significant bite of wintry weather. This is characterized by a drop of a small polar vortex segment into central and western Europe. This could result in a relatively short-lived yet fairly severe bite of wintry weather which lasts a few days. The GFS was initially less keen on delivering this spell, producing a deeper low pressure over France and southern UK, shifting the pattern north. If this occurs, the cold air itself may also be shifted north of the UK as we approach the milder side of the jet stream (the southern side is always milder). However, this could also increase the risk of snowfall for central and northern areas as cold air clashes with moisture from the Atlantic.
In the solution offered from the other output, a short-lived severe cold spell would result in a few days of intense wintry conditions. Winds would be strong, as high pressure over Greenland squeezes against low pressure in-situ over the Mediterranean. This would fuel some potentially heavy periods of snow across the UK, with blizzard conditions possible, especially over high ground. This chart from the GEM (Canadian) weather model shows a strong north easterly wind over the UK on the 8th of December.
The sea surface temperatures are currently also significantly milder than average, which would fuel convection rates adding to the intensity of snow in any showers.
Before this potential, the outlook is fairly non-descript for the remainder of this week. Low pressure will remain out of the equation, leaving relatively dry conditions for most of us. Any rainfall will be refined to the higher ground of Scotland. It will be gloomy most of the time, with sunshine limited. Overnight frosts are possible in a few places, but mostly these will be kept at bay by cloudy skies. Fog may also be present at times, especially over high ground. By the weekend things will start to change as the risk of showers increases, and so does the breeze. Persistent rain is possible over parts of the east midlands & eastern scotland, where at times a few flakes of sleet & snow may be possible above around 350-400 metres above sea level. This risk is highlighted nicely by the following chart, where the hatched areas show precipitation falling as snow for this Sunday.
This theme will continue into Monday and Tuesday of next week before the “potential” bite of more severe wintry weather looms for the second week of December.
Overall, there is significant scope for a noteworthy bite of winter during the second week of December. This risk has somewhat increased in the last 24 hours to around 60%. We will continue to monitor this risk as time goes by. Admin.
