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Weather news and views from Brian Gaze.
Posted Wed 5th December 11:42
A colder period next week looks probable. The catalyst for it will be an area of high pressure building over Scandinavia which leads to an easterly flow over the UK and much of the European mainland. The longer term outlook is very uncertain.
The London GEFS 00z plot shows the expected change. On the top half of the graph 850hPa temperatures drop from an exceptionally mild 10C to approximately -5C by December 10th. Remember those values are at approximately 1500m above sea level, but down at the ground we can expect temperatures to dip from approximately 13C to around 5C. Showers could turn wintry in the east but I would expect a mix of rain, sleet and snow at low levels rather than a winter wonderland. There isn't a huge amount of cold air to the north and east of the UK so it won't be like the Beast From The East spells we had in February and March.
What happens in the longer term? The GEFS indicates a transition back to more changeable weather as Atlantic weather systems move in and smash the Scandinavian block. The timing of that type of transition is often difficult to forecast because high pressure blocks have a tendency to stubbornly hang around. However, computer models have improved a lot in recent decades and they are consistently showing milder air from the Atlantic returning by mid December.
This morning's GFS 06z run illustrates how the breakdown is likely to develop. Essentially the cold air gets pushed away further eastwards and an Atlantic flow returns. The GFS 06z chart below shows that happening by December 13th but quite a few model runs keep the cold in place for several days longer.
Therefore I'd not be surprised if it is cold, especially in the east, as we head into the following weekend. There is also the possibility of the breakdown leading to a period of sleet or snow as the Atlantic weather fronts bump into the cold air over the UK.
A period of colder weather next week look very likely. Due to the lack of deep cold pooling over the continent, conditions for snow will be marginal and at low levels showers probably deliver a wintry mix. Computer model generally show a breakdown towards the middle of the month as weather systems begin returning from the Atlantic.
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