BBC monthly outlook
Summary
Unsettled weather for the rest of December
Saturday 8 December—Sunday 16 December
Rather unsettled overall with a short break.
Indications are that the rest of December and even early January will be characterised by wet, windy and generally mild conditions with a strong jet stream moving in from the Atlantic at times. The jet stream is a ribbon of strong winds in the upper atmosphere and helps to drive in weather systems to the UK.
Monday and Tuesday will see high pressure over most of the UK. As the high shifts to the northeast over Scandinavia on Tuesday, frontal systems will move a bit closer to the UK from the west and may bring cloud and patchy rain at times, although many places will stay dry. Beyond Wednesday, as the area of high pressure shifts eastwards towards Russia, we will see a return to unsettled conditions for the UK with plenty of outbreaks of rain and some windy days.
As we near the end of the week, there are hints of a strong storm coming in from the west but the exact timing and intensity of this event is still uncertain.
Monday 17 December—Sunday 23 December
Wet, mild and windy at times.
The wet, windy and mild theme continues for the week leading up to Christmas.
There is a good indication from various weather models that we will continue to see successive low pressure systems and their associated fronts sweep across the UK from the west, bringing some very windy days along with outbreaks of rain, sometimes heavy in the west and north. These weather systems will also bring milder Atlantic air and keep the colder, Polar air well to the north and east. We are likely to see occasional areas of high pressure moving through, bringing a brief respite from the wind and rain.
There is a risk that some of the low pressure systems could be strong and bring very strong winds and heavy rain to some areas. Confidence is low at this range on the exact timing and location of these potential storms due to the changeable nature of the jet stream.
Monday 24 December—Sunday 6 January
Staying mild with some very wet and windy weather
As we end December, there doesn't seem to be much change in the weather pattern, with low pressure systems moving across the UK bringing plenty of fronts, strong winds, and rain, along with milder temperatures. Western areas of the UK are expected to be the wettest and there are indications that rainfall could be well-above normal for the time of year for some areas, with a risk of flooding.
Strong winds appear most likely towards the end of the month. The generally unsettled theme dominated by low pressure systems will mean that any lowland snow around Christmas is unlikely. However, a brief cold snap between fronts cannot be ruled out, so there is perhaps just the faintest glimmer that some may see a white Christmas. As we head into the new year, the Jet stream looks set to dip south, bringing the low pressure track across the UK and into the Continent. This will bring colder air into the north with Scotland likely to see some snow even down to low lying areas. Further south it will stay wet, windy, and milder than Scotland but generally a bit cooler than December.
Occasional and brief cold snaps in the south are possible after the cold fronts move through, which could bring the risk for wintry showers to low-lying areas at times.
Next Update
Although a white Christmas looks unlikely, could we some snow somewhere in the UK?
https://www.bbc.co.uk/weather/outlook