BBC monthly outlook
Summary
Turning rather chilly and unsettled
Wednesday 16 January—Sunday 20 January
Turning chilly. Wetter over the weekend
The rest of the week looks to be generally unsettled with periods of rain and some dry spells. It will turn quite cold with some wintry precipitation possible in higher terrain, and even down to low levels in Scotland at times.
Wednesday looks to be rather cloudy and wet, with a cold front crossing the UK bringing some heavier outbreaks of rain for most through the morning and early afternoon. As the front clears to the east, winds will shift to the north and bring in some sharp or even thundery showers, mainly to northern and western regions. These may be wintry in higher spots. Overnight showers will drift in to the east coast bringing a wintry mix to some. Turning noticeably colder than of late.
Thursday will be brisk but dry, with some chilly winter sunshine in the afternoon. Overnight will become quite cold with most places seeing frost. The end of the week and weekend will see a return to more unsettled weather, with a low pressure system slowly pushing in from the west, bringing clouds and rain to most. The best of any dry weather will be in the east. Wintry showers are likely in Scotland, with snow or sleet present even down to low levels in places. However, snow accumulation at low levels is unlikely.
Monday 21 January—Sunday 27 January
Colder at times with a risk of snow for some
A mixed week of weather appears most likely with wet and breezy conditions giving way to colder but drier weather at times. As the week progresses, there is an increasing likelihood of some sharp night frosts in between any bands of rain. There will also be an increasing risk of a brisk easterly wind developing from mid-week providing a brisk cold snap for much of the country, with a chance of snow showers in the northeast. However, there is still a large degree of uncertainty in this forecast, and cold air may fail to reach as far west as the UK.
High pressure in the Atlantic with a low pressure system in Western Europe are the culprits behind the colder weather. The exact location and strength of the low in Western Europe is the main source of uncertainty for this week, and will depend a great deal on a winter storm leaving the United States on Monday 21st. Overall, a chillier week is expected than recently. However, there is a chance (about a 30% probability) that it remains less cold with somewhat milder and wetter conditions predominating.
Monday 28 January—Sunday 10 February
Colder than average with rain and snow at times
There continues to be the likelihood of some cold and perhaps wintry weather through the end of January and early February. In our previous outlooks we have looked at conditions in the upper atmosphere over the North Pole. At the start of the year, there was a dramatic rise in the temperature within the upper atmosphere over Siberia. Meteorologists call this kind of event a Sudden Stratospheric Warming or SSW. They happen several times per decade and are part of the natural variability of the global climate system.
The recent SSW event combined with other global scale weather patterns are now favoured to bring colder weather to the UK through the end of January and into February. However, indications are that this cold weather is more likely to come in pulses, perhaps with occasionally milder and wetter interludes in-between (unlike the extreme and prolonged cold we experienced during the 'Beast from the East' episode in February/March 2018). Nevertheless, temperatures are likely to be below the seasonal average more often than not with some sharp night frosts and a mixture of bands of rain and snow moving across the UK. However, it will likely be a bit drier than the seasonal average as well, so widespread snowfall does not appear likely.
There are chances of more severe, sustained cold developing (about a 25% probability) - a lesser chance is for much milder and wetter conditions to prevail.
Next Update
We will continue to monitor the duration and severity of the expected colder period of weather, and attempt to pin down the changeability next week.
https://www.bbc.co.uk/weather/outlook