BBC monthly outlook
Summary
Temperatures above average with unsettled weather
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Wednesday 25 December – Sunday 29 December
Dry around Christmas then mild into the weekend
A brief ridge of high pressure on Christmas Day will keep the country day and provide some clear blue, sunny skies in many areas. Cloud will likely only linger at times in western Scotland and Northwest England. However, it will also feel a bit cooler than recent days throughout. Light winds and mostly clear skies overnight will see widespread fog mainly in central and eastern Britain, which may turn dense in places. This will tend to clear before sunrise on Boxing Day, except for in parts of the Southeast. A weather system will be arriving in the morning on Boxing Day bringing bands of rain to the Southwest, spreading northeast across the UK. This will make for a much wetter and windier day that Christmas, with rain eventually reaching all parts of the country. A second weather system will push in from the southwest overnight and into Friday, bringing further rain.
However, the main feature these systems will bring to the UK is some warmer air from the tropical Atlantic. It is still December though, so don't unpack your shorts and t-shirts just yet! Temperatures will be well above average through the weekend with afternoon highs possibly reaching up to 13C in places. As far as rain, high pressure over the continent will tend to push weather fronts off into the Atlantic and keep things dry for many. Fronts will occasionally reach into northern areas, mainly Scotland and Northern Ireland, and bring some patches of light rain and cloudier skies. It will be breezier here and in Wales too, but winds will tend to be fairly light across much of England.
Monday 30 December – Sunday 5 January
Rather mild but turning widely wet and windy
The very end of December and start of the new year will continue to see very mild air over the UK as weather systems stay to the north or northwest. High pressure over the continent that is expected to keep things mostly dry for England and parts of Wales will decline and shift heading towards January, allowing for some rain to return more widely across the country.
This will be a gradual shift over a few days, with a cold front bringing some light rain into England at first before the weather pattern makes a more dramatic shift for the second half of the week. Low pressure is expected to become the dominant weather feature, with a potential for some stronger lows to move close to or over the UK. This will bring in some stronger winds and heavier rain more widely across the country, but notably into southern England which until this point will have escaped most of the rain.
Northern areas, particularly Scotland and Northern Ireland, will see more frequent heavy rain and stronger winds consistently through the week. Despite the return of a more unsettled weather pattern and more frequent rain across the country, things will remain quite mild for the time of year. This is because high pressure will continue to feed tropical air in from the southwest that will get picked up by the Atlantic weather fronts and brought into the UK. There any snow, even on hills, is unlikely into early January with the only exception being the very highest ground in the Highlands.
Monday 6 January – Sunday 19 January
Staying unsettled, possibly stormy at times
Wind patterns are expected to shift to more westerly as we head deeper into January, bringing more active fronts and more frequently unsettled weather. As cold, Arctic air reaches into the North Atlantic from Greenland and Iceland, some strong low pressure systems could develop and track over the UK. This will bring in a risk of some stormy weather, especially strong winds and heavy rain. The winds will tend to be strongest in northern areas nearer to the low pressure centre, while high pressure lingering to the southwest keeps things a bit calmer in the South.
Moving into the second full week of January, the confidence in the forecast begins to drop as model guidance diverges quite a bit.
We expect the low pressure tracks to begin to dip further south and reach into Europe as high pressure further declines. This will mean that things will turn less windy and wet over the UK, but also some cooler polar air will be able to infiltrate in from the north. This will mean temperatures will return to near average, especially in the north, and wintry showers will make a comeback. Rain will continue to impact much of the South, so continued high river levels and flooding is expected. Mild air may cling on here from occasional warm fronts, so overnight frosts or lowland snow for the southern half of the UK remains unlikely.
Further ahead
As 2019 goes out on a mild note, will 2020 continue to look like it will have a rather stormy start?
https://www.bbc.co.uk/weather/outlook