Often on the cold side. Sleet and snow in places.
After a cold and bright start to December for many of us, the second half of this week will become wet and windy, as a large low pressure system arrives and then stalls over the UK. It will be cold enough for some snow, more likely over higher ground in the north and west but even southern regions could be at risk of some wet snow for a time. The middle two weeks in December will be very changeable but often on the cold side, with the prospect of some sleet and snow especially over the higher ground. Ridges of high pressure will be persistent over the north Atlantic steering areas of low pressure south-eastwards over the UK and down into southern Europe. This reduces the threat of gales over the UK, with France and Spain receiving the strongest winds instead. The weather over the Christmas week is still finely balanced. At the moment, an unsettled spell with near average temperatures is most likely. It's a bit too early to realistically look at the chance of a white Christmas yet!
Colder, windier and more unsettled. Hill snow.
On Wednesday a weak frontal system moves south east across the UK, bringing rain and then colder air. This front will be followed by a deepening low pressure system stalling over the UK between Thursday and Saturday. This will bring rather miserable weather on Thursday, grey and wet with rain for all areas as well as increasing winds, peaking in strength on Friday when there will be an uncomfortable wind chill.
There is the risk of hail showers for western regions, especially Northern Ireland, Wales and southwest England, while the best chance of any sunshine on Friday will be across Wales and southern and western counties of England. It will become cold enough Thursday to Saturday for some snow to get mixed in, especially over northern and western hills but possibly to lower levels in Scotland at times. Some sleet or wet snow cannot be ruled out further south but looks unlikely to be disruptive.
By Sunday morning the low pressure system should be moving away southwards, leaving drier, sunnier, calmer but cold conditions. Frost, ice and fog patches on Sunday night. A few wintry showers will still be possible, especially for Northern Ireland and across northern and western areas of Scotland, Wales and England.
Staying cold. Occasional rain. Upland sleet & snow
Monday will see a new area of low pressure moving in from the east, introducing extensive cloud cover to northern, central and eastern areas with showers or longer spells of rain, sleet and hill snow moving west. Most snow of any consequence will be over the Pennines, Peak District and eventually southern Scotland. There will be a lot of dry and bright weather across the south-west of the country thanks to a weak high pressure ridge here. It will stay rather cold with a frost early and late in the day in some western areas.
Tuesday has low confidence on the behaviour of a new low pressure system expected to approach from the west. It looks like this will bring rain and wet hill snow or sleet to Wales and England, even possibly in the south of England (more likely sleet than snow here). Scotland will more likely miss most of the precipitation thanks to a high pressure ridge building to the north, which should push the low pressure system south-eastwards. Just a few scattered showers are possible. There is a slight chance that the low will track farther north, bringing rain and hill snow to Scotland, and milder but rainy conditions to the south.
On Wednesday and Thursday models suggest a better chance of a high pressure ridge across Scotland and Northern Ireland which may be expanding southwards a little. This should deliver a lot of dry, chilly weather with the possibility of a few showers towards eastern coasts and perhaps over the far south of England, and those areas could be rather windy. There is, however, a slight chance that this high pressure ridge will develop farther south, which would mean wetter and milder westerly wind flows, especially across the northern half of the UK.
Further low pressure areas will then slide south-eastwards over the UK towards the end of the week, keeping the changeable and chilly pattern going.
Christmas week will be unsettled but less cold
Through the middle of December, a transient high pressure ridge will extend from Scandinavia across the UK to join an extensive north Atlantic high pressure. The resultant weather will depend on the exact position of this ridge. Most likely there will be several dry and settled days during the middle of the month for many of us, with overnight frost and crisp winter sunshine. Occasional low pressure areas will still break south-eastwards through this ridge to maintain the changeable theme. These systems will initially struggle to introduce much milder weather. In fact, they may help to extend the chilly weather through mid-December as they pull in colder winds from the north and north-east. The threat of winter gales is rather low through the week of 14th to 20th December.
Eventually it looks like deeper areas of low pressure will start to track across the UK again, while high pressure systems dominate over Scandinavia and out in the north Atlantic. This should mean a return to more consistently unsettled conditions with periods of rain and occasionally stronger winds. Snow is still a threat in Scotland for a time but the low pressure track should be far enough north for milder air to get drawn across southern UK with temperatures most likely rising nearer normal.
So, at the moment the forecast guidance suggests that the chilly weather in the first half of December may start to relinquish its hold on the UK somewhat just before Christmas! It's too early to more specific yet, but the next couple of updates should offer a bit more detail on the week before Christmas.
Upcoming updates will hone the late December forecast to see what likelihood there is for snow over Christmas.