Updated 5th December
Covering the period 12th December - 3rd January
Despite a mild first week, mean temperatures are expected to be a little below normal for most parts of the country, typically by between 0.5 and 1.0C, though northern Scotland, Northern Ireland and south-west England may come out closer to normal.
Rainfall totals will be above normal in Northern Ireland and in south-west England, but generally below normal elsewhere, particularly in northern Scotland.
Sunshine totals will be well above normal in western Scotland and north-western England, but below normal in Northern Ireland. They will tend to be close to normal in south Wales and southern England, and rather above normal elsewhere.
Monday 12th December - Sunday 18th December
This week will begin very mild with south-westerly winds and frequent rain for the north-west, but with a return to colder, quieter conditions near the end of the week.
The 12th is expected to be cloudy for most of the UK, and wet across much of Scotland and Northern Ireland, but it will be mostly dry in England and Wales, with high pressure over Europe ridging into the south-east. A large low pressure complex will bring fronts north-eastwards on the 13th and 14th, though again these will probably miss much of England and Wales, and will mostly affect north-western Britain. Temperatures will be well above the seasonal norm, especially by night, with daytime highs of around 9-12C for most, and night-time minima not dropping far below 10C.
Low pressure will slacken somewhat to the north of Britain between the 15th and 18th, allowing high pressure to develop over Scandinavia. Westerly winds will remain dominant, bringing some rain belts at intervals, but there will also be drier, brighter interludes in between the rain belts, and temperatures will fall close to the seasonal average, generally reaching between 6 and 9C by day by the end of the week, and with one or two frosty nights particularly affecting the south. Rainfall amounts will continue to be small in south-eastern Britain.
Relative to the 1981-2010 reference period, temperatures will mostly be 2 to 3C above normal, by both day and night, though less than 2C above in parts of south-east England and north-west Scotland and Northern Ireland.
Rainfall totals will be above normal in Northern Ireland and close to normal over much of Scotland and north-west England, but will be below normal elsewhere.
Sunshine totals will be somewhat below normal in Northern Ireland, but generally close to normal elsewhere in the UK with a relatively sunny second half of the week offsetting the dull first half.
Monday 19th December - Sunday 25th December
High pressure will establish close to the British Isles during this week, bringing dry and fairly cold weather to much of the UK although milder, wetter weather will affect Northern Ireland, south Wales and southern and south-western England at times. Blocking anticyclones are expected to be particularly dominant over Scandinavia. There is potential for some snowfall late in the week with colder air coming in from the north-east, which may also interact with systems attempting to push in from the North Atlantic, but considerable uncertainty over its extent at this stage, with the emphasis likely to be on dry cold weather.
Mean temperatures are expected to be below the long-term average, probably by around 2C, although northern Scotland is expected to be closer to normal. Rainfall totals will be close to or above normal in south-western Britain and in Northern Ireland, but it will be drier than average elsewhere, particularly so in western Scotland. Sunshine totals are more open to uncertainty, as cloud can prove quite stubborn under anticyclonic conditions at this time of year. Broadly speaking, sunshine totals are likely to be below normal in the south-west and in eastern coastal counties, but above normal in western Scotland and Cumbria.
Rest of the month
Monday 26th December - Tuesday 3rd January
The weather is expected to remain mostly cold and dry early in the period but with a signal for relatively unsettled weather to push in from the south-west towards the New Year, with pressure falling in the North Atlantic. With pressure set to remain high over Scandinavia, there is potential for some frontal snow, but a lot of uncertainty over the extent of lowland snowfall, as it depends on how strongly any cold continental air establishes from the north-east. Temperatures will tend to recover close to the seasonal norm by the end of this period, but will be below normal early in the period. Overall, negative temperatures of 1 to 2C are expected, with rainfall totals much below normal in central and northern Scotland, but rising close to or above normal in the south and in Wales and Northern Ireland due to a wet end to the period. Other areas are likely to be drier than average but not exceptionally so.