Updated 23rd November
Covering the period 30th November - 22nd December
Mild, windy and wet start to December, then turning more settled
Mean temperatures will be about 1.5C above the long-term average across much of the country, but closer to 1C above in Northern Ireland. The first half of December will be warmest relative to normal in the south, but after that, southern areas will turn colder.
Rainfall totals will be above normal in Northern Ireland, western Scotland and north-west England, near-normal in other western areas, and below normal in the east.
Sunshine totals will be well above normal in eastern Scotland, and moderately above normal in eastern parts of England. Western parts of the country will have close to or slightly below normal sunshine (below-average sunshine most likely over north-west England and south-west Scotland) but with generally dull weather early in December largely offset by sunnier weather after mid month.
Monday 30th November - Sunday 6th December
Britain's weather will be dominated by a stronger-than-usual westerly flow during this period, with a strong Icelandic low and high pressure dominant over southern Europe. The 30th is expected to start off bright and showery in most parts of the country, with snow over high ground in Scotland, but mild, wet and windy weather will spread from the south-west during the day. It will become dry with some sunshine for central, southern and eastern England on the 1st December, but with cloudy wet weather persisting elsewhere. On the 2nd and 3rd a belt of heavy rain will move south-eastwards across the country, followed by brighter showery weather, when it will turn colder again with some wet snow possible at low levels in Scotland, and significant snowfalls over the Highlands. Between the 4th and 6th, mild, cloudy and windy weather is expected to prevail with south-westerly winds, although central and northern Scotland will be colder at times with some wintry showers to low levels at times and snow over the Highlands.
Mean temperatures will be very close to the long-term normal across northern Scotland, and only about a degree above over the rest of Scotland and Northern Ireland. However, it will be much milder than average over England and Wales, with temperatures 3 to 4C above the 1981-2010 average in south-east England. Rainfall totals will generally be above normal except in eastern England, where they will be near or slightly below average. Sunshine totals will show a marked west-east split, below average in the west (particularly Cumbria and south-west Scotland) but above normal in most eastern areas, particularly northeast Scotland.
Monday 7th December - Sunday 13th December
High pressure will ridge up from the south during this period resulting in longer periods of dry quiet weather, especially over southern parts of Britain. It will remain generally mild during the early to middle part of the week thanks to westerly winds blowing around the northern flank of the high pressure, but near the end of the period, the high pressure will pull colder continental air into southern and eastern parts of the British Isles. Atlantic weather systems moving to the north of the anticyclone will continue to bring belts of rain to the north, especially early in the period, but these rain belts are expected to become increasingly confined to the north and west of Scotland.
Temperatures will nonetheless be above normal everywhere, typically by 2 to 3C. Rainfall totals will remain above normal in the north and west of Scotland, but it will be drier than normal over England, Wales, Northern Ireland, and eastern Scotland, particularly so in southern England. Sunshine totals will be above normal in most eastern coastal districts but below average elsewhere, particularly around the Irish Sea.
Rest of the month
Monday 14th December - Tuesday 22nd December
This period is likely to begin with high pressure in charge, and fairly cold conditions are likely to develop over most of the country, but it is likely to remain milder than average in north-western Britain due to a warm south-westerly flow on the north-western flank of the high pressure. Sunshine amounts will be variable rather than plentiful, with some frost and fog overnight. However, widespread snowfalls are unlikely to occur during this period. The weather will tend towards becoming less settled again by the end of the period.
Mean temperatures will be about 2C above average in northern Scotland, but 1 to 2C below average over much of England, coldest relative to normal in the south-east. It will generally be drier than normal but a wet end to the period may raise rainfall totals close to the long-term average in most western districts. Sunshine totals are likely to be close to normal in the east and rather above normal in Wales and most western parts of England, but with considerable local variations depending on how long overnight fog takes to clear.