Updated 10th December - Covering the period 17th December - 8th January
This period will be warmer than average overall, by up to 2C in south-east England but with most regions coming out between 1.0 and 1.5C warmer than normal. Significant cold spells look unlikely until after the New Year.
Rainfall totals are forecast to be below normal in the north and east of Scotland but above normal in most other parts of the UK, particularly in the west and south.
Sunshine totals are expected to be near to slightly above normal in most parts of the country, with generally dull weather early in the forecast period offset by above average sunshine late in the period.
This week will see Britain in a southerly flow sandwiched between low pressure over Iceland and high pressure over Scandinavia but it currently looks highly likely that Britain will stay influenced by the milder North Atlantic air masses for most of the week, with the colder continental air staying the other side of the North Sea. It will thus generally be mild, though with potential for temperatures to fall close to or just below normal towards the end of the week as low pressure may move out into the North Sea introducing a short-lived northerly or north-easterly outbreak.
Rain belts will push in from the south-west at times but will often struggle to progress into the north-east of the country, so we can expect above average rainfall for the south, especially south- west, of Britain, but below average rainfall in the north and east of Scotland. For most of the rest of the country rainfall totals will tend to be near or moderately above normal. Sunshine totals are likely to be significantly below normal in most parts of the country but near or above normal in the north of Scotland. There is potential for snowfall on high ground towards the end of the week but at low levels it is generally likely that all precipitation will be rain. Inland parts of northern and eastern Scotland could see some snow to low levels towards the end of the week but this is uncertain and there will probably not be widespread lying snow.
Overall, mean temperatures are expected to end up about 2C above the 1981-2010 long-term average over much of the country this week, with the positive anomaly greater by night than by day in most regions due to the excess cloud cover. In the south-west it will probably be nearer 1C above normal.
Westerly winds will dominate during this week bringing generally mild and changeable weather. Some short-lived polar maritime or arctic maritime outbreaks may bring some wintry showers to northern parts of the UK at times, so a white Christmas in terms of sleet/snow falling can't be ruled out at this stage, especially for northern Britain, but widespread lying snow over the Christmas period looks somewhat unlikely. It is also likely to be windy at times.
Mean temperatures will probably be about 2C above the long-term average again in southern parts of the UK, and perhaps nearer 3C above in the south-east, but nearer 1C above in most northern areas and in Northern Ireland. It will generally be wetter than average, though with uncertainty over the precise distribution of rainfall anomalies. Sheltered parts of the north-east may again see near or rather below average rainfall. Sunshine totals are expected to be rather up on those of the previous week, with most eastern parts of the UK seeing above average sunshine, and western areas tending to see near average sunshine.
A changeable westerly type is forecast to see in the New Year, with a continuation of the generally mild and wet weather, but as we head into early January there is an increasing chance of high pressure building to the west of the UK bringing quieter weather and significant potential for one or two northerly outbreaks.
As a result, temperatures for this period as a whole are most likely to be close to normal, with a mild start to the period being counterbalanced by generally colder weather later in the period. Rainfall totals are also likely to be close to normal for most, but with below average rainfall favoured for the south-west of the country. With a high likelihood of some reasonably clear polar air masses coming in from the north-west and/or north later in the week, sunshine is expected to be above normal for most of the UK, though with close to average sunshine more likely for the northern half of Scotland.
Monthly weather forecast
The month ahead forecast, written by Ian Simpson is updated once a week - every Monday. As with any longer term forecast, it's not possible to go into much detail and accuracy can tend to drop off toward the end of the period but it can still act as a very good guide to the weather during the upcoming month.