BBC monthly outlook
Summary
A mild end to 2018, but cooler in the New Year.
Saturday 29 December—Sunday 6 January
Often dry in the south, rain at times in the north
A ridge of high pressure will remain close to or over the south of the UK this weekend and into next week. Central and southern areas of England should be relatively dry and calm, although there will be a risk of mist and fog forming overnight and lingering into the following day. The north of the UK, being furthest from the centre of the ridge of high pressure, will see more changeable weather. This weekend is a good example of this, as strong winds and showers or longer spells of rain expected to affect Scotland, Northern Ireland and some parts of northern England and Wales on Saturday and at first on Sunday.
The first half of next week will see a similar pattern. Rain could affect some parts of Scotland on Monday and on Tuesday, although most places will be dry if rather breezy for the New Year's Eve celebrations on Monday evening. The rest of the UK should have a dry start to the week, but may remain rather cloudy and dull.
The second half of the week is likely to see high pressure remaining close to or over the UK, so we expect a continuation of the relatively dry weather. However, there will be a chance of showers and rain affecting the west or north-west of the country as Atlantic weather systems try and push eastwards. Finally, the current weekend will be very mild for the time of year, but temperatures are likely to gradually fall to nearer normal next week, albeit remaining a little above normal in many areas.
Monday 7 January—Sunday 13 January
Wetter and windier, with temperatures near normal
The most likely weather pattern for the first full week of January is for things to become more unsettled, wetter and windier than it has been of late. The ridge of high pressure which has been responsible for the recent relatively calm weather will slowly decline southwards into Europe, this allowing Atlantic fronts to push eastwards across the country. Although there is uncertainty in the detail of when the Atlantic fronts will arrive, over the week as a whole it does look likely that most parts of the UK will see rainfall near or a little above normal for the time of year. It also looks a little windier than average in most areas.
Temperatures will probably be near normal, perhaps a little bit above normal for central and eastern England and a little cooler than normal for Scotland. The main alternative to this scenario is that the ridge of high pressure will be slower to decline and could linger close to the UK. This would mean that the weather remains drier and less windy in the south, but wetter and windier for the north, particularly Scotland. It would also remain milder than normal too.
Monday 14 January—Sunday 27 January
Breezy and wet. Probably becoming colder.
In our last outlook, we mentioned the possibility of it becoming colder during the middle or end of January. This is mainly due to developments in upper atmosphere over the North Pole. We are currently seeing significant changes in the wind circulation pattern and temperature of the stratosphere over the Arctic. These kinds of changes are associated with an increased risk of cold weather over parts of the Northern Hemisphere around 2-3 weeks later. But before we get to the colder weather, we expect the middle of the month to be unsettled with rainfall at or above average and with the potential for some windy weather too.
Temperatures are likely to be near or perhaps a little below normal at this stage. The last full week of January is when we are likely to see an increased chance of cold north-easterly winds affecting the country. Temperatures are likely to dip below normal for the time of year, and this will bring an above average risk of snow. Of course, there is still some uncertainty and there is a chance that we will see Atlantic low pressure systems continuing to move eastwards across the country right through to the end of the month. If this happens, it is unlikely to become as cold, but will remain wetter and perhaps windy.
Next Update
Could colder weather still be on the way as we move through January?
https://www.bbc.co.uk/weather/outlook