W COUNTRY: By Christmas Day & into early Jan, high pressure is set to dominate UK weather (ECMWF shown for 30/12, high cell position not to be taken literally!). However, this is likely to shift to Scandinavia further into Jan, with increasing risk of cold by mid-Jan on into Feb pic.twitter.com/LchctdRPJD

— Ian Fergusson (@fergieweather) 21 December 2018

Let's hope Mr Fergusson's thoughts are vindicated.

Depends when he said it. Saying it during one of the hottest Julys on record is a bit like getting a king on play your cards right and then shouting 'lower!'

UK Outlook for Thursday 27 Dec 2018 to Saturday 5 Jan 2019:

Generally quiet weather is expected to end the week, with high pressure to the southeast of the UK. A frontal system is likely to push from west to east across the north of the country on Friday, with some rain and possibly hill snow for Scotland, with colder weather following for a time. High pressure is likely to remain close by to the UK next weekend and into early January with generally settled conditions continuing. Occasional frontal systems across the north and west likely to bring some rain and possibly hill snow for Scotland, with clearer and showery conditions following. Any clear spells overnight will bring a risk of frost or fog. Temperatures generally staying on the mild side, but perhaps colder at times in the north.

UK Outlook for Sunday 6 Jan 2019 to Sunday 20 Jan 2019:

Generally quite settled and dry across the south with variable amounts of cloud and overnight mist and fog patches. Perhaps more changeable in the north with rain and stronger winds at times. Probably turning more widely unsettled for a time in early January with showers or longer spells of rain and stronger winds affecting all parts along with some hill snow in the north. By mid-month there is the increasing chance of colder weather, with the likelihood of frost, fog and snow, with these conditions probably continuing for the rest of the period. Despite the potential change to colder weather through mid-January, some milder, wet and windy interludes remain possible throughout the period.

https://www.metoffice.gov.uk/public/weather/forecast 

BBC monthly outlook

Summary

Dry for many to end December

Saturday 22 December—Sunday 30 December

Often cloudy and misty but dry in the south

This weekend, Saturday will be the drier and brighter of the two days for many with sunny intervals although the west and northwest of the UK will also have scattered showers. On Sunday, England and Wales will be mostly cloudy and wet with outbreaks of rain. Staying drier for much of Northern Ireland and Scotland, though, with some bright spells but a risk of fog both early and late in the day.

Next week will see a change in the weather as a high pressure area moves closer to the south of the UK. Many central and southern areas of the UK will have often dry and relatively calm weather, including on Christmas Day. However, it looks as though there could be a lot of cloud at times with a risk of mist and fog in places, particularly through the nights and into the mornings. Further north, it is likely to be breezier at times with occasional rain. Temperatures will mostly be a little above the December average although local night frosts cannot be ruled out, particularly in the south.

Monday 31 December—Sunday 6 January

Mostly dry and settled; possibly wetter later

Mostly dry and settled conditions are expected to persist into the first week of January, thanks to an area of high pressure often nearby to the south. However, the high pressure ridge will also bring the continued threat of fog at times, particularly to central and southern areas of the UK.

Cloud amounts are uncertain. The cloud may be thick enough at times to produce occasional drizzle. However, where any lengthier clearer periods develop, there is also likely to be some patchy night frost. Overall, temperatures are expected to be near to the normal for this time of year. In the far-north, temperatures are favoured to be a little above the seasonal average with more of a breeze and a lower risk of fog. Towards the end of the week, we may see high pressure move further away to the south, bringing an increasing chance of wetter and breezier conditions then.

Monday 7 January—Sunday 20 January

Breezy and wet. Mild at first, then colder.

In the second week of January, we expect somewhat breezier and wetter conditions compared to the first week. Low pressure areas are likely to move closer to the UK at times, bringing rain and brisk winds at times. The risk of fog will become much lower too. Temperatures are likely to be variable but, on average, a little above the normal for this time of year.

Into the third week of January, we expect low pressure areas to still be close to the UK, continuing to bring unsettled and breezy conditions at times. However, low pressure areas could well start to track further south across the UK. Therefore, the wettest conditions are favoured to be over the southern half of the UK. Over northern areas of the UK, it should turn less wet but somewhat colder at times. Indeed, there looks to be an increasing chance of some snow at times for northern areas of the UK. The main uncertainty to this forecast is on the extent of colder air by the middle of January; there is a considerable risk that significantly colder conditions extend to many areas by then.

Next Update

Could we see colder weather arriving from the north for the middle of January?

https://www.bbc.co.uk/weather/outlook

UK Outlook for Friday 28 Dec 2018 to Sunday 6 Jan 2019:

The last few days of December see high pressure lying to the south of the UK. On Friday settled, cloudy conditions prevail in the south, whilst a band of rain and possibly some hill snow spreads eastwards across northern areas. This will followed by colder, clearer showery weather by Saturday. A similar pattern is likely into the first week of the New Year, with generally settled weather conditions predominating, especially in the south, but with occasional bouts of strong winds, rain and hill snow across the north and northwest, followed by colder, showery conditions. Where skies clear overnight there will be an increased risk of frost and fog. Temperatures generally mild to start, but trending downwards as we go into January.

UK Outlook for Monday 7 Jan 2019 to Monday 21 Jan 2019:

The second week of January will probably be settled and generally dry across the south, with variable amounts of cloud and overnight mist and fog patches. In the north there may be more changeable weather at times, with occasional wet and windy weather bringing a risk of gales and hill snow. By mid-month there is a greater chance of colder weather, with a increasing likelihood of frost, fog and snow, with these conditions probably continuing for the rest of the period. Despite the potential change to much colder weather during mid-January, some milder, wet and windy interludes remain possible throughout the period.

https://www.metoffice.gov.uk/public/weather/forecast 

So, both BBC and Met Office now making the same predition about the threat of very cold weather by mid-Janaury:

BBC:

The main uncertainty to this forecast is on the extent of colder air by the middle of January; there is a considerable risk that significantly colder conditions extend to many areas by then.

Met Office:

By mid-month there is a greater chance of colder weather, with a increasing likelihood of frost, fog and snow, with these conditions probably continuing for the rest of the period. 

Still with a level of uncertainty that you'd expect at this range, but interesting that two forecasting bodies are seeing a high risk of similar trends.

Beat you too it Gavin :P

https://www.metoffice.gov.uk/public/weather/forecast

Outlook for the UK over the next 6-30 days

UK Outlook for Saturday 29 Dec 2018 to Monday 7 Jan 2019:
The last few days of December will see high pressure affecting the UK, so it should stay largely dry and cloudy here. However, wind and rain is likely across parts of the north at times, especially on Saturday. By New Year's Eve most areas should be largely dry with variable amounts of cloud and the best of the sunshine is likely in the south. However some fog patches could form where the skies clear, and possibly linger through the day in some areas. A similar pattern is likely into the first week of the New Year, although there are signs that more unsettled conditions could arrive later in the period. After a mild start, especially in the north, temperatures will probably return to near normal with night frosts at times.

UK Outlook for Tuesday 8 Jan 2019 to Tuesday 22 Jan 2019:
The second week of January will probably be settled and generally dry across the south, with variable amounts of cloud and overnight mist and fog patches. In the north there may be more changeable weather at times, with occasional wet and windy weather bringing a risk of gales and hill snow. By mid-month there is a greater chance of colder weather, with an increasing likelihood of frost, fog and snow, with these conditions probably continuing for the rest of the period. Despite the potential change to much colder weather during mid-January, some milder, wet and windy interludes remain possible throughout the period.

Updated: 15:06 on Mon 24 Dec 2018 GMT

UK Outlook for Sunday 30 Dec 2018 to Tuesday 8 Jan 2019:

On both Sunday and New Year's Eve there's a chance of rain across parts of the north and northwest, but there'll also be a good deal of dry weather, especially in the south although here some fog may linger through the day. Windy in the north, and generally mild. Similar conditions are expected on New Year's day, and the same pattern is likely to predominate during the first week of January. Any bouts of wet and windy weather are most likely to be confined to the north where there could be some hill snow, with a risk these unsettled conditions may spread further south at times. It will be mild for many at first, with temperatures trending slowly downwards across the south with an increasing risk of frost.

UK Outlook for Wednesday 9 Jan 2019 to Wednesday 23 Jan 2019:

The second week of January will probably be settled and generally dry across the south, with variable amounts of cloud and overnight mist and fog patches. In the north there may be more changeable weather at times, with occasional wet and windy weather bringing a risk of gales and hill snow. By mid-month there is a greater chance of colder weather, with an increasing likelihood of frost, fog and snow, with these conditions probably continuing for the rest of the period. Despite the potential change to much colder weather during mid-January, some milder, wet and windy interludes remain possible throughout the period.

https://www.metoffice.gov.uk/public/weather/forecast 

It's Getting to look a lot like Winter.......