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Behind a deepening low pressure system, temperatures should initially drop below average.

Atlantic weather systems will then bring milder air for much of this forecast period but colder and drier interludes are still possible.

Trending milder

A deepening area of low pressure will move across southern and south-eastern parts of the UK on Wednesday, bringing spells of quite heavy rain to those parts, accompanied by stronger winds.

Further north, spells of showers are possible, which could turn wintry on higher ground. Temperatures should fall below average. Meanwhile, a temporary high pressure ridge is likely to move over parts of the UK, bringing some drier and calmer weather across the UK along with a frosty Wednesday night.

However the ridge of high pressure will then move away eastwards allowing areas of low pressure to start influencing the weather more, gradually bringing more unsettled weather from the west. As winds turn south to south-westerly so the temperatures will climb above average.

Ups and downs in temperature

Low pressure systems could move across parts of the UK at the beginning of next week leading to a cooler or colder north-west or even northerly flow behind, although the details are still subject to a greater degree of uncertainty. Drier and calmer conditions are possible soon after, related to transient high-pressure over parts of the UK.

The high pressure is likely to be rather short-lived due to a fairly active North Atlantic pattern that could continue through the rest of the week. Therefore stronger winds and wet weather are on the table at times. Temperatures may be slightly above average, with brief colder phases or fluctuations.

Consistent with this, the long-range weather forecast models suggest wetter, windier and milder conditions. This will likely lead to low pressure systems passing over parts of the UK with a risk of disruptive weather at times.

Unsettled and perhaps milder

There is only a small amount of variability in weather patterns in the period ahead. A quite active and mostly mild North Atlantic pattern could continue over much of the UK meaning that spells of wind and rain are likely. Any high pressure influence would be rather temporary.

However there could be occasions when a colder north-westerly flow develops, consistent with the centre of low pressure moving towards the eastern North Atlantic. As a result, temperatures could be a little lower at times, especially in Northern Ireland and Scotland with a possibility of occasional wintry precipitation, even at lower levels.

The next outlook on Friday should provide a clearer picture for the next week and a slightly more confident trend for later. Since there will probably be greater fluctuations in temperature, further wintry spells are to be expected later in December.