Monday 21st December 2020

Well I hoped you all got through that emotional roller-coaster of a weekend intact. And the weather is going on a bit of a roller-coaster this week – mild and wet at first, then cold, sunny and frosty – with a northerly plunge after Christmas. Snow possible.

Thanks to Jade for the photograph – though only the bottom half is representing the next few days.

This evening sees some showery rain – the odd heavy burst possible. Remaining cloudy overnight, still the odd shower and some drizzle, around 10’C.

Tuesday morning should see some brightness, though the odd splash of light rain around. Generally cloudier in the afternoon with patchy rain becoming more extensive – not especially heavy and still rather showery. Around 10’C. Cloudy with occasional showery rain overnight, 11’C.

Wednesday is when things start to become interesting with low pressure approaching from the south-west and deepening over us – with a large area of high pressure to the west blocking the Atlantic.

Spells of heavy rain will push up from the south and the rain band will stall somewhere across the south/central UK and intensify – becoming very heavy. The peak could be around the M4 kind of area, or perhaps a bit further north over the Midlands – which could mean the difference between 20mm of rain (a fair amount) or something closer to 40mm which would cause localised flooding issues.

The rain then clears south-east overnight, with winds becoming strong too. Mild during the day at around 13’C but slowly cooling down later and overnight – 4’C by dawn. There is a very, very small chance of some back-edge sleet/wet-snow as the rain clears overnight, but a very, very small chance.

So Christmas Eve (also my freedom from self-isolation day…yeah I received the dreaded notification) sees a northerly wind.

Any early cloud will quickly clear to be replaced by sunshine – but cold in the fresh northerly wind at 4’C. There is around a 25% chance of a shower or two in the flow, they could be of rain – or sleet/snow. Clear and frosty overnight, down to around -2’C.

Christmas Day will be fairly sunny but cold. Some cloud around and the wind will be lighter but still a notable northerly breeze. We should squeeze 4’C. Frosty at first in the evening, down to around 0’C but picking up as cloud thickens during the night, ending up around 4’C.

Boxing Day looks mostly cloudy, windy with some occasional bits of rain – though mostly on the light side. A temporarily milder flow from the west, around 8’C. Rain becoming more persistent and heavy in the evening – perhaps very heavy for a spell overnight. Around 6’C.

Sunday sets the scene for the next few days – low pressure having moved down from the north bringing cold air with it, and hanging around the UK for a few days. Not entirely dissimilar to early this month – except this time temperatures are lower and snow could fall at times – though still very marginal for the south of the UK as to whether it will be rain, sleet or snow, and very easily we could see varying precipitation types during this period.

Details very much subject to change from here, but currently Sunday looks dry with some sunny spells – a small chance of a shower. Around 5’C. Frosty overnight, down to around -3’C with freezing fog possible.

Monday will be colder, with maximum temperatures around 3’C. Suggestions of an area of rain/snow moving down from the north, but track is uncertain let alone whether it will be rain or snow.

In fact it is impossible to give details any further.

It will stay cold. Daytime maximums between 2’C and 5’C, with overnight frosts likely – unless there is cloud cover.

There is a good chance of snow falling at some point. Settling? Well, less confident on that matter. As I mentioned earlier, at times is could be rain, at times snow – maybe it will all be snow – but maybe it will all be rain.

It is far too marginal a call right now, a week away. But it certainly looks more seasonal than it has in years.

The cold weather is likely to stay for the first part of January, roughly first week. Mild and wet is likely to replace it with a more south-westerly flow, but cold blocks can take a bit of breaking down.

Looking further ahead – and further up, regular readers will know that I look for sudden stratospheric warming events during winter, which happen roughly every other winter, and give a good chance of significant cold spells within 2-4 weeks of an event. The Beast From The East in 2018 was a classic example.

I thought that there was a good chance of one this winter, and one is now being modelled for the beginning of January. No guarantee that it will happen, but stratospheric forecasting is more stable than our chaos down here.

And if it does happen – there is no guarantee that it will be strong enough to split the polar vortex (which is what cold/snow fans want), and then that the pieces fall in the correct places. But it looks promising – so that would mean a good chance of a significant cold spell during February, or perhaps even from late January.

We shall see. This winter is looking very different from recent winters…and yes I am still talking about the weather.

I will ignore any Christmas wishes tonight! As I will be back on Christmas Eve for definite…I will sadly still be in London. Which at least means you get a full forecast, probably in the morning though. I should join a Zoom call with the folks in the evening, even if I cannot sit next to my parent’s Christmas tree and slowly pick the needles off.

I wish you a pleasant few pre-Christmas days…and if you are prone to winter flooding then maybe keep an eye out on the usual websites like the Environment Agency. And keep a carrot handy in case you have the opportunity after Christmas to build a snowman.

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