Thursday 24th December 2020

So it’s Christmas Eve and it is actually cold. What a strange year this has been – a cold spell near Christmas, how unusual. And this cold spell will last into the start of January too.

Quite an unusual winter set-up and it has been for a while. Most winters we have a well-organised polar vortex, generally close to Greenland, with a strong jetstream bringing lots of low pressure systems from west to east.

This December we have a very disorganised polar vortex, with the strongest part and strongest ribbon of jetstream on the opposite side of the earth to us. The Atlantic is quiet – blocked with high pressure reaching into Greenland.

And this means that we now have a northerly flow, and this will be set in for a couple of weeks. No deep cold close enough to our north to tap into, so things cold but marginal in terms of snow, at least for us in lowland southern Britain.

I would be surprised if we don’t see snow falling at some point in this cold spell, and significant, disruptive snowfall is within the realms of possibility – but won’t be forecasted until closer to the time. I think I can forecast 4 days tops at the moment in terms of details. After that is just general theme (cold) and potential frost/fog/snow/sleet/rain.

Rather a long introduction – I don’t have any new photographs but I don’t think I’ve used this one from Paul yet. With a bit of luck, I might have some more seasonal photographs for next week’s forecasts.

So today will be cold in the northerly wind. Sunny spells, especially this morning, more cloud this afternoon but still some sunshine. A very small chance of a shower afternoon/evening, which could be wintry – but only a very small chance. 5’C at best. Wind fading overnight, fairly clear with a frost, down to around -2’C.

Christmas Day will be sunny but cold. Becoming a bit hazy in the afternoon but still bright. 4’C. Down to around -1’C at first in the evening, but temperatures ticking up gradually overnight as cloud thickens and the wind picks up, 5’C by dawn.

Boxing Day will be mostly cloudy and windy, with bits of occasional light (ish) rain – though dry much of the time. A little brightness at times also, and around 9’C. Wind continuing to strengthen overnight – gusts of over 50mph could cause some isolated damage. Rain becoming persistent and heavy too.

Sunday starts with heavy rain and strong winds – a bit of uncertainty over when this will clear, any time from 6am to midday. There is the potential for a squall line on the back edge, bringing a brief spell of very heavy rain, squally winds – possible hail/thunder also – the squall line element uncertain at this stage. Once this clears we’ll be looking at sunny spells and a small chance of a shower – which should still be of rain, if you catch one. 6’C but feeling colder. Frost possibly overnight, but this depends on the position of weather fronts.

And that is where my ability to provide details ends. So short, I know.

The general picture then is low pressure sat over the UK, with fairly cold air having filtered down from the north.

Weather fronts will move around the edge of the low, bringing a risk of more persistent rain, sleet or snow – but where they will be and when is impossible to know at this stage.

Other features will develop within the flow, bringing wintry showers too – but again this is too far out. I think we won’t know until around 24-48 hours before any particular day, what the chance of rain/sleet/snow is.

Until then, it is just potential.

Certainly it will be cold. Temperatures broadly in the range of 2’C to 6’C by day, with overnight frosts on the nights when we have clear skies.

Should we get a notable snowfall that settles, then this will reduce expected temperatures, and therefore feedback into an increased chance of further snow as the cold spell progresses. Freezing fog will also be possible – which could also mean daytime temperatures close to 0’C should this occur.

As I said earlier, I will be surprised if we don’t see snow falling at some point in this cold spell.

Right, I’m off to go enjoy the completion of my self-isolation period and buy some bread. And possibly wine.

I wish you all a Merry (ish) Christmas, or if you don’t celebrate Christmas then I wish you a pleasant extended weekend.

Next full forecast will be on Monday, but I’ll update you before then on any wintry potential when it becomes clearer…if it does!

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