After a snowy day for much of the country, later we go back into clearer skies in the south and east which will lead to an extreme cold night.
The reason tonight will be so much colder is because we have light winds and quite a few areas have snow lying on the ground – the perfect recipe for very low temperatures, but what difference does snow make?
Think of the ground as a radiator, it absorbs energy throughout the day which it receives from sunlight, and then radiates this at night. On a night with snow cover on the ground, this heat can be trapped from escaping into the air – a bit like your loft insulation stops the heat from escaping into your attic. This means that on a clear still night the air cools and is not then moderated by a little warmth from the ground so it can get extreme.
Also on clear calm nights we can get a nocturnal inversion developing which is where the ground gets colder than the air higher up and this traps the cold air at the surface and stops it from mixing with the warmer air above to again moderate the temperature – so again our surface gets colder, especially in glens and valleys. It’s in these situations we get our coldest nights and is the reason we record extremes in places such as Braemar and Balmoral and in the glens of the north Highlands such as Altnaharra and Glascarnoch.
That’s how it works, but what about tonight then? Well I think one of the cold spots will be around East Renfrewshire, Loudon and Doon Valley area with lows of -10C possible here. These are also the nights when Glasgow Airport in Renfrewshire can record some very low temperatures given it sits at the bottom of the valley, so here I wouldn’t be surprised to see -10C by Wednesday morning. Even the centre of Glasgow could be around -7C, which really doesn’t happen very often.
The Clackmannan and Falkirk area also looks like it could be another low spot with temperatures ranging from -6C to -10C. Edinburgh city centre may be closer to -5C, not quite as cold as Glasgow because the cloud will take a bit longer to clear away from here during Tuesday evening.
And of course, the Highlands will be one of the coldest areas with lows around -15C. I expect either tonight or in the next few nights somewhere may come close to -20C given the persistence of the cold and the continuation of fresh falls of snow.
Will any records be broken, well looking at Ayrshire first of all, I’d say it’s definitely up there as one of the coldest January nights, but Dalry hit a low of -15.5C in January 1982 and Kilmarnock -12C in January 1979, and those look safe for now.
Renfrewshire has also had even more extreme lows in the past with -16C recorded in Renfrew in January 1945.
So while it’s unlikely that many records, if any, will be broken in the next few nights it’s still very extreme, even by January standards.
The all-time record for January in Scotland is -27.2C, recorded at Braemar in 1982.
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