Paul Ward, Cumbernauld weather forecaster, gives us his latest thoughts on weekend weather, and explains the trickiness of getting it right.
The Complexity of forecasting snow.
Any weather forecaster will tell you how difficult it is to forecast snow in the UK. There are many finite variables that have to come together for snow. Right now we have a low pressure system to the West and a High pressure system to the East which are meeting over the UK.
The high in the East is trying to give us cold dry easterly air from Siberia which gives us bitterly cold, frosty, but dry days and nights with clear skies. The low in the west is trying to give us warm wet air from the Atlantic which if not blocked by the high, would give us a winter similar to last year where we had gales and rain but mild air in January.
So far, the high pressure has been winning giving us cold but sunny days, and early this week all models indicated that the high pressure would continue to win the battle until Saturday or Sunday, but current computer models indicate that the low pressure is going to creep slightly to the East.
This is where it becomes difficult to forecast snow. Computer models don’t easily take into account how stubborn cold air is. Cold air is dense and hard to shift so when warm wet air moves in, the cold air sits there and slows the advancing warm air. As the warm moist air hits the cold dry air it turns to snow but it is hard to say how far east it would advance. It could advance right across Scotland but there’s a possibility that it could advance as far as Falkirk and West Lothian but then stall leading to large accumulations in Cumbernauld. On the other hand, it could stall at the Campsie fells and we would see no more than a slight dusting and decent sunny spells as the stalled front weakened.
At the time of writing this (Wednesday) the Met Office have a yellow warning for snow in Cumbernauld and much of the UK. Due to the complexities of forecasting snow, this warning could escalate to amber, or be removed completely so check travel reports and local news before making any journeys on Friday.
My current revised forecast is — Friday, sunny spells in the morning but cloud developing in the afternoon. Snow will arrive around 5PM which will drift in strong winds and gusts up to 30mph from the east. Temperature will be -2C but feeling like -8C in the wind. Snow will continue through the night and into Saturday morning but should clear by 10AM. Sunny spells will develop but with temps at 0C, accumulations of about 20cm of snow will not thaw. A clear night will see the temperature drop to -4. Sunday should have lots of sunny spells but with the brisk easterly wind and snow already on the ground, the temperature will be at 0C but feel like -3C. Monday and Tuesday look like being a
repeat of Sunday but snow could return on Wednesday.
Paul Ward, Cumbernauld Weather forecaster
visit www.cumbernauld-weather.co.uk for live weather and stats.