Snow and frost?! But it’s nearly May…
Last Thursday, the UK had its warmest day of the year so far, with 20.3C recorded at Porthmadog in north west Wales.
However, at the weekend, a plunge of cold air coming all the way from the Arctic sent temperatures plummeting to well below where they should be at this time of year.
April is renowned for providing a huge range of weather as warm air and cold air battle it out, but this chill is fairly impressive for so late in the month.
And there’s no let up in the cold weather this week, as a northerly wind continues to blow, bringing below normal temperatures, frosty nights and some snow.
Why so cold?
The cold weather we are seeing at the moment is actually linked to something that happened in early March, high up in the stratosphere at around 50km.
Something called sudden stratospheric warming took place, whereby a sudden large rise in temperature causes the wind to start blowing from east to west, rather than the normal west to east direction.
This reversal of wind direction then gradually feeds down in the atmosphere to the top of the troposphere, which is where our weather occurs.
The effect of this is to start to slow down or even reverse the direction of the jet stream, which determines the weather that we experience at the surface.
As the jet stream slows down, big, slow-moving blocking areas of high pressure tend to form, that sit in the same place for long periods of time.
One such area of high pressure has formed over the mid-Atlantic Ocean, feeding down this cold air all the way from the Arctic.
Cold all week
The universal theme for the weather across the UK this week is for temperatures to be 3-5C below normal for this time of year.
Daytime temperatures will be 4-9C in the north and 9-12C across the south – values more typical for the beginning of March.
At night, temperatures will widely fall close to freezing in towns and cities, with rural areas dropping as low as -5C locally, providing yet another week of annoyance for gardeners.
Snow in places
With the cold air comes the risk of some snow – mainly over the hills and mountains in the northern half of the UK.
However, in the heavier showers, there could be some sleet and hail mixed in almost anywhere, as cold air gets dragged down from aloft.
The Met Office has issued a yellow warning for snow and ice over northern Scotland during Monday and Tuesday, with 5-10cm possible over hills above 300m and a few centimetres possible at sea level.
During Monday night, there could even be a dusting over the hills in eastern coastal counties of England, but it would melt quickly on Tuesday morning in the strong April sunshine.
— Liam Dutton (@liamdutton) April 25, 2016
If you’re hoping to see the back of this cold weather, it’ll turn warmer next week, but temperatures will return to average, rather than anything impressive.