Milder with a north westerly wind?!
After the longest spell of cold weather so far this winter, all parts of the UK are set to have a milder week, with temperatures even a little above average for mid-February.
What may be surprising to hear is that the milder air is coming from the north west, which is usually renowned in the winter months for bringing cold air and frequent snow showers.
Before I get on to explaining why on this occasion it’s not the case, I just want to take a quick look back at the weekend, as it provided us with the coldest night of the winter so far.
Friday night saw Holbeach, Lincolnshire fall to -15.6C, beating the previous lowest temperature so far this winter of -12.4C at South Newington, Oxfordshire during the night of the 3rd February.
Saturday also saw the lowest daytime maximum temperature for this winter so far, with Coningsby, Lincolnshire reaching just -5.3C.
You may have read in the media reports of temperatures lower than this, but they weren’t recorded at official weather observation sites and therefore can’t be officially recognised by the Met Office.
Official weather observation sites have to meet a number of strict standards set by the World Meteorological Organization, which includes things such as regular maintenance and ensuring the equipment isn’t influenced by external factors that may affect readings.
Why was Friday night the coldest night of the winter so far?
It’s because all of the ingredients were present for the temperature to fall quickly and relatively far.
Thanks to high pressure, there were clear skies, allowing what little relative heat there was to escape into the atmosphere.
There was also a good covering of snow on the ground. Snow covered surfaces are more efficient at radiating any heat up into the atmosphere than ground without snow cover.
Finally, there was little or no wind, which stopped mixing of air in the lower atmosphere and allowed cold air to pool at the surface.
Turning milder with a north westerly wind?!
As I mentioned at the beginning of this blog, the week ahead is looking mild for all parts of the UK thanks to a north westerly wind – although a rather unusual one.
A true, classic north westerly wind brings polar maritime air towards the UK. This is an air mass that has polar origins, yet has travelled over the mid-Atlantic.
So it is cold, but has been warmed from below by the relatively warm Atlantic Ocean. This makes the air unstable and forms huge cumulonimbus clouds with heavy, wintry showers.
However, this week’s mild air has a very different origin. It has actually come from the Azores, albeit via a very long route. It has travelled northwards around an area of high pressure, brushed past Iceland, then sunk southwards across the UK.
What does the weather hold this week?
Well apart from being milder with a lack of frosty nights, the week ahead will be quite cloudy with occasional rain – particularly for the north west of the UK.
There will be some limited sunshine, but it could also be quite murky at times as the mild air moves over the still cold ground.
One thing that is certain this week is that any remaining snow will thaw and the picturesque, white landscape will become a memory.
Don’t forget, you can see just how mild it’s going to be where you are by visiting the Channel 4 Weather website. You can also join me for weather chatter on Twitter – @liamdutton