We had a pretty impressive upside down temperature profile over the UK this morning. 15C at Cassley in Northwest Highland (average is 7C) vs -4C at Frittenden, Kent and Bournemouth.
BBC Weather
Credit: Sean Batty
Southeast England started the day cold and frosty in clear, calm conditions beneath the high while the Northwest Highlands was positioned on the windier outer edge of the high. A trough over the North Atlantic and ridge over France, directed SSW winds clockwise around the high in NW Scotland.
While the air mass is mild relative to the time of year, The geography of NW Scotland allowed the foehn effect to kick in enhancing the warmth this morning at Cassley and across North Scotland. It’s all thanks to winds blowing up, over and down windward facing hills and as the air descends the leeside, the air compresses, dries and warms further.
GFS 500mb setup
Note the air stream connects the Azores with NW Scotland almost perfectly between trough and ridge.
Credit: Tropical Tidbits
GFS surface shows winds strongest ahead of the rain bearing front which was positioned just west of the Azores and Western Isles.
Credit: Tropical Tidbits
In the 850mb temp chart, note the narrow stream of very mild air running between the trough and ridge from Azores to Scotland.
Credit: Meteoceil
Here are the current temperatures as of mid afternoon.
Meteoceil
Weirdly Altnaharra was the warmest place and it appears Eskdalemuir in Dumfriesshire was coolest in the UK yesterday at 13.8C and 3.6C respectively.
Meteoceil
Mild across the north, cool across the south today but it’s opposite tomorrow thanks to a front slipping south.
Whilst it's mild in the north and chillier in the south today, we'll have a reversal of fortunes tomorrow pic.twitter.com/LbkU5Igz8j
— Met Office (@metoffice) December 19, 2017
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