I assume you're referring to the -5 stretching across the Atlantic?
Originally Posted by: SEMerc
Not really, I have seen that happen in mega siberian blocks in the north; I am more refering to the -5C isotherm getting from a canadian or american source to the UK.
A figure of -6C or -7C is very unusual for a westerly source, so I am wondering if it is a record. Note anything from the arctic (even if it is on a westerly or SWerly) doesn't count, it has to originate from the american continent. I see two major barriors against this ever happening:
1) The atlantic very quickly moderates any cold air, despite the source being exceptionally cold (sometimes as low as -35C) even at the 850hpa level
2) Cold air crossing the atlantic is ascociated with cyclonic activity, so it is very hard to get a direct feed without the air being wrapped around lows and being forced over even more atlantic before it arrives in the UK; contrast this to a siberian esterly which, though unusual, can be direct.
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2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)
Total: 8 days with snow/sleet falling.
2022/2023 Snow days (approx 850hpa temp):
18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)
Total: 7 days with snow/sleet falling.
2021/2022 Snow days (approx 850hpa temp):
26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.