Think its time for one of these threads. Ive been very generous with the bounds here, but I think its necessary to cover most reasonable possibilities. There is a small (say 10%) chance of snow even to lower levels tommorow if any cold air can advect from the north sea, before the band of precipatation clears. Thursday sees some polar maritime air mixing into our low, and precipatation on occluded fronts could again turn to snow, possibly more likely this time but still marginal. The friday to saturday period doesn't currently suggest anything in the way of snow, but I include it because of the nature of the frontal system. We have a strong ana warm front with southerly winds on its leading edge;it would not take much of an upgrade even now to make it cold enough to produce snow on its leading edge given that the cold air will only be half way across the north sea by then.
And now some rough snow checking bench marks:
850hpa temperature:
-3C: Strong ana warm front or evaporational cooling event
-4C: Well defined warm occlusion
-6C: Showers, cold occlusion or kata warm front
-7C: Cold front
-8C: Warm sector precipatation
500-1000mb thickness:
Roughly 534dam for Strong warm front, otherwise closer to 526dm. Highly variable.
850-1000mb thickness:
129.5dm is usually an excellent benchmark for wintryness. <129dm would be almost definately snow.
In evap cooling event may rise to 130dm.
Dewpoints:
Snow very unlikely if d.p >1.5C. Good benchmark is 0C in general.
2m temp
If the 2m temp is 0.0C or lower, check 925mb temp; if this is significantly above 0C expect rain or freezing rain.
If the 925mb is around 0C then ice pellets, freezing rain or snow.
if 925mb is below 0C then snow.
If 2m temp is above 0C then very rough benchmarks:
1.5C: Frontal based precipatation
3C: Showers that come from the north sea
5C: Showers from a strong NWerly wind in winter
8C: Showers from a strong NWerly wind in spring
Soundings
Provided by the GFS and WRF from meteociel or weatheronline.co.uk. Limited range and accuracy but more obvious whether rain or snow likely from size of warm layer.
Twitter: @QuantumOverlord (general), @MedicaneWatch (medicane/TC stuff)
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.