Cold Spell - Feb 7th to 13th 2021 - Technical Discussion

M.T. Cranium wrote: »

A reliable answer to the Thursday snow potential won't really be available until closer to the time (Friday morning? jk) ... but there's no particular trend towards or away from good snow potential in the most recent guidance. The basic concept of that potential is that milder air will meet enough resistance from cold air to be forced over top for long enough that there's a decent period of snowfall before the inevitable time where the front pushes through and there's no more over-running. A second warm front is likely to be embedded in the flow which would lead to a secondary maximum of precip later, all rain (but this applied with greater confidence to the western two-thirds of Ireland, there are still options where the cold air is so resistant that it never actually leaves before the over-running moves away to the north, to be followed by a second boundary event of some kind around Monday).

This can all change if the models pick up on either (a) less resistance, the cold high moving away to the east too far to offer much resistance), or (b) less warm air advection, the cold air winning out more decisively and keeping the milder air at bay. I don't think there's much chance of (b) but there is a significant chance of (a).

Also snow rates can be greater or lesser depending on the dynamics, maybe some would fall but not very much, with adequate time but rates too low, the outcome is not as good.

I am seeing a tendency for the cold block to start sliding south more to the east of Britain which we'll need to assess, part of the thinking about snow potential involves how cold it remains in Britain because by then, with a southeast flow established, the cold air being maintained in eastern Ireland needs to be reinforced by deeper cold in western Britain, otherwise, western Britain becomes the more ideal location for the snowfall.

Just a general note, if anything, the small amounts of snow being reported so far are a bit ahead of median expectations from model guidance, as I was hoping might be the case, so certainly on a good trend since tomorrow was always looking better than today.

I was following reports fairly closely in southeast England and the details there are interesting. Snow amounts have varied considerably, two areas seemed to do particularly well, one being east Kent (10-20 cm amounts) and the other being a coastal to 20 km inland stretch of east Anglia from Norfolk to Essex, 20-30 cm amounts reported locally there. Into parts of west Kent, east London and east Surrey, 5 cms about the best amounts reported, and gradually down to trace-2 cm coatings further west into Oxfordshire.

Results in the U.K. midlands and Yorkshire somewhat hit or miss, but some reports of thundersnow which could become the case in the Dublin area at times tomorrow, we shall see. Not that I'm saying thundersnow plus massive amounts of snow in this case, just thunder with whatever smaller amounts you might see. Local maxima tomorrow could be 10-15 cm in a few lucky spots. Average might be a lot closer to 2 cms.