Will, wouldn’t cold air from the west have to be cold thru
the depth, since there won’t be a surface inversion layer? I would guess
an 850mb temperature of -6c would produce at best a sleety mix. You
would need to go down to -8c before getting proper snow. Are we likely
to see such cold air from the
current set up?

Don't forget that cooling from latent heat effects will be pronounced at
times in these frontal battlegrounds, producing deep isothermal layers
around melting point - so rules of thumb using temperatures 5000 feet up in
the atmosphere need to be used with care.
--
Freddie
Bayston Hill
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/#!/BaystonHillWx for hourly reports