In article ,
Will Hand writes:
GFS 06Z 13th is a warm outlier by 1-2 degrees at 850 hPa at critical
time at London. It was warm yesterday too c.f. UKMO.
That can make all the difference between rain/sleet/snow.
Even half a degree could be vital next week! Even the time the precip.
falls (night v day).
Sheesh I've seen some knife edges in my time, but ....

The uncertainty seems to be well illustrated by the apparently disparity
between the area that is covered by the latest weather warning and the
fact that the latest 3-5 day forecast for SE England (not covered by
that warning) says:

"Outlook for Monday to Wednesday:
Staying rather cold, although dry with bright or sunny spells on Monday.
Tuesday, sleet and snow is expected, with some accumulations possible.
Wednesday, outbreaks of lighter sleet or snow likely.

Updated: 1504 on Sat 13 Feb 2010"
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)