In article ,
Will Hand writes:

"John Hall" wrote in message news:$7iKTzBvlu
...
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"

The worded forecast is based on 12Z run, warning on an earlier run.
12Z runs seems to be 1/2 degree colder.

But the worded forecast is timed at 15:04, when the 12Z GFS wouldn't
have been available.

The current T+72 FAX (DT 13th 12Z) cf old T+84 FAX is interesting. Look
how much further south the 528 line is on 12Z run. Only about 50 miles
but it can make all the difference.
If this trend continues then we have "snowmageddon" for the south :-)


--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)