On 21/11/10 21:40, Martin Rowley wrote:
... and another routine question that pops up about this time of year
(and in this situation) relates to thickness (500 - 1000 hPa variety)
*extremes*.

This is covered in the FAQ he-

http://weatherfaqs.org.uk/node/67

and by following the link at the bottom, you find a diagram giving an
'idea' of the extremes at a selection of locations for each month.
Note the caveats at the bottom.

The latest GFS run (12Z as I write this) out to T+180 has a large area
sub-512 dam across Wales, most of Scotland and large area of north&
central England. This would appear to be nudging the lower boundary of
those figures for November ... and the series would have included the
cold spells during November 1985 which, in some respects, is an
approximate analogue to the current set-up, though note that in that
month the *whole* month was cold, not just the latter third.

However, this is a long way off! Experience would suggest that models
tend to 'over-egg the pudding' particularly by 'over-advecting' model
cold air downwind - and of course we *are* dealing with the 'model'
atmosphere not the real one!

Tricky thing - reality.

Martin.



Out of interest, typically what surface temperatures, daytime and
nighttime would you expect for, say, a 510dam thickness assuming clear
skies? Can't remember experiencing a thickness that low before.