I have been following the GFS model - it has consistently forecast low
thickness values for Xmas day.
These persist for a further couple of days before warming takes place from
the SW. This is complicated by a further plunge of cold air for New Year,
albeit not as cold as over Xmas. Conditions look ripe for snow and very
cold conditions - negative day maximums over wide areas on Boxing day and
the 27th. The situation is not too different to 1981 when cold advection
took place from the Northwest with 510 DM air over the UK. Those of us that
can remember the set up in 1981 will remember the very deep snowfalls that
this situation produced.

Regards
Rob
Farsley

http://homepage.ntlworld.com/robert....3/Farsley.html

"ROBERT BROOKS" wrote in message
...
I have been following the GFS model - it has consistently forecast low
thickness values for Xmas day.
These persist for a further couple of days before warming takes place from
the SW. This is complicated by a further plunge of cold air for New Year,
albeit not as cold as over Xmas. Conditions look ripe for snow and very
cold conditions - negative day maximums over wide areas on Boxing day and
the 27th. The situation is not too different to 1981 when cold advection
took place from the Northwest with 510 DM air over the UK. Those of us
that
can remember the set up in 1981 will remember the very deep snowfalls that
this situation produced.

Regards
Rob
Farsley

http://homepage.ntlworld.com/robert....3/Farsley.html



Right on the limits of my memory that one. (I was only 8 years old)
I cant remember the synoptic situation, but I do remember Santa gave me a
plastic sledge that Xmas and I had several good winters out of it, before I
destroyed the plastic runners on a frost (rather than on snow) sometime in
1987.
Alex

ºººººººººººººººººººººººººººººººººººººººººººº
Alex Stephens Jr
Wishaw, North Lanarkshire, Scotland
N55º47'14", W3º55'15". 360ft/117m amsl
http://www.alex114.pwp.blueyonder.co.uk/
ºººººººººººººººººººººººººººººººººººººººººººº

"ROBERT BROOKS" wrote in message
...
I have been following the GFS model - it has consistently forecast low
thickness values for Xmas day.
These persist for a further couple of days before warming takes place from
the SW. This is complicated by a further plunge of cold air for New Year,
albeit not as cold as over Xmas. Conditions look ripe for snow and very
cold conditions - negative day maximums over wide areas on Boxing day and
the 27th. The situation is not too different to 1981 when cold advection
took place from the Northwest with 510 DM air over the UK. Those of us that
can remember the set up in 1981 will remember the very deep snowfalls that
this situation produced.

Regards

Exactly. I was forecasting in 1981 and I remember it well. 30cm level snow at
Heathrow.
That's part of the forecasting process of course, experience.

I've also seen slow moving baroclinic zones oriented NW-SE just to west of UK a
few times as well. These can produce some nasty surprises as warm front waves
run south bringing heavy snow to the east of them. Nightmare to forecast in
detail. IIRC the mild air often comes in slower than expected, hence caution is
required in warming things up too quickly after Boxing day.

Cheers,

Will.
--

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http://www.lyneside.demon.co.uk/Hayt...met_office.htm "
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"Will Hand" wrote in message
...

Snip
I've also seen slow moving baroclinic zones oriented NW-SE just to west of
UK a
few times as well. These can produce some nasty surprises as warm front
waves
run south bringing heavy snow to the east of them.

Talking of waves (T+96)
http://imkpc3.physik.uni-karlsruhe.de/pics/brack3.gif

Jon.

I have been following the GFS model - it has consistently forecast low
thickness values for Xmas day.

GFS has been consistently forecasting roughly the same scenario every run
since 17 December. Low to NE and High to SW bringing in very cold wind.
The only thing that has been changing is exactly the precise strength and
direction of the wind. The 528 dam line has also been slightly wobbling.
Wind direction has varied between W and NW and NNW.

I have been archiving the Christmas Day GFS runs every day...
http://www.djmurphy.demon.co.uk/christmas


I'm sure the runs for the next few days will see a similar scenario.


Brendan

Brendan DJ Murphy wrote:

I have been following the GFS model - it has consistently forecast low
thickness values for Xmas day.

GFS has been consistently forecasting roughly the same scenario every run
since 17 December. Low to NE and High to SW bringing in very cold wind.
The only thing that has been changing is exactly the precise strength and
direction of the wind. The 528 dam line has also been slightly wobbling.
Wind direction has varied between W and NW and NNW.

I have been archiving the Christmas Day GFS runs every day...
http://www.djmurphy.demon.co.uk/christmas


I'm sure the runs for the next few days will see a similar scenario.


One problem I have with GFS is that about a week ago one run, well into the
forecast, had a slow-moving old low over the northern North Sea with
thickness in its circulation averaging 528. Further in to the forecast, the
whole of the area of circulation of the low had thicknesses below 528. I
found it difficult to believe that a low sitting over the warm sea would
cool down in this way. In my experience the reverse is more likely.

Graham

"ROBERT BROOKS" wrote in message
...
I have been following the GFS model - it has consistently forecast low
thickness values for Xmas day.
These persist for a further couple of days before warming takes place from
the SW. This is complicated by a further plunge of cold air for New Year,
albeit not as cold as over Xmas. Conditions look ripe for snow and very
cold conditions - negative day maximums over wide areas on Boxing day and
the 27th. The situation is not too different to 1981 when cold advection
took place from the Northwest with 510 DM air over the UK. Those of us
that
can remember the set up in 1981 will remember the very deep snowfalls that
this situation produced.

Regards
Rob
Farsley

http://homepage.ntlworld.com/robert....3/Farsley.html




And in 1981 it lasted for over 3 weeks. This cold spell seems like just
another of these quickies. These have become common in the last 3 years. 2
or 3 days and thats your lot.

In article ,
Gavin Staples writes:
And in 1981 it lasted for over 3 weeks. This cold spell seems like just
another of these quickies. These have become common in the last 3 years. 2
or 3 days and thats your lot.

I think that such short spells always have been much commoner than the
long ones. It's just that it's only the long ones that we remember a
couple of decades afterwards.
--
John Hall
"It is a very sad thing that nowadays there is so little useless
information."
Oscar Wilde (1854-1900)

This is not necessarily a problem with GFS, but with using the
1000-500mb thickness as the determining factor of what is warm and
cold. Yes, the low would tend to warm out at the lowest levels, but if
the surface pressure is below 1000mb then I assume the model calculates
the negative 1000mb height using the standard formula. In addition, if
the cold advection aloft is rapid, then the height of the 500mb level
might be falling faster than the calculated 1000mb level is rising,
thus the thickness of the layer will continue to decrease temporarily.
I hope that makes sense.