On Jan 19, 5:05*pm, Alan wrote:
On the 12Z GFS run the following chart shows cold air at the 850mb
level upstream of the UK *but not advecting very successfully. Is this
because of some damming affect caused by the alps? Would it also
explain the low relative humidities [air being forced over a mountain
range] similar to what happens when air cross the rockies in the US?
Or am I just letting my imagination run away and its simply because
pressure is rising and thus causing the air to descend and warm?

Cheers

Alan

http://www.wzkarten3.de/pics/Rmgfs1802.gif

Cold air advection goes with a backing wind with height up through the
troposphere.
Especially evident behind the cold front of a well-behaved mid-
latitude depression moving from the N.Atlantic.
However in this case, the arrangement of the temperature field appears
to be limiting cold advection. At least for the moment.

Len Wood
Wembury