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

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