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