Often in Scotland, if the West coast is basking in sunshine then the East coast will be shivering in the Haar (sea fog). Today (Sept 2nd), it is the West coast underneath the damp cloud and the NE enjoying warm sunshine.
This is a fine example of the Fohn (Foehn) Effect. A weather setup resulting in warm strong and drier winds that descend in the lee of a mountain barrier. So for Scotland there is a fresh to strong Westerly this morning bringing low cloud and rain to Argyll and the NW Highlands. As the air is forced up over the Cairngorms and Grampians it cools and condenses, so it loses it’s moisture. Once over the mountains it warms up and as it is now drier, there is less cloud. The rate at which air cools and warms is different for dry and saturated air, so going up the mountain the cooling is less, than the warming of the dry air on the other side, for the same change in height.
The winds leaping off the mountains, can be very gusty on the lee(sheltered) side and can produce splendid cloud formations. Such as Lenticularis as the waves of air flow are set up downwind.
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