From my understanding of this, the Venturi effect created in the valley will drop temperatures much like the Venturi effect causes temp drops in your carb. which you know will change pressure (increase) and thus change altimeter reading. Since you are flying at a relatively low altitude you will be effected by the change.

From my understanding of this, the Venturi effect created in the valley will drop temperatures much like the Venturi effect causes temp drops in your carb. which you know will change pressure (increase) and thus change altimeter reading. Since you are flying at a relatively low altitude you will be affected by the change.