It forms above the mountain range, usually at the beginning of a chinook wind as a result of orographic lifting over the range.
The effect is enhanced when the moving air mass is uplifted by the orographic effect of higher elevations on the downwind shores.
Because of orographic lift, precipitation increases with elevation up to 8000 ft where it slowly decreases to the crest.
Rainfall can be abundant at times, as mountains very close to the coast create an orographic effect.
Mechanisms of producing precipitation include convective, stratiform, and orographic rainfall.
Such heavy rainfall typically occurs on the island when tropical cyclones approach, owing to orographic enhancement in the mountainous interior.
There, the rains were enhanced by moist air rising over the mountain peaks and condensing, a process known as orographic lift.
Marked orographic enhancement over this terrain is evident on radar imagery.
