So, a foehn wind, as it turns out, is the warm and dry wind coming off the leeward side of a mountain.
(Windward, into the wind. Leeward, with the wind.)
So, for example, cool and wet air hits the front of a mountain range. Clouds form and rain out most of the air’s moisture as the air get higher and higher. Then warm and dry air falls back down the other side of the mountain.
Many of the islands of Hawaii are good examples of this: Half the island looks like a rain forest, the other half looks like a desert.
Good-grief, my allergies?
I’ll take the warm and dry side of the mountain.
The Santa Ana, which is named for one of the canyons it rushes through, is a foehn wind, like the foehn of Austria and Switzerland and the hamsin of Israel.
-Joan Didion, Slouching Towards Bethlehem