I’m thinking specifically of the eastern Sierra Nevada, eastern Washington & Oregon, and other parts of the Basin & Range.
Why does cold-weather precipitation cross those peaks but not warm?
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Cold air doesn’t hold as much water. So as moist air passes over mountain ranges and is pushed upwards, it tends to eventually fall out of the air. That might not be as it’s ascending but perhaps afterwards (on the eastern side in your examples). By the time what remains spreads out in to the wider, warmer, lower-elevation land afterwards, that air is able to hold the water no problem, and it doesn’t rain.
The way warmer air holds more water and how significant it is, is why weather services give humidity as “relative humidity” (the percent of water in the air relative to how much water air of that temperature/pressure *could* hold) instead of “absolute humidity” (how much actual water a unit of air is holding right now).
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