According to the Weatherman

As I was saying, it rained most of Saturday afternoon on the western slope of Killington. The clouds were moving eastwards, and, as I understand it, rise into the cooler air of the mountain, and since cool air does not hold its moisture very well, it rains. There were intermittent showers further west in the valley, that is, Rutland, and over on the eastern slope of the mountain, but nothing relatively steady.

According to the Weatherman

As clouds ascend the slope,
things cool, and rain begins
to fall. Our gyroscope
turns east—the origins
of desert-dwelling monks
in dehydrated clothes
are artifacts of funks
the weather system blows
over the mountaintop.
It’s just environmental
prospects—nothing can stop
that wholly accidental.

The best example of this wet western slope phenomenon that I have seen is in Oregon. West of the Cascades, it’s a virtual rainforest. But east of the Cascades is literal desert.