Regions of Oregon

Two million people live in the gap where the Columbia cuts the Cascades, and that gap is the weather. East wind out of the Gorge in December turns Willamette Valley rain into freezing rain on the east side while the west side stays wet and 40°F; the same wind in September brings the fires down the mountain. Ninety percent of the rain falls October to May, and almost none of it falls in July.

The valley is one long rain shadow with the Coast Range on one side and the Cascades on the other, and it collects what gets past both — 40 inches at Eugene, fog that sits on the floor for a week in January, and a July that can go 30 days without measurable rain. Up the Santiam and the McKenzie the same storms fall as snow, and in 2020 the same east wind that dries the valley took the fires down both canyons.