THE REGION ATLAS
Eighteen regions, cut on what actually sets the weather.
A region here is a piece of California that shares a cause, not a piece that shares a postcode. The North Coast is one region because everything in it is downwind of open ocean with a range immediately behind. The San Joaquin Valley is one because it is enclosed on three sides. The Eastern Sierra is separate from the Sierra Nevada — despite touching it — because a rain shadow is a different climate, not a variation on the one next door.
Every region below carries its terrain, its signature phenomena, all four seasons as they actually behave there, and every reporting place inside it with NOAA 1991–2020 normals. Hover the map to find one, or read down the list.
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How the cuts were made
Which side of the range
The single biggest control on California weather. Bishop and Blue Canyon are 90 miles apart and one gets under five inches a year while the other gets sixty-two. Any boundary that ignores the crest is describing something other than weather.
How far the marine layer reaches
The coast is not one strip. Half Moon Bay is in the ocean's air all summer, Livermore is 30 miles away and out of it entirely, and the boundary between them is sharp enough to be a region edge.
What the terrain does to a storm
Enclosure traps, escarpments dry, gaps accelerate and slopes lift. Regions that behave the same way under the same incoming system belong together, however far apart they look on a road map.