THE SEVEN DIVISIONS
A statewide average for California describes nowhere in California. These do better.
What a climate division is
AND WHY THIS SITE USES THEMNOAA divides each state into regions of broadly similar climate — for California, seven of them, drawn largely on drainage basins. They are the smallest unit for which a continuous, homogenised monthly record reaches back to 1895, which is what makes them the natural grain for a site about the record. They are also the same seven the companion weather site names, so a division here and a division there are the same polygon.
It is not a place, and it is not always even a region. A county whose area straddles two divisions is assigned to one of them by its centroid, so a division is a set of whole counties that need not be contiguous — CA-3 is Alpine, Lassen and Mono, which arrive on the map above as three separate pieces with CA-2's Plumas and Sierra lying between them. Division CA-2 contains both the Sacramento Valley floor and the Cascade slopes that drain into it. A divisional average is a real quantity computed over that whole area, and no single town experiences it. For the climate of a place — one station, named, with its distance and elevation given — the companion site Golden State Weather carries 57 of them against the 1991–2020 station normals. The two datasets are never mixed.
Where they are
DERIVED FROM NOAA'S COUNTY MAPPINGNOAA does not publish division outlines — it publishes which counties belong to which division. These polygons are built from that mapping and public county boundaries, which is why the county lines are drawn inside them: a division is its counties, and showing that is the difference between a shape and an explanation.
The register
ONE ENTRY EACH, NORTH TO SOUTHSeven records, side by side
ONE STRIPE PER YEAR, NORTH TO SOUTHThe same stripe field as the front page, drawn seven times on a common scale. Each division is measured against its own twentieth-century baseline, so the colours compare departures rather than temperatures — a stripe of the same red means the same anomaly on the north coast as in Death Valley, which is what makes the seven readable against each other at all.