SEASONS
One warming number for the state hides four different ones inside the year.
Four seasons, four trends
MEAN TEMPERATURE BY METEOROLOGICAL SEASON, STATEWIDEThe warming page reports one number for the state's year. This page takes that year apart. All four meteorological seasons warm, and all four trends are statistically significant on the full 131-year record — there is no season California has kept.
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Winter here is December–February, credited to the year the January belongs to — so the winter of 1895 would need December 1894, which the record does not contain, and the winter series runs 1896–—. A season missing any month is excluded entirely, the same rule the annual statistics use.
The monthly fingerprint
A WARMING TREND FOR EACH CALENDAR MONTH ON ITS OWNTwelve separate trends, one per calendar month, each with its own autocorrelation-adjusted interval. This is the chart that says where in the year the warming lives — and the answer has consequences: the fastest-warming month of the twelve is September, which is the heart of the fire-weather window, when fuels are at their driest and the offshore winds begin.
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Season by season, division by division
28 TRENDS: SEVEN DIVISIONS, FOUR SEASONSThe statewide seasonal story is not uniform on the ground. The full grid is below, north at the top — every cell is positive, and the strongest column varies by division, which is a fact about geography rather than noise.
These are measured trends in one state's divisional record, with intervals wide enough to overlap in many places — the ranking of two seasons whose intervals overlap is suggestive, not established. Attribution of the pattern to specific mechanisms is a modelling question, and this site carries no model output.