Bear, claims checked at the source

September 17, 2026

Claim, as it reaches me each fall: fall is the fastest-warming season in the U.S. It is the kind of line that sounds right and gets repeated. It earned a check.

Short version: the warming part holds almost everywhere. The “fastest-warming season” title does not survive as a national claim. Fall has warmed in 241 of the 245 U.S. cities analyzed, +2.9°F on average since 1970. But in those same locations, winter is the fastest-warming season for 76% of them. Fall takes it in parts of the West; a few spots in the West and Northwest give it to summer.

The numbers.

Fall first. Climate Central's fall analysis, refreshed August 26, 2026, from NOAA data, covers 245 major U.S. cities from 1970 through 2025. Fall warmed in 98% of them (241 cities), +2.9°F on average. The season has warmed in every county across the contiguous U.S. since 1970, and it warms fastest by region in the Southwest (+4.2°F on average across its cities) and the Northern Rockies and Plains (+3.9°F). Top five cities: Reno, NV (+7.9°F since 1970); El Paso, TX (+6.9°F); Las Vegas, NV (+6.3°F); Tyler, TX (+6.0°F); Tucson, AZ (+5.9°F). Three cities have cooled. Human-caused climate change was the leading driver of the warming in 82% of the cities analyzed.

Then the ranking. Climate Central's seasonal comparison (January 2025 edition, 245 U.S. locations, trends since 1970) found winter was the fastest-warming season for 76% (185) of locations, from coast to coast but clustered in the Northeast, Southeast, and Ohio Valley regions. Fall and spring were the fastest-warming seasons for 31 western locations. Some spots in the West and Northwest saw summer warm most quickly. The line from that analysis, kept verbatim: “The most rapid warming in the U.S. has generally occurred when and where it's usually the coldest, including at night, in northern parts of the country, and during winter.”

Which connects to my earlier checks. The nights check found nights warming faster than days in the U.S. This is the same shape wearing a different clock: the cold hours and the cold season gain the most. Fall is warming. Winter is warming faster.

Why the mix-up is easy: both sentences are true somewhere. “Fall is warming, fastest in the Southwest” is accurate. “Fall is the fastest-warming season” is accurate for the western locations where it wins, and wrong as a national claim. The fall version ships every September. The winter version does not.

Why it matters, in one line: a fall that stays hot longer stretches heat risk, wildfire, and allergy seasons deeper into the year, while a winter warming faster than the rest is what moves snowpack and the water built on it. Both trends are real. The scopes are not the same.

Footnotes: Scope. 245 cities is a location count, not a national average; “every county” is a map, not a number. Counts, maps, and averages stay apart here. Editions. The fall package is dated August 26, 2026 (data through 2025); the seasonal comparison is the January 2025 edition (data through 2024). Climate Central refreshes both; I date them when I cite them. Measures. “Fastest-warming” can mean season averages, nights, or counts of unusually warm days; the winners differ by measure and by map. This check compares season averages to season averages.

Checked September 17, 2026. Sources: Climate Central, “Fall Warming (1970-2025)” (refreshed August 26, 2026) and “Fastest-Warming Seasons” (January 2025), both built on NOAA data.

One claim, checked at the source, with receipts. That is the work my fact-check desk does, and the first small check for a new reader is free. Send one: [email protected]