If you think recent Septembers and early Octobers have been a lot warmer than you remember them being previously, you may be onto something!
Indeed, September of 2026 finished tied for the 10th warmest on record for the state, out of 132 years. Just one year earlier, September of 2025 had recovered from a significant early cold snap to finish as the eighth warmest on record. The warmest of all Septembers belongs to 2024, with a statewide average temperature of 65.1 degrees F and many stations in southern and central Minnesota reaching 70 F every day of the month for the first time on record. September of 2023 is the third warmest on record, thanks to an extraordinary heat event at the beginning of the month.
Meanwhile, early October has been no less stunning with its summer-like heat. Rare and record-setting 90-degree weather occurred in 2023, 2025, and 2026. Oddly, records for latest 90 F temperatures were set in 2023, only to be broken in 2025, and then broken again in 2026!
Thus, each of the last four Septembers had top or very high-ranking warmth and three of the last four Octobers had record-late heat waves. It's unusual to see similarly extreme conditions clustered in time like this given how our climate is defined by its variability, or its year-to-year "ups and downs." Even with well-documented warming of Minnesota's climate, the period from September into early October is an anomaly. So what is going on?
Some parts of this answer we simply do not know yet, but we do know that September is experiencing a remarkable warming trend, and this was true before the last four came in at or near the top of the charts. September is Minnesota's third-fastest-warming month: between 1970 and 2026 average September temperatures increased over six degrees F in Minnesota. Only January and December have greater warming, both adding over 8 degrees F since 1970. No month from February through October has even one-third of September's recent warming.
October's overall warming trend is less than half of September's, mostly because the middle and end of the month have, so far, had much more subtle warming than the first third or so of the month, which resembles the warming of September.
Additionally, early fall have showcased what we might call "summer creep," where daily temperatures typical for the middle of July get pushed later and later into fall, even into the final days of September or early October, resulting in bouts of unusually warm weather occurring at times when Minnesotans expect the cool, crisp air of autumn to take over.
Early October has recently begun notching new extremes of heat that had not been observed previously. September, however, has not (yet anyway) seen increases in its greatest heat extremes in recent years: the highest temperatures of the month have either fallen slightly or remained flat since 1970, and the number of 90F days have not increased in number at most stations. Instead, the month has seen sharp increases in very warm days that are not at or near record levels. For instance, the number of high temperatures reaching 70 F in September has doubled in much of northern Minnesota. So the hot weather season has expanded but has not intensified, and the basic extreme heat metrics for September have not changed, although the warm weather metrics clearly have.
Meanwhile, cool and cold weather metrics for September have dropped off dramatically. In central and southern Minnesota, the 2020s have had 75 to 90 percent fewer daily low temperatures reaching 32 F during September than the 1970-99 averages. In northern Minnesota, the same has been true for "hard freeze" days, with temperatures falling to 28 degrees or lower.
The warming of early fall can be seen on the landscape too. With consistent records since 1969, the date of peak fall color in Carver County is now about 13 days later on average than at the beginning of the record, shifting from early October, into the middle of the month. Other areas in Minnesota may have experienced different phenological changes, and the Carver County observations should be considered an example, rather than a representation of effects around the state.
October 12, 2026
KAB