Ag Weather Forum

So far this fall season, harvest and fieldwork have largely been done in freeze-free conditions in the United States. That's not a rare occurrence anymore. A study of the first freeze occurrence by Climate Central finds that since 1970, the first freeze by and large arrives later in 204 U.S. cities reviewed. The study is based on open-access temperature data from the National Oceanic and Atmospheric Administration (NOAA).

Out of the 204 cities reviewed in the contiguous U.S., the date of the first freeze is later in 88% (179) of those 204 cities. On average, the first fall freeze now arrives 12 days later than in the early 1970s. This change is not surprising when one considers how the fall season temperatures have changed. Except for a handful of counties in the Midwest and Southeast, fall warming covers the entire Lower 48 states. Warming is especially notable in the northern Midwest, Great Plains, Southwest, Intermountain West and the Northeast. In these regions, fall temperatures are 3-4 degrees Fahrenheit (or more) higher than they were in the early 1970s.

A look at the cities representing central U.S. crop areas finds that the first freeze arrives mostly one to two weeks later than back in 1970. That's significant. Later-arriving freezes mean longer active seasons for pests; a longer period for allergies; and for many fruit crops, lower yields because of reduced chilling dates. On the other hand, later-occurring fall freezes can give corn and soybeans an extended ripening timeline, which favors yields.

For the biggest delay in the first freeze date compared with 1970, it's hard to top what's happening in Reno, Nevada. The average first freeze in Reno has shifted from the third week in September back in 1970 to the first week in November now -- 41 days later or almost six full weeks.

This widespread delay in the occurrence of the first freeze has other warming-related company. Weather and climate agencies announced this week that September 2025 was the third warmest in recorded history, trailing Septembers of 2023 and 2024. Also, the United Nations World Meteorological Organization (WMO) reports that the atmospheric content of carbon dioxide -- the most prominent heat-trapping greenhouse gas -- reached a record level last year. Two other prominent greenhouse gases, methane and nitrous oxide, have also hit record levels according to the WMO.

The full Climate Central report on delayed fall freeze dates is available here: https://www.climatecentral.org/….

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Bryce Anderson can be reached at bryce.anderson@dtn.com

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