First freeze dates delayed by nearly a month over 5 decades

Fall temperatures are rising across the United States. As a result, the season’s first freeze is now arriving weeks later — in some places, even over a month later than it did in the past.

Warmer falls, later freeze dates

It’s no surprise that fall seasons have been trending warmer over the past 50 years, with the Twin Cities warming by more than 5 degrees since 1970.

We’ve experienced warmer fall seasons in recent years, especially over the past four years when the average temperature from September through November exceeded 50 degrees.

With warmer falls comes the delay of our first freeze dates. In 1970, the first freeze typically occurred in late September to early October, but now it’s arriving nearly a month later.

Climate Central analyzed first freeze dates in 204 U.S. cities from 1970 to 2024. It found that in 88 percent of those cities, the first freeze had been delayed by an average of 12 days. Some of the most significant delays were in Reno, Nev., with a 41-day shift; Bend, Ore., with 38 days; and Santa Maria, Calif., with 35 days.

The ripple effects of a delayed first freeze

A delayed first freeze triggers a series of changes that impact many areas. One of the most immediate impacts is on allergy sufferers, as pollen and ragweed stick around much longer into the fall.

Minnesota, known for its stunning fall foliage, may also see changes. Warmer nights, which contribute to a delayed freeze, can mute our vibrant colors. For more details on how weather affects fall foliage, check out this article from the Minnesota Department of Natural Resources.

Later freezes are disrupting agriculture by changing when planting and harvesting take place. Meanwhile, our pesky unofficial state insect, the mosquito, is hanging around much longer and overstaying its welcome.