Twin Cities slow to see the season's first freeze

Winter isn't just coming in the Twin Cities — it's a week overdue.

Minneapolis-St. Paul International Airport has yet to report the first fall freeze this year, though it is imminent as temperatures continue to drop into the 30s at night. Much of outstate Minnesota has already experienced its first frost, a sign that the growing season has officially ended.

Since 1960, the MSP airport has recorded an average first freeze date of Oct. 6. Outstate cities such as Rochester and International Falls fell within that range this year — albeit nearly a month later than they typically see frost on the ground — documenting a freeze Oct. 8. Duluth followed the next day, also past due.

Experts say it's hard to pinpoint what might cause such a delay in freezing weather. One factor might be the amount of precipitation Minnesota has had this year, which saturated the ground for nearly four months straight.

"When you have a lot of moisture, it's more conducive to keeping more heat in the soil," said Tony Zaleski, a meteorologist at the National Weather Service in Chanhassen. The Twin Cities collected nearly 8 inches of rain in August, nearly twice as much as a year ago.

The earliest reported freeze at MSP since record-keeping began in 1938 was Sept. 4, 1974. Since then, freeze dates have steadily pushed further into the season, landing in mid- to late October over five decades, according to a Star Tribune analysis of data from the Midwest Regional Climate Center.

Of the three outstate cities we analyzed — Rochester, International Falls and Duluth — Rochester consistently recorded later freeze dates than the others, including MSP, because it is the farthest south. International Falls, nearly 400 miles north of Rochester on the Minnesota-Canada border, broke its earliest freeze date record in 2004, documenting a frost on Aug. 22. The freeze date of Aug. 24 had previously held its record for nearly 30 years.

Outstate cities consistently freeze three weeks to a month, on average, before MSP. However, that was not the case this year.

The earliest MSP has ever recorded a freeze was Sept. 3, more than two weeks earlier than the next closest freeze date of Sept. 20. The latest frost date in the Twin Cities was Oct. 29, 1963. Forecasters say it is unlikely that we will keep the chilling weather at bay until Halloween this year, as there are active freeze warnings this week in Hennepin and Ramsey counties.

With freeze dates in what typically should still be summer for most of the state, International Falls experiences a significantly shorter growing season than the Twin Cities area. In certain years, that gap can stretch two months or more.

MSP's Sept. 3 record appears to be an outlier. It is earlier than the top three freeze dates from Rochester and the third earliest from Duluth. Minneapolis has not seen a freeze date remotely that early in more than 30 years. Minnesotans may not want the first freeze to land that early ever again, since it's a date that lands squarely at what most residents think of as the beginning of fall.