Farmers’ Almanac Map Shows When the First Frost Hits Your State as Cold Air Moves In
The Farmers’ Almanac has released a map showing when that usually happens where you live. For a good part of the northern US, the average date and the current forecast now fall in the same week.
Cold Air Is Heading for the Northern Tier
The Climate Prediction Center’s week-2 outlook, issued September 10, shows a slight risk of much-below-normal temperatures over parts of the northern Plains, including the Upper Mississippi Valley and eastern Great Lakes, from September 18 to 20, and over northern New England from September 19 to 22.
Forecasters point out that near-freezing nights are not unusual for late September in those areas. They also note that any frost or freeze could still be “impactful to some vegetation and unsuspecting populations.”
Parts of the country have already had frost alerts. NWS Caribou issued frost advisories for northern Maine on September 8 and 9, with lows at 32 degrees, which is close to the Farmers’ Almanac average for that part of the state.
Where the First Frost Usually Lands
Alaska and the high country go first, with Fairbanks averaging its first frost around August 28 and Bozeman, Montana, around September 16.
Late September belongs to the northern Plains and Upper Midwest: Bismarck around September 23, Duluth around September 27 and Billings around October 1.
October covers the middle of the country, with Denver averaging October 7, Indianapolis October 15 and Chicago October 28. After that, it slides south to New York City on November 11, Atlanta on November 19 and New Orleans on December 5.
Parts of the country have already had frost alerts. NWS Caribou issued frost advisories for northern Maine on September 8 and 9, with lows at 32 degrees, which is close to the Farmers’ Almanac average for that part of the state.
Where the First Frost Usually Lands
Alaska and the high country go first, with Fairbanks averaging its first frost around August 28 and Bozeman, Montana, around September 16.
Late September belongs to the northern Plains and Upper Midwest: Bismarck around September 23, Duluth around September 27 and Billings around October 1.
October covers the middle of the country, with Denver averaging October 7, Indianapolis October 15 and Chicago October 28. After that, it slides south to New York City on November 11, Atlanta on November 19 and New Orleans on December 5.
Phoenix averages December 25 and Orlando January 6. Miami gets frost only in a severe cold snap, and Honolulu doesn’t get frost at all.
Frost and Freeze Are Not the Same Thing
A freeze is an air temperature of 32 degrees or lower, while frost refers to ice crystals that form on surfaces.
Frost is ice crystals forming on grass, leaves and car windshields. It can show up when the official reading is several degrees above freezing because the air at ground level is colder than the thermometer a few feet up. Clear, calm nights provide the conditions frost needs to form.
The Almanac divides cold temperatures into three categories. A light freeze at 29 to 32 degrees kills tender plants, a moderate freeze at 25 to 28 degrees damages many garden plants, and a hard freeze around 24 or colder takes out most unprotected vegetation.
One more thing worth knowing before you circle a date: the averages on the map are 50 percent probabilities, not deadlines. Frost had already arrived by that date in about half of recorded years, and an early cold front from Canada can bring it sooner than the average date. What happens after the frost is a separate forecast, and the Almanac’s zone-by-zone winter outlook covers that.
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