Aitkin County climate

Aitkin County Frost Dates and Growing Season

NOAA 1991-2020 normals for Aitkin 2E, 21.4 km from Aitkin County, elevation 1215 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Aitkin 2E. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around May 16 and the first fall freeze around September 28, a growing season of about 133 days.

Median at 36°F
last May 28, first September 19
Median at 32°F
last May 16, first September 28
Median at 28°F
last May 4, first October 8

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FJun 12Jun 7Jun 3May 31May 28May 26May 23May 20May 15
32°FJun 1May 27May 23May 19May 16May 13May 10May 6Apr 30
28°FMay 21May 14May 10May 7May 4May 1Apr 28Apr 24Apr 19
24°FMay 7May 1Apr 27Apr 24Apr 20Apr 18Apr 14Apr 10Apr 6
20°FApr 23Apr 19Apr 15Apr 12Apr 9Apr 7Apr 5Apr 2Mar 29
16°FApr 15Apr 10Apr 7Apr 5Apr 3Apr 1Mar 29Mar 25Mar 19

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 2Sep 8Sep 12Sep 16Sep 19Sep 21Sep 24Sep 27Oct 1
32°FSep 12Sep 18Sep 22Sep 25Sep 28Oct 1Oct 3Oct 6Oct 12
28°FSep 23Sep 28Oct 1Oct 4Oct 8Oct 11Oct 14Oct 19Oct 25
24°FOct 5Oct 9Oct 14Oct 18Oct 22Oct 26Oct 30Nov 2Nov 7
20°FOct 15Oct 23Oct 28Nov 1Nov 2Nov 5Nov 8Nov 12Nov 17
16°FOct 27Nov 1Nov 5Nov 8Nov 11Nov 14Nov 17Nov 21Nov 25

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F1321241191151121081049991
32°F155147142137133129124119112
28°F179172166161157152148141134
24°F205197191185181177172167158
20°F225218214209204200195190181
16°F239233228224220217213208201

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
9,141
Cooling degree days, base 65°F
270
Growing degree days, base 40°F
3,593
Growing degree days, base 45°F
2,670
Growing degree days, base 50°F
1,868
Growing degree days, base 55°F
1,192
Growing degree days, base 60°F
653

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,72200
February1,42500
March1,20602
April738020
May3907145
June11451390
July36117546
August6775473
September25719240
October645149
November1,05604
December1,48600

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 21.4 km from Aitkin County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00210059 (Aitkin 2E). Public domain.