Mahnomen climate

Mahnomen Frost Dates and Growing Season

NOAA 1991-2020 normals for Mahnomen, 0.2 km from Mahnomen, elevation 1212 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mahnomen. 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 7 and the first fall freeze around September 28, a growing season of about 143 days.

Median at 36°F
last May 19, first September 19
Median at 32°F
last May 7, first September 28
Median at 28°F
last April 29, 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 5May 31May 26May 22May 19May 16May 13May 10May 5
32°FMay 24May 18May 14May 11May 7May 5May 2Apr 30Apr 27
28°FMay 12May 7May 3May 1Apr 29Apr 27Apr 24Apr 20Apr 15
24°FMay 2Apr 29Apr 25Apr 22Apr 19Apr 17Apr 14Apr 10Apr 6
20°FApr 23Apr 19Apr 16Apr 12Apr 10Apr 7Apr 5Apr 2Mar 30
16°FApr 16Apr 12Apr 8Apr 6Apr 4Apr 2Mar 31Mar 28Mar 22

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 3Sep 9Sep 13Sep 16Sep 19Sep 21Sep 24Sep 27Oct 1
32°FSep 15Sep 19Sep 23Sep 26Sep 28Oct 1Oct 4Oct 7Oct 13
28°FSep 23Sep 29Oct 2Oct 5Oct 8Oct 13Oct 16Oct 19Oct 25
24°FOct 3Oct 9Oct 14Oct 17Oct 21Oct 24Oct 28Nov 1Nov 4
20°FOct 14Oct 21Oct 25Oct 29Nov 1Nov 2Nov 5Nov 8Nov 14
16°FOct 25Oct 30Nov 2Nov 4Nov 6Nov 9Nov 12Nov 15Nov 19

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°F14013312912512111711310798
32°F161154150146143139133129122
28°F182176171166162158154149142
24°F204198192188184180176171162
20°F222216211207203199194189182
16°F236229224220217213210204198

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
9,470
Cooling degree days, base 65°F
362
Growing degree days, base 40°F
3,768
Growing degree days, base 45°F
2,854
Growing degree days, base 50°F
2,046
Growing degree days, base 55°F
1,353
Growing degree days, base 60°F
782

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,81800
February1,50100
March1,24603
April724024
May34120208
June10570417
July34128559
August58106513
September24835261
October656459
November1,14602
December1,59500

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 0.2 km from Mahnomen. 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 USC00215012 (Mahnomen). Public domain.