Willmar climate

Willmar Frost Dates and Growing Season

NOAA 1991-2020 normals for Willmar Wwtp, 1.7 km from Willmar, elevation 1100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Willmar Wwtp. 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 April 30 and the first fall freeze around October 7, a growing season of about 159 days.

Median at 36°F
last May 9, first September 29
Median at 32°F
last April 30, first October 7
Median at 28°F
last April 19, first October 19

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°FMay 23May 18May 15May 12May 9May 7May 4May 1Apr 27
32°FMay 13May 8May 4May 2Apr 30Apr 27Apr 24Apr 21Apr 16
28°FMay 2Apr 29Apr 25Apr 22Apr 19Apr 16Apr 13Apr 10Apr 5
24°FApr 24Apr 19Apr 15Apr 12Apr 10Apr 7Apr 4Apr 1Mar 27
20°FApr 16Apr 10Apr 7Apr 4Apr 2Mar 31Mar 28Mar 23Mar 16
16°FApr 9Apr 5Apr 2Mar 30Mar 26Mar 23Mar 19Mar 15Mar 10

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 16Sep 20Sep 23Sep 26Sep 29Oct 1Oct 3Oct 6Oct 11
32°FSep 23Sep 28Oct 1Oct 4Oct 7Oct 10Oct 13Oct 17Oct 21
28°FOct 2Oct 8Oct 13Oct 16Oct 19Oct 21Oct 24Oct 27Oct 31
24°FOct 15Oct 20Oct 23Oct 26Oct 29Oct 31Nov 2Nov 5Nov 10
20°FOct 24Oct 29Nov 1Nov 3Nov 5Nov 7Nov 10Nov 14Nov 19
16°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 15Nov 18Nov 21Nov 26

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°F160154150146142138134129122
32°F178172167163159156152148142
28°F200193188184179176171167160
24°F219212208204200197192187181
20°F235228223219215212208204197
16°F250243238234229226221216211

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
8,309
Cooling degree days, base 65°F
596
Growing degree days, base 40°F
4,411
Growing degree days, base 45°F
3,425
Growing degree days, base 50°F
2,547
Growing degree days, base 55°F
1,778
Growing degree days, base 60°F
1,123

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,65200
February1,37600
March1,11103
April637150
May27134262
June51136536
July10218673
August22151594
September17053345
October564481
November99606
December1,44900

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 1.7 km from Willmar. 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 USC00219004 (Willmar Wwtp). Public domain.