Decatur climate

Decatur Frost Dates and Growing Season

NOAA 1991-2020 normals for Dowagiac 1 W, 18.8 km from Decatur, elevation 740 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Dowagiac 1 W. 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 4 and the first fall freeze around October 11, a growing season of about 158 days.

Median at 36°F
last May 15, first September 30
Median at 32°F
last May 4, first October 11
Median at 28°F
last April 24, first October 26

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 31May 26May 22May 18May 15May 12May 8May 4Apr 30
32°FMay 22May 16May 11May 8May 4May 2Apr 29Apr 25Apr 21
28°FMay 10May 4Apr 30Apr 28Apr 24Apr 21Apr 18Apr 14Apr 10
24°FApr 30Apr 22Apr 18Apr 14Apr 11Apr 8Apr 5Apr 3Mar 30
20°FApr 14Apr 8Apr 5Apr 2Mar 31Mar 29Mar 25Mar 21Mar 15
16°FApr 4Mar 31Mar 29Mar 25Mar 22Mar 19Mar 16Mar 11Mar 4

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 15Sep 21Sep 24Sep 28Sep 30Oct 2Oct 5Oct 9Oct 13
32°FSep 27Oct 1Oct 5Oct 8Oct 11Oct 14Oct 17Oct 22Oct 27
28°FOct 8Oct 15Oct 19Oct 23Oct 26Oct 28Nov 1Nov 3Nov 7
24°FOct 23Oct 30Nov 1Nov 4Nov 6Nov 9Nov 12Nov 17Nov 22
20°FNov 4Nov 8Nov 12Nov 16Nov 19Nov 23Nov 27Dec 2Dec 7
16°FNov 13Nov 20Nov 25Nov 30Dec 2Dec 6Dec 10Dec 16Dec 22

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°F157150145140136131127122114
32°F180173167162158153149142135
28°F205198192186181177172167159
24°F231221216212208203198192185
20°F260250243238233228223218213
16°F281272266261256251246239231

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
6,729
Cooling degree days, base 65°F
583
Growing degree days, base 40°F
4,666
Growing degree days, base 45°F
3,582
Growing degree days, base 50°F
2,634
Growing degree days, base 55°F
1,811
Growing degree days, base 60°F
1,120

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28200
February1,09501
March937118
April560377
May26341276
June58131524
July16194643
August26148587
September14758368
October4626119
November780019
December1,10502

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 18.8 km from Decatur. 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 USC00202250 (Dowagiac 1 W). Public domain.