De Witt climate

De Witt Frost Dates and Growing Season

NOAA 1991-2020 normals for Clinton #1, 22.9 km from De Witt, elevation 585 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Clinton #1. 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 22 and the first fall freeze around October 16, a growing season of about 175 days.

Median at 36°F
last May 2, first October 6
Median at 32°F
last April 22, first October 16
Median at 28°F
last April 13, first October 25

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 17May 12May 8May 5May 2Apr 30Apr 27Apr 23Apr 18
32°FMay 8May 2Apr 29Apr 26Apr 22Apr 19Apr 17Apr 14Apr 9
28°FApr 29Apr 23Apr 19Apr 16Apr 13Apr 10Apr 8Apr 4Mar 31
24°FApr 18Apr 12Apr 8Apr 5Apr 2Mar 31Mar 28Mar 23Mar 17
20°FApr 6Apr 1Mar 29Mar 25Mar 21Mar 18Mar 14Mar 9Mar 4
16°FMar 28Mar 22Mar 19Mar 16Mar 13Mar 9Mar 5Mar 2Feb 26

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 23Sep 28Oct 1Oct 4Oct 6Oct 9Oct 11Oct 14Oct 18
32°FOct 2Oct 7Oct 11Oct 13Oct 16Oct 19Oct 21Oct 24Oct 28
28°FOct 11Oct 17Oct 20Oct 23Oct 25Oct 27Oct 30Nov 2Nov 5
24°FOct 24Oct 28Oct 31Nov 1Nov 4Nov 6Nov 9Nov 13Nov 18
20°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 16Nov 20Nov 24Nov 29
16°FNov 6Nov 11Nov 15Nov 19Nov 22Nov 25Nov 28Dec 2Dec 8

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°F174168164160156152148142134
32°F193187182179175171166161155
28°F215208204199195191186181175
24°F238230225220217213208203195
20°F260253247242238233228223216
16°F276269264259256251246240234

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
6,265
Cooling degree days, base 65°F
918
Growing degree days, base 40°F
5,468
Growing degree days, base 45°F
4,316
Growing degree days, base 50°F
3,282
Growing degree days, base 55°F
2,367
Growing degree days, base 60°F
1,576

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,33700
February1,08202
March819231
April4289131
May15968381
June19202633
July2292755
August8231688
September94101461
October38414173
November773026
December1,16102

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 22.9 km from De Witt. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00131635 (Clinton #1). Public domain.