De Witt climate

De Witt Frost Dates and Growing Season

NOAA 1991-2020 normals for Saint Charles, 21.4 km from De Witt, elevation 200 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Saint Charles. 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 March 17 and the first fall freeze around November 10, a growing season of about 238 days.

Median at 36°F
last March 31, first October 31
Median at 32°F
last March 17, first November 10
Median at 28°F
last March 5, first November 23

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°FApr 16Apr 9Apr 5Apr 2Mar 31Mar 26Mar 22Mar 17Mar 11
32°FApr 5Mar 31Mar 25Mar 21Mar 17Mar 14Mar 10Mar 5Feb 28
28°FMar 25Mar 17Mar 12Mar 8Mar 5Mar 1Feb 27Feb 21Feb 12
24°FMar 13Mar 6Mar 1Feb 26Feb 21Feb 15Feb 8Feb 1Jan 24
20°FMar 2Feb 23Feb 14Feb 6Feb 1Jan 27Jan 21Jan 14Jan 4
16°FFeb 19Feb 8Feb 1Jan 27Jan 21Jan 15Jan 10Jan 4Dec 30

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°FOct 17Oct 22Oct 26Oct 29Oct 31Nov 2Nov 5Nov 9Nov 16
32°FOct 27Nov 1Nov 3Nov 6Nov 10Nov 15Nov 19Nov 25Dec 1
28°FNov 4Nov 10Nov 15Nov 19Nov 23Nov 27Dec 1Dec 6Dec 14
24°FNov 16Nov 22Nov 28Dec 2Dec 7Dec 14Dec 22Dec 29Jan 5
20°FNov 29Dec 8Dec 18Dec 25Dec 30Jan 3Jan 8Jan 15Jan 28
16°FDec 14Dec 26Dec 31Jan 4Jan 7Jan 12Jan 18Jan 24Feb 4

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°F237229223218214210206201194
32°F264256249244238233227221213
28°F294283276270264258253247237
24°F332317309302296288280271259
20°F365353343336331323314306293
16°F365365365365359351343335325

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
90% of years
16°F or colder
60% 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
3,050
Cooling degree days, base 65°F
1,974
Growing degree days, base 40°F
8,289
Growing degree days, base 45°F
6,728
Growing degree days, base 50°F
5,307
Growing degree days, base 55°F
4,036
Growing degree days, base 60°F
2,924

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January737031
February558257
March36914184
April14858370
May31197631
June0386835
July0491956
August0462927
September12280718
October14474404
November4008142
December652151

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 De Witt. 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 USC00036376 (Saint Charles). Public domain.