Wilmington climate

Wilmington Frost Dates and Growing Season

NOAA 1991-2020 normals for Channahon Dresden Isl Dam, 15.1 km from Wilmington, elevation 505 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Channahon Dresden Isl Dam. 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 16 and the first fall freeze around October 26, a growing season of about 191 days.

Median at 36°F
last April 30, first October 15
Median at 32°F
last April 16, first October 26
Median at 28°F
last April 5, first November 6

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 14May 9May 5May 2Apr 30Apr 25Apr 22Apr 19Apr 15
32°FMay 3Apr 27Apr 22Apr 19Apr 16Apr 13Apr 11Apr 7Apr 3
28°FApr 19Apr 14Apr 10Apr 7Apr 5Apr 3Mar 31Mar 27Mar 20
24°FApr 9Apr 4Apr 1Mar 30Mar 26Mar 23Mar 19Mar 13Mar 8
20°FMar 31Mar 26Mar 21Mar 18Mar 14Mar 11Mar 8Mar 4Feb 27
16°FMar 21Mar 16Mar 12Mar 9Mar 5Mar 3Feb 28Feb 23Feb 17

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 1Oct 6Oct 10Oct 13Oct 15Oct 18Oct 21Oct 24Oct 28
32°FOct 13Oct 18Oct 21Oct 23Oct 26Oct 29Oct 31Nov 3Nov 8
28°FOct 24Oct 29Nov 1Nov 3Nov 6Nov 9Nov 12Nov 16Nov 23
24°FNov 2Nov 7Nov 10Nov 13Nov 16Nov 20Nov 23Nov 27Dec 1
20°FNov 8Nov 13Nov 18Nov 22Nov 26Nov 29Dec 1Dec 6Dec 12
16°FNov 15Nov 22Nov 26Nov 30Dec 3Dec 7Dec 11Dec 16Dec 21

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°F186181177172169165161156148
32°F211205199195191188184179172
28°F234227222217214211206201194
24°F259251245240236231226220215
20°F277270265260256250246240231
16°F296289283278273269264259251

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
5,976
Cooling degree days, base 65°F
954
Growing degree days, base 40°F
5,546
Growing degree days, base 45°F
4,375
Growing degree days, base 50°F
3,332
Growing degree days, base 55°F
2,407
Growing degree days, base 60°F
1,612

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,26101
February1,02002
March819234
April4506119
May17459358
June27195618
July2310773
August5250710
September70112493
October35519191
November705030
December1,08604

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 15.1 km from Wilmington. 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 USC00111420 (Channahon Dresden Isl Dam). Public domain.