Naperville climate

Naperville Frost Dates and Growing Season

NOAA 1991-2020 normals for Wheaton 3 Se, 6.8 km from Naperville, elevation 680 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wheaton 3 Se. 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 27 and the first fall freeze around October 17, a growing season of about 173 days.

Median at 36°F
last May 8, first October 6
Median at 32°F
last April 27, first October 17
Median at 28°F
last April 16, first October 29

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 26May 21May 16May 12May 8May 5May 1Apr 28Apr 23
32°FMay 14May 8May 3Apr 30Apr 27Apr 24Apr 21Apr 17Apr 12
28°FMay 1Apr 26Apr 23Apr 19Apr 16Apr 12Apr 8Apr 5Mar 31
24°FApr 20Apr 15Apr 11Apr 7Apr 3Apr 1Mar 29Mar 24Mar 18
20°FApr 11Apr 4Apr 1Mar 29Mar 25Mar 21Mar 17Mar 12Mar 6
16°FMar 31Mar 26Mar 22Mar 17Mar 14Mar 10Mar 7Mar 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 22Sep 27Oct 1Oct 3Oct 6Oct 9Oct 12Oct 16Oct 22
32°FOct 1Oct 6Oct 10Oct 14Oct 17Oct 20Oct 25Oct 29Nov 2
28°FOct 12Oct 18Oct 22Oct 26Oct 29Nov 1Nov 3Nov 7Nov 14
24°FOct 25Oct 31Nov 2Nov 5Nov 8Nov 12Nov 16Nov 19Nov 24
20°FNov 4Nov 8Nov 12Nov 16Nov 19Nov 22Nov 26Nov 30Dec 5
16°FNov 12Nov 18Nov 22Nov 26Nov 29Dec 2Dec 5Dec 10Dec 18

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°F171164159154150146141136128
32°F194187181177173168163158151
28°F217211205200195191186180173
24°F244235229223218214209204196
20°F265257251245240235230224216
16°F287279273267261255248243234

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
938
Growing degree days, base 40°F
5,513
Growing degree days, base 45°F
4,341
Growing degree days, base 50°F
3,294
Growing degree days, base 55°F
2,373
Growing degree days, base 60°F
1,585

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,24600
February1,01802
March807029
April44810120
May18262355
June31202621
July2291753
August6251710
September81108479
October35415188
November722034
December1,08004

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 6.8 km from Naperville. 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 USC00119221 (Wheaton 3 Se). Public domain.