Forest Park climate

Forest Park Frost Dates and Growing Season

NOAA 1991-2020 normals for Chicago Midway AP, 11.6 km from Forest Park, elevation 612 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Chicago Midway AP. 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 11 and the first fall freeze around October 31, a growing season of about 201 days.

Median at 36°F
last April 23, first October 21
Median at 32°F
last April 11, first October 31
Median at 28°F
last April 1, first November 11

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 8May 3Apr 30Apr 26Apr 23Apr 20Apr 17Apr 15Apr 9
32°FApr 27Apr 21Apr 17Apr 14Apr 11Apr 8Apr 5Apr 2Mar 30
28°FApr 14Apr 9Apr 6Apr 3Apr 1Mar 29Mar 26Mar 21Mar 15
24°FApr 3Mar 31Mar 27Mar 24Mar 20Mar 17Mar 14Mar 11Mar 5
20°FMar 26Mar 21Mar 17Mar 14Mar 11Mar 8Mar 5Mar 1Feb 24
16°FMar 17Mar 13Mar 10Mar 6Mar 3Mar 1Feb 26Feb 21Feb 13

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 8Oct 13Oct 17Oct 19Oct 21Oct 24Oct 26Oct 28Nov 1
32°FOct 20Oct 23Oct 26Oct 29Oct 31Nov 2Nov 5Nov 9Nov 14
28°FOct 31Nov 2Nov 5Nov 8Nov 11Nov 14Nov 17Nov 21Nov 26
24°FNov 7Nov 11Nov 14Nov 17Nov 20Nov 24Nov 26Dec 1Dec 5
20°FNov 13Nov 18Nov 22Nov 26Nov 29Dec 1Dec 5Dec 10Dec 18
16°FNov 22Nov 27Dec 1Dec 3Dec 7Dec 11Dec 15Dec 21Dec 26

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°F198192188184180175172167159
32°F222215210205201196193188181
28°F246238234229225220217211204
24°F268260255250246241236231224
20°F286278272268263259254249240
16°F304296290284279275270263256

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
5,753
Cooling degree days, base 65°F
1,111
Growing degree days, base 40°F
5,787
Growing degree days, base 45°F
4,588
Growing degree days, base 50°F
3,526
Growing degree days, base 55°F
2,593
Growing degree days, base 60°F
1,786

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,20701
February98804
March788234
April4399123
May17871367
June24222648
July1353817
August3299761
September59136527
October33220205
November689035
December1,04504

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 11.6 km from Forest Park. 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 USW00014819 (Chicago Midway AP). Public domain.