Joliet climate

Joliet Frost Dates and Growing Season

NOAA 1991-2020 normals for Joliet, 3.4 km from Joliet, elevation 3838 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Joliet. 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 May 29 and the first fall freeze around September 15, a growing season of about 107 days.

Median at 36°F
last June 13, first September 4
Median at 32°F
last May 29, first September 15
Median at 28°F
last May 13, first September 26

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°FJun 30Jun 25Jun 20Jun 17Jun 13Jun 10Jun 7Jun 3May 30
32°FJun 17Jun 9Jun 4Jun 1May 29May 26May 22May 19May 14
28°FMay 31May 24May 19May 16May 13May 10May 8May 4May 1
24°FMay 14May 9May 6May 3Apr 30Apr 29Apr 26Apr 22Apr 17
20°FMay 5Apr 30Apr 27Apr 24Apr 20Apr 17Apr 14Apr 10Apr 6
16°FApr 28Apr 21Apr 17Apr 13Apr 10Apr 6Apr 3Mar 31Mar 24

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°FAug 22Aug 27Aug 30Sep 1Sep 4Sep 6Sep 9Sep 13Sep 17
32°FSep 1Sep 5Sep 9Sep 11Sep 15Sep 17Sep 21Sep 25Oct 1
28°FSep 11Sep 17Sep 20Sep 24Sep 26Sep 29Oct 1Oct 4Oct 9
24°FSep 22Sep 27Sep 30Oct 2Oct 5Oct 8Oct 12Oct 16Oct 21
20°FOct 1Oct 5Oct 10Oct 14Oct 17Oct 20Oct 24Oct 28Nov 1
16°FOct 10Oct 16Oct 20Oct 24Oct 27Oct 31Nov 3Nov 7Nov 12

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°F1019590858177726556
32°F127121116111107102989386
28°F153147142138134130126120113
24°F176168164160155152148143136
20°F199192187182177173168163155
16°F221213209203198194189182175

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
7,999
Cooling degree days, base 65°F
266
Growing degree days, base 40°F
3,556
Growing degree days, base 45°F
2,590
Growing degree days, base 50°F
1,788
Growing degree days, base 55°F
1,132
Growing degree days, base 60°F
620

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,30700
February1,11201
March96003
April704020
May4362121
June17426310
July38124552
August6397501
September27116230
October661047
November98704
December1,28800

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 3.4 km from Joliet. 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 USC00244506 (Joliet). Public domain.