Grundy County climate

Grundy County Frost Dates and Growing Season

NOAA 1991-2020 normals for Trenton, 5.1 km from Grundy County, elevation 837 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Trenton. 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 20, a growing season of about 184 days.

Median at 36°F
last April 27, first October 11
Median at 32°F
last April 16, first October 20
Median at 28°F
last April 6, 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 9May 5May 2Apr 30Apr 27Apr 24Apr 21Apr 18Apr 13
32°FApr 29Apr 25Apr 21Apr 19Apr 16Apr 13Apr 10Apr 6Apr 3
28°FApr 21Apr 16Apr 12Apr 8Apr 6Apr 3Apr 1Mar 29Mar 22
24°FApr 12Apr 6Apr 3Mar 31Mar 29Mar 25Mar 20Mar 16Mar 10
20°FApr 4Mar 31Mar 26Mar 22Mar 18Mar 14Mar 11Mar 7Mar 2
16°FMar 27Mar 20Mar 16Mar 12Mar 9Mar 6Mar 3Feb 28Feb 22

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 26Oct 1Oct 4Oct 7Oct 11Oct 13Oct 16Oct 19Oct 23
32°FOct 5Oct 11Oct 15Oct 17Oct 20Oct 22Oct 25Oct 28Nov 1
28°FOct 16Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 5Nov 11
24°FOct 25Oct 30Nov 1Nov 4Nov 7Nov 10Nov 13Nov 18Nov 25
20°FNov 3Nov 7Nov 12Nov 15Nov 18Nov 22Nov 26Nov 30Dec 5
16°FNov 12Nov 17Nov 21Nov 25Nov 29Dec 2Dec 5Dec 9Dec 15

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°F183177172168165161156152145
32°F204198193188184180176171165
28°F225217212208204200196191184
24°F248240234229224220216210203
20°F267260254249244240236230222
16°F290279273266262256251246238

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
5,679
Cooling degree days, base 65°F
1,258
Growing degree days, base 40°F
6,056
Growing degree days, base 45°F
4,847
Growing degree days, base 50°F
3,765
Growing degree days, base 55°F
2,807
Growing degree days, base 60°F
1,971

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,22300
February97906
March740247
April39311158
May13290429
June11269708
July1399863
August3329790
September73136515
October34322209
November710136
December1,07103

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 5.1 km from Grundy County. 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 USC00238444 (Trenton). Public domain.