McHenry County climate

McHenry County Frost Dates and Growing Season

NOAA 1991-2020 normals for Crystal Lake 4NW, 8.4 km from McHenry County, elevation 940 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Crystal Lake 4NW. 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 25 and the first fall freeze around October 22, a growing season of about 179 days.

Median at 36°F
last May 5, first October 11
Median at 32°F
last April 25, first October 22
Median at 28°F
last April 12, first November 1

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 21May 15May 11May 8May 5May 2Apr 30Apr 27Apr 23
32°FMay 9May 4May 1Apr 28Apr 25Apr 22Apr 19Apr 16Apr 11
28°FApr 27Apr 22Apr 19Apr 15Apr 12Apr 10Apr 7Apr 4Mar 31
24°FApr 15Apr 10Apr 7Apr 4Apr 2Mar 31Mar 27Mar 22Mar 17
20°FApr 4Mar 31Mar 28Mar 24Mar 21Mar 19Mar 16Mar 12Mar 7
16°FMar 28Mar 22Mar 18Mar 16Mar 13Mar 10Mar 6Mar 3Feb 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 25Oct 1Oct 5Oct 8Oct 11Oct 14Oct 16Oct 19Oct 24
32°FOct 7Oct 13Oct 17Oct 19Oct 22Oct 25Oct 27Oct 30Nov 4
28°FOct 20Oct 25Oct 28Oct 31Nov 1Nov 4Nov 7Nov 10Nov 15
24°FNov 1Nov 4Nov 7Nov 10Nov 12Nov 14Nov 17Nov 21Nov 26
20°FNov 7Nov 11Nov 15Nov 18Nov 21Nov 24Nov 27Dec 1Dec 5
16°FNov 13Nov 19Nov 23Nov 26Nov 29Dec 2Dec 5Dec 10Dec 16

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°F178171166162157153149143135
32°F198191187183179176170164158
28°F220214210206202198193189181
24°F246238232228224220216212206
20°F266260254249245241236230223
16°F285278272268263259254248239

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
6,520
Cooling degree days, base 65°F
771
Growing degree days, base 40°F
5,045
Growing degree days, base 45°F
3,932
Growing degree days, base 50°F
2,948
Growing degree days, base 55°F
2,091
Growing degree days, base 60°F
1,361

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,30600
February1,09900
March883222
April513276
May21951318
June31162580
July5261720
August11215669
September12173404
October4045141
November780018
December1,14801

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 8.4 km from McHenry 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 USC00112048 (Crystal Lake 4NW). Public domain.