Cook County climate

Cook County Frost Dates and Growing Season

NOAA 1991-2020 normals for Grand Marais, 17.5 km from Cook County, elevation 612 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Grand Marais. 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 20 and the first fall freeze around October 5, a growing season of about 137 days.

Median at 36°F
last June 2, first September 26
Median at 32°F
last May 20, first October 5
Median at 28°F
last May 4, first October 17

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 18Jun 13Jun 9Jun 5Jun 2May 31May 28May 24May 19
32°FJun 6Jun 1May 27May 23May 20May 17May 13May 9May 3
28°FMay 20May 14May 10May 7May 4May 1Apr 29Apr 26Apr 21
24°FMay 6Apr 30Apr 28Apr 25Apr 23Apr 19Apr 16Apr 13Apr 8
20°FApr 23Apr 19Apr 16Apr 13Apr 10Apr 7Apr 5Apr 2Mar 29
16°FApr 16Apr 10Apr 7Apr 4Apr 2Apr 1Mar 29Mar 24Mar 18

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 12Sep 17Sep 21Sep 23Sep 26Sep 29Oct 1Oct 4Oct 8
32°FSep 22Sep 26Sep 29Oct 2Oct 5Oct 8Oct 11Oct 14Oct 20
28°FOct 1Oct 6Oct 10Oct 13Oct 17Oct 20Oct 24Oct 28Nov 1
24°FOct 15Oct 21Oct 24Oct 27Oct 30Nov 1Nov 4Nov 7Nov 12
20°FOct 26Oct 31Nov 2Nov 5Nov 7Nov 10Nov 12Nov 16Nov 21
16°FNov 1Nov 6Nov 9Nov 12Nov 15Nov 17Nov 19Nov 23Nov 28

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°F13412712211811411010610194
32°F159151146141137132128122113
28°F184177172167163159155149141
24°F208201197193189185181175168
20°F228222218214210207203198192
16°F244239234230226222218214209

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
9,763
Cooling degree days, base 65°F
53
Growing degree days, base 40°F
2,509
Growing degree days, base 45°F
1,681
Growing degree days, base 50°F
1,013
Growing degree days, base 55°F
523
Growing degree days, base 60°F
206

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,59500
February1,36600
March1,22100
April86702
May608025
June3731110
July16625326
August12423365
September3153167
October680019
November1,03500
December1,41200

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 17.5 km from Cook 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 USC00213282 (Grand Marais). Public domain.