Cass County climate

Cass County Frost Dates and Growing Season

NOAA 1991-2020 normals for Deep Portage, 7.3 km from Cass County, elevation 1471 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Deep Portage. 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 5 and the first fall freeze around October 5, a growing season of about 150 days.

Median at 36°F
last May 16, first September 25
Median at 32°F
last May 5, first October 5
Median at 28°F
last April 26, first October 18

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 30May 26May 23May 19May 16May 14May 11May 8May 4
32°FMay 19May 14May 11May 8May 5May 3May 1Apr 29Apr 24
28°FMay 8May 5May 2Apr 29Apr 26Apr 23Apr 20Apr 17Apr 12
24°FApr 30Apr 25Apr 22Apr 19Apr 16Apr 14Apr 11Apr 7Apr 4
20°FApr 21Apr 16Apr 13Apr 10Apr 8Apr 6Apr 3Apr 1Mar 26
16°FApr 14Apr 9Apr 6Apr 4Apr 2Mar 31Mar 28Mar 23Mar 17

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 20Sep 23Sep 25Sep 28Sep 30Oct 3Oct 6
32°FSep 22Sep 27Sep 30Oct 3Oct 5Oct 8Oct 11Oct 15Oct 20
28°FOct 1Oct 6Oct 10Oct 14Oct 18Oct 21Oct 25Oct 28Nov 2
24°FOct 13Oct 19Oct 24Oct 28Oct 31Nov 1Nov 5Nov 8Nov 13
20°FOct 26Oct 31Nov 1Nov 4Nov 6Nov 9Nov 12Nov 15Nov 20
16°FNov 1Nov 5Nov 8Nov 11Nov 13Nov 16Nov 18Nov 22Nov 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°F149142137133130127123119113
32°F170164159154150147143137131
28°F192186180176172168165159151
24°F214208203199195191186180175
20°F231224219215211208204199193
16°F244237232228224221217213207

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
8,802
Cooling degree days, base 65°F
398
Growing degree days, base 40°F
3,934
Growing degree days, base 45°F
2,983
Growing degree days, base 50°F
2,143
Growing degree days, base 55°F
1,428
Growing degree days, base 60°F
841

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,71600
February1,40300
March1,13902
April697135
May32118208
June8780443
July28161598
August45109528
September23229269
October616157
November1,05104
December1,46800

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 7.3 km from Cass 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 USC00212050 (Deep Portage). Public domain.