Koochiching County climate

Koochiching County Frost Dates and Growing Season

NOAA 1991-2020 normals for Big Falls, 5.5 km from Koochiching County, elevation 1220 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Big Falls. 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 24 and the first fall freeze around September 20, a growing season of about 117 days.

Median at 36°F
last June 4, first September 9
Median at 32°F
last May 24, first September 20
Median at 28°F
last May 10, first October 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°FJun 27Jun 17Jun 11Jun 7Jun 4Jun 1May 30May 26May 22
32°FJun 6Jun 1May 29May 26May 24May 21May 17May 13May 6
28°FMay 28May 23May 18May 14May 10May 7May 3Apr 30Apr 27
24°FMay 17May 11May 6May 2Apr 30Apr 27Apr 24Apr 21Apr 17
20°FMay 6Apr 30Apr 26Apr 23Apr 20Apr 18Apr 15Apr 12Apr 7
16°FApr 25Apr 20Apr 17Apr 14Apr 11Apr 9Apr 6Apr 4Mar 31

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 25Aug 30Sep 3Sep 6Sep 9Sep 12Sep 15Sep 18Sep 22
32°FSep 6Sep 12Sep 15Sep 17Sep 20Sep 22Sep 25Sep 28Oct 3
28°FSep 17Sep 22Sep 25Sep 28Oct 1Oct 3Oct 6Oct 11Oct 16
24°FSep 29Oct 3Oct 7Oct 10Oct 14Oct 17Oct 20Oct 24Oct 30
20°FOct 11Oct 17Oct 20Oct 24Oct 27Oct 30Nov 2Nov 5Nov 9
16°FOct 23Oct 29Nov 1Nov 3Nov 5Nov 7Nov 9Nov 12Nov 17

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°F114108104999590857869
32°F13913212712211711310910497
28°F162156151146142137132127118
24°F185178173168164160156151144
20°F206199195191187182177172166
16°F223216213209205201198193186

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
10,140
Cooling degree days, base 65°F
176
Growing degree days, base 40°F
3,196
Growing degree days, base 45°F
2,327
Growing degree days, base 50°F
1,579
Growing degree days, base 55°F
959
Growing degree days, base 60°F
479

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,86100
February1,52700
March1,26503
April794017
May4278137
June15931327
July7272465
August10753412
September32611184
October734034
November1,19001
December1,67900

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 5.5 km from Koochiching 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 USC00210746 (Big Falls). Public domain.