Rolette County climate

Rolette County Frost Dates and Growing Season

NOAA 1991-2020 normals for Belcourt Keya Radio, 10.1 km from Rolette County, elevation 1960 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Belcourt Keya Radio. 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 19 and the first fall freeze around September 24, a growing season of about 126 days.

Median at 36°F
last May 30, first September 14
Median at 32°F
last May 19, first September 24
Median at 28°F
last May 9, first October 2

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 21Jun 10Jun 5Jun 1May 30May 27May 23May 20May 16
32°FJun 1May 28May 25May 21May 19May 16May 14May 10May 5
28°FMay 24May 19May 15May 12May 9May 6May 4May 1Apr 28
24°FMay 17May 10May 6May 4May 1Apr 30Apr 26Apr 22Apr 16
20°FMay 7May 2Apr 30Apr 26Apr 23Apr 19Apr 16Apr 13Apr 9
16°FApr 30Apr 23Apr 20Apr 17Apr 14Apr 11Apr 8Apr 5Apr 1

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 1Sep 5Sep 9Sep 12Sep 14Sep 17Sep 20Sep 23Sep 27
32°FSep 10Sep 14Sep 18Sep 21Sep 24Sep 26Sep 28Oct 1Oct 5
28°FSep 18Sep 24Sep 27Sep 29Oct 2Oct 4Oct 7Oct 11Oct 16
24°FSep 28Oct 1Oct 4Oct 8Oct 11Oct 14Oct 17Oct 20Oct 24
20°FOct 5Oct 10Oct 14Oct 17Oct 20Oct 23Oct 27Oct 30Nov 3
16°FOct 13Oct 19Oct 23Oct 27Oct 30Nov 1Nov 3Nov 7Nov 11

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°F12511911310910499958978
32°F143138134130126122117112105
28°F163157152148143140136131125
24°F182175169164160155151146139
20°F200193187183179175170164155
16°F217210205201196192187182175

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
10,015
Cooling degree days, base 65°F
279
Growing degree days, base 40°F
3,421
Growing degree days, base 45°F
2,547
Growing degree days, base 50°F
1,783
Growing degree days, base 55°F
1,139
Growing degree days, base 60°F
632

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,81600
February1,54000
March1,30801
April800019
May4198143
June14442352
July48118535
August7095490
September29816210
October735132
November1,19300
December1,64400

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 10.1 km from Rolette 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 USC00320626 (Belcourt Keya Radio). Public domain.