Blaine County climate

Blaine County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ft Belknap 2 Sw, 13.7 km from Blaine County, elevation 2527 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ft Belknap 2 Sw. 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 16 and the first fall freeze around September 22, a growing season of about 128 days.

Median at 36°F
last May 28, first September 12
Median at 32°F
last May 16, first September 22
Median at 28°F
last May 6, first September 30

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

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°F122116112109105101979285
32°F144138134131128124121116110
28°F164157153150146143140135130
24°F185179175170166162158153148
20°F206200195191186182178172164
16°F227220214209204200195190182

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
8,474
Cooling degree days, base 65°F
347
Growing degree days, base 40°F
3,784
Growing degree days, base 45°F
2,799
Growing degree days, base 50°F
1,966
Growing degree days, base 55°F
1,281
Growing degree days, base 60°F
732

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50300
February1,25400
March1,07703
April677024
May3834152
June13331351
July26154593
August49137553
September26820235
October673148
November1,03708
December1,39500

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 13.7 km from Blaine 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 USC00243118 (Ft Belknap 2 Sw). Public domain.