Morton County climate

Morton County Frost Dates and Growing Season

NOAA 1991-2020 normals for New Salem 5NW, 25.2 km from Morton County, elevation 2150 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for New Salem 5NW. 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 18 and the first fall freeze around September 24, a growing season of about 127 days.

Median at 36°F
last May 30, first September 15
Median at 32°F
last May 18, first September 24
Median at 28°F
last May 8, first October 3

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

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 10Sep 12Sep 15Sep 17Sep 20Sep 23Sep 27
32°FSep 12Sep 17Sep 20Sep 22Sep 24Sep 27Sep 30Oct 2Oct 6
28°FSep 21Sep 24Sep 27Oct 1Oct 3Oct 5Oct 8Oct 11Oct 16
24°FSep 28Oct 2Oct 5Oct 8Oct 11Oct 14Oct 16Oct 20Oct 25
20°FOct 5Oct 11Oct 14Oct 17Oct 20Oct 23Oct 26Oct 30Nov 3
16°FOct 13Oct 18Oct 22Oct 26Oct 29Nov 1Nov 4Nov 7Nov 12

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°F125119115111106103999487
32°F146139134131127123119114107
28°F166160155151147143139134129
24°F185179174170165162158153147
20°F203197192187184180175171163
16°F221213208204200196191186179

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
8,946
Cooling degree days, base 65°F
418
Growing degree days, base 40°F
3,867
Growing degree days, base 45°F
2,932
Growing degree days, base 50°F
2,111
Growing degree days, base 55°F
1,413
Growing degree days, base 60°F
843

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,65800
February1,37200
March1,14403
April712134
May37110177
June11757394
July32164597
August49147563
September23038285
October665255
November1,09203
December1,50300

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 25.2 km from Morton 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 USC00326365 (New Salem 5NW). Public domain.