Morton County climate

Morton County Frost Dates and Growing Season

NOAA 1991-2020 normals for Richfield, 8.1 km from Morton County, elevation 3408 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Richfield. 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 April 27 and the first fall freeze around October 19, a growing season of about 173 days.

Median at 36°F
last May 4, first October 8
Median at 32°F
last April 27, first October 19
Median at 28°F
last April 16, first October 26

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 17May 13May 10May 7May 4May 2Apr 30Apr 28Apr 24
32°FMay 9May 5May 1Apr 30Apr 27Apr 24Apr 21Apr 17Apr 11
28°FMay 1Apr 27Apr 23Apr 19Apr 16Apr 13Apr 9Apr 6Apr 1
24°FApr 22Apr 16Apr 12Apr 9Apr 6Apr 4Apr 1Mar 28Mar 21
20°FApr 12Apr 6Apr 3Mar 31Mar 27Mar 23Mar 17Mar 13Mar 7
16°FApr 2Mar 28Mar 22Mar 17Mar 13Mar 9Mar 5Mar 1Feb 22

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 27Oct 1Oct 3Oct 5Oct 8Oct 11Oct 14Oct 17Oct 21
32°FOct 5Oct 9Oct 13Oct 16Oct 19Oct 21Oct 23Oct 26Oct 30
28°FOct 15Oct 19Oct 21Oct 24Oct 26Oct 29Nov 1Nov 3Nov 8
24°FOct 22Oct 27Oct 30Nov 1Nov 3Nov 6Nov 9Nov 13Nov 18
20°FOct 29Nov 3Nov 6Nov 10Nov 13Nov 16Nov 19Nov 23Nov 29
16°FNov 5Nov 11Nov 15Nov 19Nov 22Nov 26Nov 30Dec 4Dec 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°F172167163159155152149144138
32°F191185181177173170166162155
28°F211204200196193189184178172
24°F231224219215211207203198191
20°F255248241236231226221216207
16°F279270263258253247242235227

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
4,814
Cooling degree days, base 65°F
1,393
Growing degree days, base 40°F
6,489
Growing degree days, base 45°F
5,170
Growing degree days, base 50°F
4,010
Growing degree days, base 55°F
3,003
Growing degree days, base 60°F
2,133

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January96903
February780011
March637055
April3659171
May12685434
June11293732
July1441905
August3364826
September51174576
October29826246
November634147
December93905

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 8.1 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 USC00146808 (Richfield). Public domain.