Plains climate

Plains Frost Dates and Growing Season

NOAA 1991-2020 normals for Superior, 29.7 km from Plains, elevation 2710 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Superior. 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 17 and the first fall freeze around September 23, a growing season of about 125 days.

Median at 36°F
last June 5, first September 9
Median at 32°F
last May 17, first September 23
Median at 28°F
last May 1, first October 6

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

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°F118109103979287797062
32°F15014213613112512011410696
28°F180172166161157152147138128
24°F220210202197191185179171160
20°F255246240234228223215208195
16°F283273266260254248242235224

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
6,694
Cooling degree days, base 65°F
400
Growing degree days, base 40°F
4,098
Growing degree days, base 45°F
3,026
Growing degree days, base 50°F
2,129
Growing degree days, base 55°F
1,393
Growing degree days, base 60°F
815

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12700
February92000
March77504
April557040
May3098193
June14341351
July32173606
August34151583
September19026295
October552056
November90302
December1,15300

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 29.7 km from Plains. 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 USW00024159 (Superior). Public domain.