Casper climate

Casper Frost Dates and Growing Season

NOAA 1991-2020 normals for Casper Wwtp, 1.8 km from Casper, elevation 5097 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Casper Wwtp. 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 10 and the first fall freeze around September 29, a growing season of about 138 days.

Median at 36°F
last May 23, first September 19
Median at 32°F
last May 10, first September 29
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°FJun 6Jun 2May 29May 25May 23May 20May 18May 15May 11
32°FMay 24May 19May 16May 13May 10May 8May 5May 3Apr 30
28°FMay 14May 9May 6May 3May 1Apr 30Apr 26Apr 23Apr 17
24°FMay 6May 1Apr 27Apr 23Apr 20Apr 17Apr 14Apr 10Apr 3
20°FApr 26Apr 20Apr 16Apr 12Apr 7Apr 4Apr 1Mar 27Mar 20
16°FApr 16Apr 8Apr 3Mar 31Mar 26Mar 22Mar 17Mar 12Mar 6

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 6Sep 11Sep 14Sep 16Sep 19Sep 22Sep 25Sep 28Oct 2
32°FSep 14Sep 19Sep 23Sep 26Sep 29Oct 1Oct 4Oct 7Oct 12
28°FSep 21Sep 27Oct 1Oct 3Oct 6Oct 10Oct 14Oct 17Oct 23
24°FSep 30Oct 5Oct 10Oct 14Oct 17Oct 20Oct 23Oct 26Nov 1
20°FOct 7Oct 14Oct 18Oct 22Oct 25Oct 29Nov 1Nov 5Nov 11
16°FOct 19Oct 24Oct 28Nov 1Nov 4Nov 8Nov 12Nov 16Nov 22

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°F13412812412011611210810396
32°F155149145142138134130125118
28°F178171165160156152148144136
24°F201193187182177172168162153
20°F226216210205199195189182173
16°F247238233227221215210204195

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
6,956
Cooling degree days, base 65°F
564
Growing degree days, base 40°F
4,373
Growing degree days, base 45°F
3,309
Growing degree days, base 50°F
2,405
Growing degree days, base 55°F
1,655
Growing degree days, base 60°F
1,043

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,16700
February1,01901
March873010
April639036
May35812188
June9577434
July9236692
August23201643
September18936316
October562172
November860012
December1,16201

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 1.8 km from Casper. 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 USC00481569 (Casper Wwtp). Public domain.