Thermopolis climate

Thermopolis Frost Dates and Growing Season

NOAA 1991-2020 normals for Thermopolis, 0.7 km from Thermopolis, elevation 4321 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Thermopolis. 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 5 and the first fall freeze around October 5, a growing season of about 152 days.

Median at 36°F
last May 19, first September 25
Median at 32°F
last May 5, first October 5
Median at 28°F
last April 23, first October 15

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

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 13Sep 17Sep 20Sep 23Sep 25Sep 28Sep 30Oct 3Oct 7
32°FSep 23Sep 27Sep 30Oct 2Oct 5Oct 7Oct 10Oct 14Oct 18
28°FOct 1Oct 5Oct 9Oct 13Oct 15Oct 18Oct 20Oct 23Oct 27
24°FOct 11Oct 15Oct 19Oct 22Oct 24Oct 27Oct 30Nov 2Nov 6
20°FOct 18Oct 23Oct 26Oct 30Nov 1Nov 4Nov 7Nov 10Nov 15
16°FOct 24Oct 30Nov 3Nov 6Nov 8Nov 11Nov 14Nov 18Nov 23

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°F145139135131127124120116111
32°F168163159155152148145140134
28°F194187182178173169165160153
24°F217210205200197192188183175
20°F241233227222216211206201192
16°F257250244239234228222215207

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
6,690
Cooling degree days, base 65°F
737
Growing degree days, base 40°F
4,866
Growing degree days, base 45°F
3,748
Growing degree days, base 50°F
2,780
Growing degree days, base 55°F
1,961
Growing degree days, base 60°F
1,283

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,25900
February1,01901
March781015
April521166
May26818245
June62115504
July5298758
August13242694
September13061390
October4943101
November89607
December1,24300

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 0.7 km from Thermopolis. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00488875 (Thermopolis). Public domain.