Cheyenne climate

Cheyenne Frost Dates and Growing Season

NOAA 1991-2020 normals for Cheyenne WFO, 1.7 km from Cheyenne, elevation 6119 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cheyenne WFO. 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 14 and the first fall freeze around October 1, a growing season of about 139 days.

Median at 36°F
last May 26, first September 24
Median at 32°F
last May 14, first October 1
Median at 28°F
last May 3, first October 10

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 7Jun 3May 31May 28May 26May 23May 20May 17May 13
32°FMay 28May 23May 20May 17May 14May 12May 9May 7May 3
28°FMay 17May 12May 8May 6May 3May 1Apr 30Apr 26Apr 20
24°FMay 7May 3Apr 30Apr 27Apr 23Apr 20Apr 17Apr 13Apr 8
20°FApr 30Apr 24Apr 19Apr 16Apr 12Apr 9Apr 4Apr 1Mar 24
16°FApr 21Apr 14Apr 8Apr 3Mar 31Mar 27Mar 22Mar 16Mar 9

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 11Sep 15Sep 19Sep 22Sep 24Sep 26Sep 29Oct 1Oct 5
32°FSep 17Sep 23Sep 26Sep 29Oct 1Oct 3Oct 6Oct 10Oct 14
28°FSep 27Oct 1Oct 4Oct 7Oct 10Oct 13Oct 15Oct 19Oct 23
24°FOct 4Oct 9Oct 13Oct 16Oct 19Oct 22Oct 25Oct 29Nov 3
20°FOct 12Oct 17Oct 21Oct 24Oct 27Oct 31Nov 3Nov 7Nov 13
16°FOct 19Oct 24Oct 28Nov 1Nov 4Nov 8Nov 12Nov 17Nov 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°F136130126123120117112107101
32°F155149145142139134130126119
28°F175170164161157153149145137
24°F199192186180176172169163156
20°F222214207202197192187181174
16°F244234228222217211206200191

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
7,028
Cooling degree days, base 65°F
342
Growing degree days, base 40°F
3,997
Growing degree days, base 45°F
2,944
Growing degree days, base 50°F
2,065
Growing degree days, base 55°F
1,346
Growing degree days, base 60°F
771

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10701
February99501
March87109
April677026
May4104147
June12147380
July19152598
August39112538
September20926290
October585168
November86908
December1,12701

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 1.7 km from Cheyenne. 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 USC00481676 (Cheyenne WFO). Public domain.