Cheyenne County climate

Cheyenne County Frost Dates and Growing Season

NOAA 1991-2020 normals for Saint Francis, 6.8 km from Cheyenne County, elevation 3336 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Saint Francis. 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 30 and the first fall freeze around October 10, a growing season of about 160 days.

Median at 36°F
last May 10, first October 3
Median at 32°F
last April 30, first October 10
Median at 28°F
last April 20, first October 18

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 25May 19May 16May 13May 10May 8May 5May 2Apr 28
32°FMay 15May 10May 6May 3Apr 30Apr 28Apr 25Apr 21Apr 18
28°FMay 4Apr 30Apr 26Apr 23Apr 20Apr 18Apr 15Apr 12Apr 6
24°FApr 23Apr 19Apr 15Apr 12Apr 8Apr 5Apr 2Mar 30Mar 23
20°FApr 13Apr 7Apr 3Mar 31Mar 27Mar 23Mar 19Mar 14Mar 8
16°FApr 4Mar 31Mar 25Mar 21Mar 15Mar 11Mar 8Mar 4Feb 28

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 20Sep 25Sep 28Oct 1Oct 3Oct 5Oct 7Oct 9Oct 12
32°FSep 27Oct 3Oct 6Oct 8Oct 10Oct 12Oct 15Oct 17Oct 20
28°FOct 5Oct 10Oct 13Oct 16Oct 18Oct 20Oct 23Oct 25Oct 28
24°FOct 14Oct 19Oct 22Oct 24Oct 27Oct 29Oct 31Nov 3Nov 8
20°FOct 21Oct 26Oct 30Nov 1Nov 4Nov 7Nov 10Nov 15Nov 20
16°FOct 27Nov 1Nov 5Nov 10Nov 13Nov 17Nov 21Nov 25Nov 30

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°F159154149146143140136131124
32°F178172168164160157153149143
28°F196190186182178175171166159
24°F220214209204200196191186180
20°F243236231226222216211206196
16°F265258251245240236231223215

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
5,817
Cooling degree days, base 65°F
1,097
Growing degree days, base 40°F
5,640
Growing degree days, base 45°F
4,447
Growing degree days, base 50°F
3,401
Growing degree days, base 55°F
2,495
Growing degree days, base 60°F
1,731

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10501
February92803
March732035
April4632109
May20651333
June26226650
July3379841
August7311769
September93120483
October4148156
November767022
December1,07401

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 6.8 km from Cheyenne 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 USC00147093 (Saint Francis). Public domain.