Cheyenne County climate

Cheyenne County Frost Dates and Growing Season

NOAA 1991-2020 normals for Sidney 6 Nnw, 2.4 km from Cheyenne County, elevation 4320 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sidney 6 Nnw. 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 8 and the first fall freeze around October 4, a growing season of about 149 days.

Median at 36°F
last May 18, first September 26
Median at 32°F
last May 8, first October 4
Median at 28°F
last April 27, first October 14

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 31May 27May 24May 20May 18May 15May 13May 10May 7
32°FMay 20May 15May 13May 10May 8May 6May 3Apr 30Apr 26
28°FMay 10May 5May 2Apr 30Apr 27Apr 24Apr 21Apr 17Apr 12
24°FMay 1Apr 27Apr 23Apr 20Apr 17Apr 14Apr 10Apr 6Apr 1
20°FApr 24Apr 19Apr 14Apr 10Apr 6Apr 3Mar 30Mar 25Mar 18
16°FApr 16Apr 8Apr 3Mar 30Mar 25Mar 19Mar 14Mar 9Mar 3

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 12Sep 17Sep 21Sep 24Sep 26Sep 29Oct 1Oct 4Oct 7
32°FSep 21Sep 26Sep 29Oct 1Oct 4Oct 7Oct 10Oct 13Oct 17
28°FSep 30Oct 5Oct 8Oct 11Oct 14Oct 16Oct 19Oct 21Oct 26
24°FOct 8Oct 13Oct 16Oct 19Oct 21Oct 24Oct 27Oct 30Nov 4
20°FOct 15Oct 20Oct 23Oct 27Oct 30Nov 2Nov 5Nov 9Nov 15
16°FOct 22Oct 28Nov 1Nov 4Nov 8Nov 12Nov 16Nov 19Nov 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°F146141136133129125122117111
32°F166160156152149145141136131
28°F186180175171167164160156150
24°F208201195190186182178173167
20°F230221216211206201197191182
16°F255245239233228221215207199

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
6,373
Cooling degree days, base 65°F
735
Growing degree days, base 40°F
4,904
Growing degree days, base 45°F
3,770
Growing degree days, base 50°F
2,796
Growing degree days, base 55°F
1,971
Growing degree days, base 60°F
1,285

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12202
February96003
March795022
April564166
May29620233
June61126516
July7282741
August18223670
September13578406
October4905117
November818018
December1,10702

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 2.4 km from Cheyenne County. 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 USC00257830 (Sidney 6 Nnw). Public domain.