Custer County climate

Custer County Frost Dates and Growing Season

NOAA 1991-2020 normals for Wind Cave, 13.7 km from Custer County, elevation 4155 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wind Cave. 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 15 and the first fall freeze around September 29, a growing season of about 133 days.

Median at 36°F
last May 28, first September 21
Median at 32°F
last May 15, first September 29
Median at 28°F
last May 5, 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 12Jun 6Jun 2May 31May 28May 25May 22May 19May 15
32°FMay 30May 25May 21May 18May 15May 13May 11May 8May 4
28°FMay 18May 13May 10May 7May 5May 3May 1Apr 28Apr 22
24°FMay 7May 3May 1Apr 29Apr 25Apr 22Apr 18Apr 14Apr 9
20°FApr 30Apr 25Apr 20Apr 17Apr 14Apr 11Apr 6Apr 2Mar 29
16°FApr 22Apr 16Apr 11Apr 6Apr 3Mar 31Mar 27Mar 21Mar 14

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 3Sep 10Sep 14Sep 17Sep 21Sep 23Sep 26Sep 29Oct 2
32°FSep 13Sep 20Sep 23Sep 26Sep 29Oct 1Oct 3Oct 6Oct 11
28°FSep 24Sep 28Oct 1Oct 4Oct 6Oct 10Oct 13Oct 17Oct 20
24°FOct 2Oct 7Oct 11Oct 15Oct 17Oct 20Oct 22Oct 25Oct 29
20°FOct 11Oct 16Oct 19Oct 22Oct 25Oct 28Nov 1Nov 5Nov 10
16°FOct 16Oct 22Oct 27Oct 30Nov 3Nov 7Nov 10Nov 14Nov 20

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°F1311251201161121081049890
32°F152145140137133130125119113
28°F171165161157153149145140133
24°F194187182177173169165161154
20°F217208202197193188184179171
16°F237228223217212207202196187

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
6,950
Cooling degree days, base 65°F
482
Growing degree days, base 40°F
4,323
Growing degree days, base 45°F
3,248
Growing degree days, base 50°F
2,340
Growing degree days, base 55°F
1,578
Growing degree days, base 60°F
954

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,17000
February1,03301
March873013
April622144
May3619176
June10365416
July19194640
August29161597
September16551351
October538290
November873010
December1,16500

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 13.7 km from Custer 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 USC00399347 (Wind Cave). Public domain.