Custer County climate

Custer County Frost Dates and Growing Season

NOAA 1991-2020 normals for Mizpah 4 Nnw, 21.8 km from Custer County, elevation 2480 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mizpah 4 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 22 and the first fall freeze around September 15, a growing season of about 117 days.

Median at 36°F
last June 2, first September 6
Median at 32°F
last May 22, first September 15
Median at 28°F
last May 11, first September 25

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 22Jun 15Jun 8Jun 5Jun 2May 30May 27May 23May 18
32°FJun 7Jun 1May 29May 25May 22May 19May 16May 12May 9
28°FMay 28May 22May 18May 15May 11May 8May 5May 2Apr 28
24°FMay 16May 10May 5May 2Apr 29Apr 27Apr 23Apr 19Apr 12
20°FMay 5Apr 29Apr 25Apr 22Apr 18Apr 14Apr 10Apr 6Mar 30
16°FApr 25Apr 18Apr 13Apr 9Apr 6Apr 3Mar 31Mar 25Mar 16

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°FAug 22Aug 28Sep 1Sep 3Sep 6Sep 9Sep 12Sep 16Sep 21
32°FSep 2Sep 5Sep 10Sep 13Sep 15Sep 19Sep 22Sep 27Oct 1
28°FSep 10Sep 16Sep 19Sep 22Sep 25Sep 28Oct 1Oct 4Oct 8
24°FSep 18Sep 23Sep 27Sep 30Oct 3Oct 6Oct 9Oct 12Oct 17
20°FSep 26Oct 2Oct 6Oct 9Oct 13Oct 17Oct 20Oct 24Oct 29
16°FOct 7Oct 15Oct 18Oct 22Oct 25Oct 28Oct 31Nov 4Nov 9

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°F116109103999590867971
32°F13713012512111711210810192
28°F157150145141137133128123114
24°F181172167162158153149144136
20°F204195189184180175170163155
16°F227218212207202197193186177

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
7,541
Cooling degree days, base 65°F
682
Growing degree days, base 40°F
4,515
Growing degree days, base 45°F
3,468
Growing degree days, base 50°F
2,567
Growing degree days, base 55°F
1,805
Growing degree days, base 60°F
1,176

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,41200
February1,15500
March91908
April568154
May29915218
June7997470
July11273727
August24239681
September17656344
October583263
November97903
December1,33600

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 21.8 km from Custer 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 USC00245754 (Mizpah 4 Nnw). Public domain.