Custer County climate

Custer County Frost Dates and Growing Season

NOAA 1991-2020 normals for Broken Bow 2 W, 4.5 km from Custer County, elevation 2504 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Broken Bow 2 W. 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 10 and the first fall freeze around October 1, a growing season of about 142 days.

Median at 36°F
last May 20, first September 23
Median at 32°F
last May 10, first October 1
Median at 28°F
last May 2, first October 9

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 28May 25May 23May 20May 18May 14May 11May 8
32°FMay 24May 20May 16May 13May 10May 7May 5May 2Apr 28
28°FMay 15May 10May 6May 4May 2Apr 30Apr 26Apr 21Apr 17
24°FMay 6May 1Apr 28Apr 25Apr 21Apr 18Apr 14Apr 10Apr 5
20°FApr 25Apr 20Apr 16Apr 13Apr 9Apr 6Apr 4Mar 31Mar 25
16°FApr 16Apr 10Apr 6Apr 4Mar 31Mar 28Mar 23Mar 19Mar 13

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

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°F143137133130126123119114108
32°F159154149145142138135130125
28°F178172167164160156152147140
24°F199191187183178175170166158
20°F219212207203199195189184177
16°F240233227222218213209203195

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
6,869
Cooling degree days, base 65°F
716
Growing degree days, base 40°F
4,779
Growing degree days, base 45°F
3,691
Growing degree days, base 50°F
2,745
Growing degree days, base 55°F
1,935
Growing degree days, base 60°F
1,260

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,26500
February1,06102
March871018
April571267
May28327248
June55139535
July9260716
August20207653
September15476384
October5045110
November875014
December1,20300

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 4.5 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 USC00251200 (Broken Bow 2 W). Public domain.