Brule County climate

Brule County Frost Dates and Growing Season

NOAA 1991-2020 normals for Chamberlain 5 S, 18.7 km from Brule County, elevation 1704 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Chamberlain 5 S. 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 3 and the first fall freeze around October 7, a growing season of about 156 days.

Median at 36°F
last May 12, first September 29
Median at 32°F
last May 3, first October 7
Median at 28°F
last April 24, first October 17

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 27May 22May 18May 15May 12May 9May 7May 4May 1
32°FMay 17May 11May 8May 5May 3May 1Apr 29Apr 25Apr 19
28°FMay 6May 2Apr 30Apr 27Apr 24Apr 21Apr 17Apr 14Apr 9
24°FApr 29Apr 24Apr 19Apr 16Apr 13Apr 10Apr 7Apr 4Mar 30
20°FApr 19Apr 13Apr 10Apr 6Apr 4Apr 1Mar 29Mar 24Mar 17
16°FApr 10Apr 4Apr 1Mar 29Mar 26Mar 22Mar 18Mar 13Mar 8

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 17Sep 22Sep 24Sep 27Sep 29Oct 1Oct 3Oct 7Oct 11
32°FSep 25Sep 29Oct 1Oct 4Oct 7Oct 10Oct 13Oct 17Oct 21
28°FOct 1Oct 7Oct 11Oct 14Oct 17Oct 20Oct 22Oct 25Oct 29
24°FOct 11Oct 17Oct 20Oct 23Oct 25Oct 28Nov 1Nov 4Nov 8
20°FOct 20Oct 25Oct 28Nov 1Nov 3Nov 6Nov 9Nov 13Nov 18
16°FOct 29Nov 1Nov 5Nov 8Nov 11Nov 14Nov 18Nov 21Nov 26

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°F155149146142138135131126121
32°F174168163160156152149145137
28°F193187182178174170166161155
24°F214207203198194190185180173
20°F235228222218213209204198191
16°F253245239235230226221215207

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
7,373
Cooling degree days, base 65°F
793
Growing degree days, base 40°F
4,834
Growing degree days, base 45°F
3,779
Growing degree days, base 50°F
2,847
Growing degree days, base 55°F
2,037
Growing degree days, base 60°F
1,351

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,42600
February1,17501
March966015
April597265
May27827251
June53136533
July8294752
August15240690
September13688411
October5057116
November912014
December1,30300

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 18.7 km from Brule 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 USC00391621 (Chamberlain 5 S). Public domain.