Summerset climate

Summerset Frost Dates and Growing Season

NOAA 1991-2020 normals for Rapid City 4NW, 9.1 km from Summerset, elevation 3479 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rapid City 4NW. 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 5, a growing season of about 147 days.

Median at 36°F
last May 21, first September 27
Median at 32°F
last May 10, first October 5
Median at 28°F
last April 28, first October 15

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 1May 30May 27May 24May 21May 19May 16May 13May 8
32°FMay 25May 19May 15May 12May 10May 7May 4May 1Apr 27
28°FMay 11May 6May 3May 1Apr 28Apr 25Apr 22Apr 18Apr 13
24°FApr 30Apr 27Apr 23Apr 20Apr 16Apr 13Apr 10Apr 7Apr 2
20°FApr 22Apr 17Apr 14Apr 10Apr 7Apr 4Apr 1Mar 28Mar 20
16°FApr 16Apr 11Apr 7Apr 3Mar 31Mar 26Mar 21Mar 16Mar 10

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 11Sep 16Sep 21Sep 24Sep 27Sep 29Oct 2Oct 5Oct 10
32°FSep 20Sep 26Sep 29Oct 2Oct 5Oct 8Oct 11Oct 15Oct 18
28°FSep 28Oct 4Oct 8Oct 12Oct 15Oct 18Oct 21Oct 24Oct 28
24°FOct 8Oct 14Oct 18Oct 22Oct 24Oct 27Oct 30Nov 1Nov 6
20°FOct 17Oct 22Oct 25Oct 28Nov 1Nov 4Nov 7Nov 10Nov 15
16°FOct 23Oct 28Nov 1Nov 5Nov 8Nov 11Nov 14Nov 18Nov 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°F146139135131127123120115109
32°F166159156151147143139134127
28°F188181176171168163159154146
24°F209202197192188183179174167
20°F228221216211206201197192183
16°F249240232227223217212207197

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
7,285
Cooling degree days, base 65°F
495
Growing degree days, base 40°F
4,257
Growing degree days, base 45°F
3,208
Growing degree days, base 50°F
2,317
Growing degree days, base 55°F
1,569
Growing degree days, base 60°F
959

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,23901
February1,08802
March941011
April669039
May3819166
June10964410
July18201648
August30169605
September18749332
October557289
November888014
December1,17801

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 9.1 km from Summerset. 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 USC00396947 (Rapid City 4NW). Public domain.