Stanley County climate

Stanley County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ft Pierre 17 Wsw, 19.6 km from Stanley County, elevation 1590 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ft Pierre 17 Wsw. 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 September 27, a growing season of about 138 days.

Median at 36°F
last May 21, first September 19
Median at 32°F
last May 10, first September 27
Median at 28°F
last May 1, first October 5

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 29May 26May 23May 21May 18May 15May 11May 7
32°FMay 25May 20May 16May 13May 10May 7May 5May 2Apr 29
28°FMay 15May 10May 6May 3May 1Apr 29Apr 26Apr 22Apr 17
24°FMay 6May 2Apr 28Apr 25Apr 22Apr 19Apr 16Apr 12Apr 8
20°FApr 27Apr 22Apr 19Apr 15Apr 12Apr 9Apr 6Apr 2Mar 27
16°FApr 20Apr 15Apr 10Apr 6Apr 3Mar 31Mar 26Mar 20Mar 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 7Sep 11Sep 14Sep 17Sep 19Sep 22Sep 24Sep 27Oct 1
32°FSep 13Sep 18Sep 21Sep 24Sep 27Sep 30Oct 2Oct 5Oct 10
28°FSep 20Sep 26Sep 30Oct 3Oct 5Oct 8Oct 12Oct 16Oct 20
24°FSep 28Oct 3Oct 8Oct 12Oct 15Oct 18Oct 21Oct 24Oct 29
20°FOct 7Oct 14Oct 18Oct 22Oct 24Oct 27Oct 30Nov 2Nov 6
16°FOct 19Oct 24Oct 27Oct 31Nov 2Nov 4Nov 7Nov 10Nov 16

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°F141133129125121117114109103
32°F157150145141138134131125118
28°F176170165160156152147141135
24°F196189183179175171167161153
20°F218209203198194189185180171
16°F236229223218213209204198191

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
7,173
Cooling degree days, base 65°F
894
Growing degree days, base 40°F
5,014
Growing degree days, base 45°F
3,936
Growing degree days, base 50°F
2,991
Growing degree days, base 55°F
2,170
Growing degree days, base 60°F
1,466

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,40400
February1,13901
March901017
April540377
May24635280
June44150557
July4331792
August13277728
September12792424
October5116107
November93507
December1,31000

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 19.6 km from Stanley 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 USC00393076 (Ft Pierre 17 Wsw). Public domain.