Rapid Valley climate

Rapid Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Rapid City WFO, 5.3 km from Rapid Valley, elevation 3379 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rapid City WFO. 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 8, a growing season of about 157 days.

Median at 36°F
last May 15, first October 1
Median at 32°F
last May 3, first October 8
Median at 28°F
last April 22, first October 18

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 29May 24May 21May 18May 15May 11May 9May 5May 1
32°FMay 17May 13May 9May 6May 3May 1Apr 29Apr 25Apr 20
28°FMay 5May 1Apr 28Apr 25Apr 22Apr 19Apr 16Apr 13Apr 8
24°FApr 25Apr 21Apr 18Apr 15Apr 12Apr 9Apr 6Apr 2Mar 27
20°FApr 18Apr 13Apr 9Apr 6Apr 2Mar 31Mar 28Mar 22Mar 14
16°FApr 12Apr 5Apr 1Mar 30Mar 25Mar 21Mar 15Mar 10Mar 3

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 19Sep 23Sep 26Sep 28Oct 1Oct 2Oct 5Oct 8Oct 14
32°FSep 26Sep 29Oct 1Oct 5Oct 8Oct 11Oct 15Oct 18Oct 23
28°FOct 3Oct 9Oct 12Oct 15Oct 18Oct 21Oct 24Oct 27Nov 1
24°FOct 12Oct 17Oct 20Oct 23Oct 27Oct 29Nov 1Nov 5Nov 11
20°FOct 19Oct 25Oct 28Nov 1Nov 3Nov 7Nov 10Nov 14Nov 19
16°FOct 27Oct 31Nov 3Nov 8Nov 11Nov 14Nov 17Nov 22Nov 28

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°F156149145141137133129125118
32°F176170165161157153149145137
28°F200192187183178175170164157
24°F218210205201197192188184177
20°F237228223217213208204199191
16°F256247240235229224218212204

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
6,845
Cooling degree days, base 65°F
680
Growing degree days, base 40°F
4,720
Growing degree days, base 45°F
3,611
Growing degree days, base 50°F
2,664
Growing degree days, base 55°F
1,864
Growing degree days, base 60°F
1,201

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19802
February1,03905
March884022
April616155
May32716207
June8496465
July10257713
August18224671
September15779389
October5226111
November846023
December1,14402

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 5.3 km from Rapid Valley. 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 USC00396948 (Rapid City WFO). Public domain.