Box Elder climate

Box Elder Frost Dates and Growing Season

NOAA 1991-2020 normals for Rapid City Rgnl AP, 7.8 km from Box Elder, elevation 3160 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rapid City Rgnl AP. 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 12 and the first fall freeze around October 1, a growing season of about 139 days.

Median at 36°F
last May 22, first September 21
Median at 32°F
last May 12, 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°FJun 6Jun 1May 28May 25May 22May 20May 17May 14May 10
32°FMay 26May 21May 18May 14May 12May 9May 7May 4May 1
28°FMay 14May 10May 6May 4May 2Apr 30Apr 28Apr 24Apr 18
24°FMay 3Apr 30Apr 27Apr 24Apr 20Apr 17Apr 14Apr 10Apr 5
20°FApr 25Apr 20Apr 17Apr 13Apr 9Apr 6Apr 3Mar 30Mar 23
16°FApr 16Apr 9Apr 6Apr 3Mar 31Mar 27Mar 22Mar 17Mar 11

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 13Sep 16Sep 18Sep 21Sep 23Sep 26Sep 30Oct 3
32°FSep 16Sep 21Sep 25Sep 28Oct 1Oct 3Oct 5Oct 9Oct 14
28°FSep 26Sep 30Oct 3Oct 6Oct 9Oct 13Oct 16Oct 19Oct 23
24°FOct 3Oct 9Oct 14Oct 17Oct 19Oct 22Oct 25Oct 28Nov 1
20°FOct 12Oct 17Oct 20Oct 24Oct 26Oct 29Nov 1Nov 4Nov 9
16°FOct 18Oct 24Oct 28Oct 31Nov 3Nov 6Nov 10Nov 13Nov 18

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°F137132128124121117113109101
32°F157151147143139136131126120
28°F178172167163159155151146137
24°F200194189184180176172166157
20°F219212207203198193189183175
16°F239230225220215211206200192

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
7,252
Cooling degree days, base 65°F
607
Growing degree days, base 40°F
4,440
Growing degree days, base 45°F
3,382
Growing degree days, base 50°F
2,482
Growing degree days, base 55°F
1,722
Growing degree days, base 60°F
1,095

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,26000
February1,09102
March918013
April634145
May34911185
June9381441
July13244696
August25205645
September17562355
October560389
November912011
December1,22300

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 7.8 km from Box Elder. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00024090 (Rapid City Rgnl AP). Public domain.