Box Elder County climate

Box Elder County Frost Dates and Growing Season

NOAA 1991-2020 normals for Rosette, 43 km from Box Elder County, elevation 5685 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rosette. 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 21 and the first fall freeze around October 2, a growing season of about 132 days.

Median at 36°F
last June 4, first September 24
Median at 32°F
last May 21, first October 2
Median at 28°F
last May 3, first October 12

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 21Jun 15Jun 11Jun 8Jun 4Jun 1May 30May 24May 18
32°FJun 11Jun 4May 31May 26May 21May 17May 12May 8May 2
28°FMay 25May 17May 12May 7May 3Apr 30Apr 27Apr 22Apr 16
24°FMay 10May 1Apr 25Apr 21Apr 18Apr 14Apr 9Apr 3Mar 28
20°FApr 21Apr 14Apr 8Apr 4Mar 31Mar 26Mar 19Mar 15Mar 9
16°FApr 8Mar 30Mar 21Mar 14Mar 10Mar 7Mar 3Feb 28Feb 20

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 8Sep 13Sep 17Sep 20Sep 24Sep 26Sep 28Oct 1Oct 7
32°FSep 17Sep 23Sep 26Sep 29Oct 2Oct 5Oct 8Oct 12Oct 17
28°FSep 27Oct 1Oct 5Oct 8Oct 12Oct 15Oct 19Oct 23Oct 27
24°FOct 5Oct 11Oct 16Oct 20Oct 23Oct 27Oct 30Nov 3Nov 9
20°FOct 16Oct 22Oct 27Oct 31Nov 3Nov 6Nov 10Nov 14Nov 19
16°FOct 26Nov 1Nov 6Nov 10Nov 13Nov 16Nov 20Nov 23Nov 29

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°F1321241181131091041009487
32°F157148142137132126121114104
28°F183175170166161155150144134
24°F215205198193188182177169162
20°F244235228222216210205197187
16°F269262256250244238231224213

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
7,102
Cooling degree days, base 65°F
570
Growing degree days, base 40°F
4,220
Growing degree days, base 45°F
3,205
Growing degree days, base 50°F
2,343
Growing degree days, base 55°F
1,630
Growing degree days, base 60°F
1,040

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,23500
February1,00400
March85403
April632031
May3768160
June14466381
July17243691
August20204649
September16747347
October534279
November90302
December1,21700

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 43 km from Box Elder 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 USC00427408 (Rosette). Public domain.