Bonneville County climate

Bonneville County Frost Dates and Growing Season

NOAA 1991-2020 normals for Idaho Falls 16 Se, 14.5 km from Bonneville County, elevation 5828 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Idaho Falls 16 Se. 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 June 9 and the first fall freeze around September 11, a growing season of about 93 days.

Median at 32°F
last June 9, first September 11
Median at 28°F
last May 19, first September 23

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°F–––––––––
32°FJun 26Jun 21Jun 16Jun 13Jun 9Jun 6Jun 1May 27May 19
28°FJun 10Jun 4May 30May 24May 19May 16May 12May 9May 4
24°FMay 22May 15May 11May 8May 5May 2Apr 30Apr 25Apr 20
20°FMay 8May 2Apr 28Apr 24Apr 20Apr 17Apr 13Apr 8Apr 3
16°FApr 26Apr 19Apr 14Apr 10Apr 6Apr 3Mar 30Mar 24Mar 16

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°F–––––––––
32°FAug 27Sep 1Sep 4Sep 8Sep 11Sep 14Sep 18Sep 22Sep 27
28°FSep 4Sep 11Sep 15Sep 19Sep 23Sep 26Sep 29Oct 4Oct 10
24°FSep 14Sep 21Sep 26Sep 29Oct 2Oct 6Oct 10Oct 15Oct 20
20°FSep 25Oct 1Oct 5Oct 9Oct 13Oct 17Oct 21Oct 25Oct 31
16°FOct 4Oct 11Oct 16Oct 20Oct 24Oct 28Nov 1Nov 5Nov 11

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°F867974696460544839
32°F117110102989388847769
28°F14713813212612111611110496
24°F171164158154149144138131122
20°F200191185179174169163156147
16°F228218211205199194189182173

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
8,450
Cooling degree days, base 65°F
136
Growing degree days, base 40°F
3,069
Growing degree days, base 45°F
2,168
Growing degree days, base 50°F
1,430
Growing degree days, base 55°F
843
Growing degree days, base 60°F
408

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,32400
February1,13300
March99400
April744010
May489183
June25610225
July6874472
August9247422
September3095187
October685030
November1,01701
December1,34100

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 14.5 km from Bonneville 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 USC00104456 (Idaho Falls 16 Se). Public domain.