Power County climate

Power County Frost Dates and Growing Season

NOAA 1991-2020 normals for American Falls, 12 km from Power County, elevation 4510 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for American Falls. 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 4 and the first fall freeze around October 8, a growing season of about 155 days.

Median at 36°F
last May 20, first September 25
Median at 32°F
last May 4, first October 8
Median at 28°F
last April 19, first October 21

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

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°F147140135130126121115109101
32°F176169163159155151146141134
28°F206199193188185180175170162
24°F238230223217212207202196188
20°F261254248243238233227220212
16°F285276270265261256251245237

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
6,507
Cooling degree days, base 65°F
608
Growing degree days, base 40°F
4,621
Growing degree days, base 45°F
3,504
Growing degree days, base 50°F
2,554
Growing degree days, base 55°F
1,762
Growing degree days, base 60°F
1,114

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19000
February97800
March76109
April525049
May26615235
June9777432
July7267725
August15208659
September14239356
October504288
November85103
December1,17000

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 12 km from Power 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 USC00100218 (American Falls). Public domain.