American Falls climate

American Falls Frost Dates and Growing Season

NOAA 1991-2020 normals for American Falls 6 Ne, 8.2 km from American Falls, elevation 4415 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for American Falls 6 Ne. 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 14 and the first fall freeze around October 2, a growing season of about 138 days.

Median at 36°F
last June 5, first September 20
Median at 32°F
last May 14, first October 2
Median at 28°F
last April 29, first October 16

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 12Jun 8Jun 5Jun 2May 29May 23May 17
32°FJun 4May 28May 21May 17May 14May 10May 7May 4Apr 30
28°FMay 14May 8May 5May 2Apr 29Apr 26Apr 23Apr 19Apr 12
24°FMay 1Apr 25Apr 20Apr 16Apr 11Apr 7Apr 4Mar 31Mar 21
20°FApr 13Apr 5Apr 1Mar 29Mar 23Mar 17Mar 13Mar 9Mar 3
16°FMar 27Mar 17Mar 12Mar 9Mar 6Mar 4Mar 1Feb 26Feb 18

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 2Sep 8Sep 12Sep 16Sep 20Sep 23Sep 25Sep 28Oct 3
32°FSep 16Sep 22Sep 26Sep 29Oct 2Oct 5Oct 8Oct 13Oct 17
28°FSep 29Oct 4Oct 8Oct 13Oct 16Oct 19Oct 23Oct 28Nov 2
24°FOct 14Oct 19Oct 24Oct 27Oct 30Nov 2Nov 5Nov 8Nov 13
20°FOct 24Oct 30Nov 1Nov 5Nov 8Nov 11Nov 15Nov 19Nov 25
16°FOct 29Nov 3Nov 9Nov 13Nov 16Nov 20Nov 23Nov 26Dec 1

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°F12712111410910498938880
32°F161153148143138132128121112
28°F191183177173168163158151142
24°F221214208203198193189183175
20°F253245239234228223216209200
16°F277269264258254248243237230

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
6,997
Cooling degree days, base 65°F
363
Growing degree days, base 40°F
4,104
Growing degree days, base 45°F
3,033
Growing degree days, base 50°F
2,129
Growing degree days, base 55°F
1,383
Growing degree days, base 60°F
791

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,25200
February1,01800
March80905
April558142
May3295181
June14035349
July23147589
August27150589
September18325303
October532068
November89604
December1,23100

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 8.2 km from American Falls. 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 USC00100227 (American Falls 6 Ne). Public domain.