Twin Falls climate

Twin Falls Frost Dates and Growing Season

NOAA 1991-2020 normals for Twin Falls-Kmvt, 2 km from Twin Falls, elevation 3670 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Twin Falls-Kmvt. 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 April 30 and the first fall freeze around October 9, a growing season of about 161 days.

Median at 36°F
last May 14, first September 28
Median at 32°F
last April 30, first October 9
Median at 28°F
last April 17, first October 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°FJun 2May 27May 20May 16May 14May 10May 7May 4May 1
32°FMay 14May 8May 4May 2Apr 30Apr 28Apr 25Apr 21Apr 17
28°FApr 30Apr 27Apr 23Apr 20Apr 17Apr 13Apr 9Apr 5Mar 30
24°FApr 17Apr 11Apr 6Apr 1Mar 28Mar 22Mar 14Mar 10Mar 4
20°FMar 30Mar 16Mar 10Mar 6Mar 4Mar 1Feb 26Feb 20Feb 15
16°FMar 7Mar 3Feb 28Feb 25Feb 21Feb 17Feb 13Feb 7Jan 31

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 12Sep 17Sep 22Sep 25Sep 28Oct 1Oct 3Oct 6Oct 12
32°FSep 24Oct 1Oct 3Oct 6Oct 9Oct 13Oct 16Oct 19Oct 24
28°FOct 7Oct 13Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 5
24°FOct 19Oct 25Oct 29Nov 1Nov 3Nov 6Nov 10Nov 13Nov 19
20°FOct 29Nov 2Nov 6Nov 10Nov 14Nov 17Nov 21Nov 24Nov 28
16°FNov 3Nov 10Nov 15Nov 20Nov 23Nov 26Nov 29Dec 4Dec 13

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°F156150145140136132127121112
32°F181173169165161158153149140
28°F211203196191187183179174166
24°F248239232226220214208202193
20°F277267261255250246240234224
16°F303292285280275269264257248

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
5,655
Cooling degree days, base 65°F
795
Growing degree days, base 40°F
5,163
Growing degree days, base 45°F
3,947
Growing degree days, base 50°F
2,921
Growing degree days, base 55°F
2,065
Growing degree days, base 60°F
1,357

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,04200
February83601
March654021
April476277
May22632286
June69110491
July7322781
August13261713
September10564413
October4084129
November76908
December1,05100

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 2 km from Twin 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 USC00109293 (Twin Falls-Kmvt). Public domain.