Jerome County climate

Jerome County Frost Dates and Growing Season

NOAA 1991-2020 normals for Twin Falls 6 E, 17.4 km from Jerome County, elevation 3960 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Twin Falls 6 E. 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 6 and the first fall freeze around October 3, a growing season of about 150 days.

Median at 36°F
last May 23, first September 19
Median at 32°F
last May 6, first October 3
Median at 28°F
last April 20, first October 17

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

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°F13813212712311811210710193
32°F170164159155150146141135126
28°F203194187182177173168162155
24°F240230223217211205199191181
20°F273265259252246241234227215
16°F302292284279273268263256245

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
6,318
Cooling degree days, base 65°F
462
Growing degree days, base 40°F
4,385
Growing degree days, base 45°F
3,255
Growing degree days, base 50°F
2,311
Growing degree days, base 55°F
1,541
Growing degree days, base 60°F
923

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10500
February88201
March724012
April542154
May31010201
June12161393
July19198645
August29159595
September17133323
October494183
November81506
December1,10800

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 17.4 km from Jerome County. 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 USC00109303 (Twin Falls 6 E). Public domain.