Shelley climate

Shelley Frost Dates and Growing Season

NOAA 1991-2020 normals for Idaho Falls Fanning Fld, 15.7 km from Shelley, elevation 4729 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Idaho Falls Fanning Fld. 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 23 and the first fall freeze around September 20, a growing season of about 114 days.

Median at 36°F
last June 14, first September 5
Median at 32°F
last May 23, first September 20
Median at 28°F
last May 7, first October 2

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°FJul 2Jun 26Jun 22Jun 17Jun 14Jun 11Jun 7Jun 4May 28
32°FJun 13Jun 7Jun 2May 28May 23May 19May 15May 11May 7
28°FMay 23May 17May 12May 9May 7May 4May 1Apr 29Apr 23
24°FMay 10May 4Apr 30Apr 27Apr 24Apr 20Apr 15Apr 11Apr 4
20°FApr 29Apr 22Apr 16Apr 11Apr 6Apr 1Mar 28Mar 20Mar 14
16°FApr 9Mar 31Mar 26Mar 21Mar 16Mar 12Mar 9Mar 6Mar 3

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°FAug 20Aug 26Aug 30Sep 2Sep 5Sep 8Sep 11Sep 16Sep 22
32°FSep 1Sep 7Sep 12Sep 17Sep 20Sep 23Sep 27Sep 30Oct 4
28°FSep 15Sep 22Sep 26Sep 29Oct 2Oct 5Oct 8Oct 11Oct 16
24°FSep 28Oct 3Oct 7Oct 11Oct 14Oct 17Oct 20Oct 23Oct 28
20°FOct 10Oct 16Oct 20Oct 23Oct 25Oct 28Oct 31Nov 3Nov 9
16°FOct 20Oct 26Oct 29Nov 1Nov 4Nov 7Nov 11Nov 16Nov 22

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°F1039489847975706456
32°F1391311251201141091039688
28°F167160155151146142138132124
24°F196187181177172168163158151
20°F226220212205201196190184174
16°F255247241236231226221215205

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
7,792
Cooling degree days, base 65°F
249
Growing degree days, base 40°F
3,673
Growing degree days, base 45°F
2,679
Growing degree days, base 50°F
1,843
Growing degree days, base 55°F
1,160
Growing degree days, base 60°F
624

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,38300
February1,12100
March89102
April617023
May3802141
June16224318
July29120556
August4391513
September23112250
October622040
November97701
December1,33800

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 15.7 km from Shelley. 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 USW00024145 (Idaho Falls Fanning Fld). Public domain.