Hidden Spring climate

Hidden Spring Frost Dates and Growing Season

NOAA 1991-2020 normals for Boise 7 N, 4.3 km from Hidden Spring, elevation 3885 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Boise 7 N. 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 17 and the first fall freeze around October 12, a growing season of about 147 days.

Median at 36°F
last June 6, first September 29
Median at 32°F
last May 17, first October 12
Median at 28°F
last April 27, first October 24

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 23Jun 16Jun 13Jun 9Jun 6Jun 3May 31May 25May 18
32°FJun 10Jun 3May 28May 22May 17May 13May 8May 3Apr 27
28°FMay 19May 11May 5May 1Apr 27Apr 24Apr 20Apr 15Apr 7
24°FApr 29Apr 20Apr 13Apr 9Apr 4Mar 30Mar 25Mar 16Mar 7
20°FApr 2Mar 24Mar 14Mar 9Mar 4Feb 28Feb 24Feb 18Feb 13
16°FMar 7Mar 1Feb 25Feb 20Feb 17Feb 12Feb 6Jan 31Jan 20

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 13Sep 19Sep 24Sep 27Sep 29Oct 2Oct 6Oct 10Oct 16
32°FSep 27Oct 1Oct 5Oct 9Oct 12Oct 15Oct 19Oct 23Oct 30
28°FOct 8Oct 13Oct 18Oct 21Oct 24Oct 28Oct 31Nov 4Nov 11
24°FOct 19Oct 25Oct 30Nov 2Nov 5Nov 9Nov 13Nov 18Nov 24
20°FOct 29Nov 4Nov 9Nov 13Nov 18Nov 22Nov 25Nov 29Dec 4
16°FNov 7Nov 13Nov 20Nov 24Nov 28Dec 1Dec 4Dec 9Dec 17

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°F1401311241191141091049788
32°F172164157152147142136129120
28°F203194189184179172167160152
24°F244234227220212207200193182
20°F282272265259252245238231219
16°F314302295289283276270263253

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
6,167
Cooling degree days, base 65°F
648
Growing degree days, base 40°F
4,654
Growing degree days, base 45°F
3,507
Growing degree days, base 50°F
2,549
Growing degree days, base 55°F
1,766
Growing degree days, base 60°F
1,136

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,07900
February85001
March716013
April546149
May32112197
June13763381
July19257704
August21237682
September13173398
October4555115
November81009
December1,08300

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 4.3 km from Hidden Spring. 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 USC00101017 (Boise 7 N). Public domain.