Idyllwild climate

Idyllwild Frost Dates and Growing Season

NOAA 1991-2020 normals for Idyllwild Fire Dept, 2.2 km from Idyllwild, elevation 5380 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Idyllwild Fire Dept. 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 16 and the first fall freeze around October 24, a growing season of about 160 days.

Median at 36°F
last June 1, first October 6
Median at 32°F
last May 16, first October 24
Median at 28°F
last April 24, first November 10

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 19Jun 11Jun 7Jun 3Jun 1May 30May 26May 21May 14
32°FJun 5May 31May 27May 21May 16May 11May 5Apr 29Apr 23
28°FMay 19May 10May 3Apr 28Apr 24Apr 19Apr 13Apr 7Mar 31
24°FMay 3Apr 21Apr 12Apr 5Mar 31Mar 23Mar 16Mar 7Mar 1
20°FApr 6Mar 20Mar 8Mar 3Feb 25Feb 16Feb 4Jan 22Jan 4
16°FMar 4Feb 25Feb 16Feb 9Feb 1Jan 21Jan 10Jan 3Dec 23

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 17Sep 24Sep 29Oct 2Oct 6Oct 10Oct 14Oct 18Oct 26
32°FOct 1Oct 9Oct 14Oct 19Oct 24Oct 29Nov 1Nov 6Nov 11
28°FOct 17Oct 28Nov 2Nov 6Nov 10Nov 15Nov 19Nov 25Dec 3
24°FNov 9Nov 16Nov 21Nov 26Dec 1Dec 6Dec 10Dec 15Dec 23
20°FNov 24Dec 2Dec 11Dec 16Dec 22Dec 26Jan 1Jan 11Jan 29
16°FDec 11Dec 21Dec 29Jan 2Jan 10Jan 20Jan 31Feb 13Feb 26

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°F153144137132127123117111101
32°F191181174167160153147140131
28°F234224215208200194188179167
24°F285272263254246237229221207
20°F352331317306298287279267249
16°F365365365365354340327311298

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
96% of years
16°F or colder
57% 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
4,321
Cooling degree days, base 65°F
525
Growing degree days, base 40°F
5,549
Growing degree days, base 45°F
4,072
Growing degree days, base 50°F
2,838
Growing degree days, base 55°F
1,858
Growing degree days, base 60°F
1,095

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January681014
February631016
March601032
April464081
May29313221
June9465425
July14177628
August9183639
September6680465
October2627237
November501069
December705012

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 2.2 km from Idyllwild. 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 USC00044211 (Idyllwild Fire Dept). Public domain.