Valle Vista Frost Dates and Growing Season

NOAA 1991-2020 normals for Hemet, 1.1 km from Valle Vista, elevation 1811 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hemet. 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 January 10 and the first fall freeze around December 23, a growing season of about 350 days.

Median at 36°F: last February 21, first December 9
Median at 32°F: last January 10, first December 23
Median at 28°F: last December 27, first December 25

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Apr 6	Mar 25	Mar 12	Mar 1	Feb 21	Feb 10	Jan 29	Jan 16	Jan 5
32°F	Feb 25	Feb 13	Jan 31	Jan 19	Jan 10	Jan 3	Dec 30	Dec 24	Dec 14
28°F	Jan 30	Jan 8	Dec 31	Dec 29	Dec 27	Dec 23	Dec 19	Dec 11	Dec 3
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Nov 14	Nov 22	Nov 28	Dec 4	Dec 9	Dec 13	Dec 17	Dec 24	Jan 5
32°F	Nov 27	Dec 5	Dec 11	Dec 17	Dec 23	Dec 27	Jan 1	Jan 12	Jan 31
28°F	Dec 3	Dec 9	Dec 16	Dec 22	Dec 25	Dec 28	Dec 30	Jan 4	Jan 16
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
16°F	–	–	–	–	–	–	–	–	–

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	342	325	314	301	290	279	269	256	237
32°F	365	365	365	358	350	343	333	323	306
28°F	365	365	365	365	365	365	365	365	356
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder: 98% of years
32°F or colder: 67% of years
28°F or colder: 17% of years
24°F or colder: 0% of years
20°F or colder: 0% of years
16°F or colder: 0% 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: 1,516
Cooling degree days, base 65°F: 2,009
Growing degree days, base 40°F: 9,619
Growing degree days, base 45°F: 7,803
Growing degree days, base 50°F: 6,049
Growing degree days, base 55°F: 4,451
Growing degree days, base 60°F: 3,093

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	306	4	185
February	257	12	190
March	209	23	287
April	130	53	376
May	53	134	546
June	8	234	677
July	0	470	935
August	0	501	966
September	4	368	814
October	43	162	585
November	167	45	333
December	340	4	158

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 1.1 km from Valle Vista. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00043896 (Hemet). Public domain.