Temecula Frost Dates and Growing Season

NOAA 1991-2020 normals for Fallbrook 5 Ne, 7.2 km from Temecula, elevation 1140 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Fallbrook 5 Ne. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

A freeze (32°F or colder) happens in only 17 percent of years at Fallbrook 5 Ne, so there is no typical freeze season.

Median at 36°F: last February 7, first January 1
Median at 32°F: last February 2, first January 30

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	Mar 6	Feb 28	Feb 22	Feb 16	Feb 7	Jan 27	Jan 14	Jan 3	Dec 21
32°F	Feb 24	Feb 18	Feb 14	Feb 9	Feb 2	Jan 15	Jan 6	Jan 1	Dec 26
28°F	–	–	–	–	–	–	–	–	–
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	Dec 11	Dec 17	Dec 23	Dec 28	Jan 1	Jan 9	Jan 20	Feb 4	Feb 17
32°F	Dec 23	Dec 31	Jan 3	Jan 11	Jan 30	Feb 7	Feb 12	Feb 17	Feb 24
28°F	–	–	–	–	–	–	–	–	–
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	365	365	364	357	346	333	316	307	295
32°F	365	365	365	365	365	365	365	365	356
28°F	365	365	365	365	365	365	365	365	365
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: 73% of years
32°F or colder: 17% of years
28°F or colder: 0% 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: 1,368
Cooling degree days, base 65°F: 1,412
Growing degree days, base 40°F: 9,169
Growing degree days, base 45°F: 7,347
Growing degree days, base 50°F: 5,564
Growing degree days, base 55°F: 3,924
Growing degree days, base 60°F: 2,514

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	248	13	242
February	249	13	200
March	206	20	282
April	145	34	340
May	82	52	436
June	14	115	551
July	1	267	732
August	0	327	792
September	2	295	742
October	25	197	637
November	125	68	395
December	271	11	216

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 7.2 km from Temecula. 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 USW00053151 (Fallbrook 5 Ne). Public domain.