Brawley Frost Dates and Growing Season

NOAA 1991-2020 normals for Brawley 2 Sw, 3.8 km from Brawley, elevation -100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Brawley 2 Sw. 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 16 and the first fall freeze around December 19, a growing season of about 335 days.

Median at 36°F: last February 10, first December 6
Median at 32°F: last January 16, first December 19
Median at 28°F: last January 2, first December 29

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	Feb 28	Feb 24	Feb 19	Feb 14	Feb 10	Feb 4	Jan 31	Jan 22	Jan 13
32°F	Feb 17	Feb 7	Feb 1	Jan 24	Jan 16	Jan 10	Jan 5	Dec 31	Dec 21
28°F	Feb 2	Jan 18	Jan 10	Jan 5	Jan 2	Dec 29	Dec 25	Dec 19	Dec 12
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 22	Nov 27	Dec 1	Dec 4	Dec 6	Dec 9	Dec 13	Dec 16	Dec 21
32°F	Dec 2	Dec 7	Dec 11	Dec 15	Dec 19	Dec 23	Dec 28	Jan 3	Jan 17
28°F	Dec 10	Dec 16	Dec 21	Dec 25	Dec 29	Jan 1	Jan 5	Jan 11	Jan 27
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	328	318	311	305	298	292	286	280	272
32°F	363	354	348	342	335	330	323	315	305
28°F	365	365	365	365	365	365	361	354	345
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: 100% of years
32°F or colder: 91% of years
28°F or colder: 34% of years
24°F or colder: 2% 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: 909
Cooling degree days, base 65°F: 4,154
Growing degree days, base 40°F: 12,371
Growing degree days, base 45°F: 10,547
Growing degree days, base 50°F: 8,739
Growing degree days, base 55°F: 7,017
Growing degree days, base 60°F: 5,478

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	265	3	209
February	160	10	271
March	69	85	481
April	18	191	623
May	2	397	860
June	0	636	1,086
July	0	849	1,314
August	0	871	1,336
September	0	676	1,127
October	3	363	825
November	89	72	435
December	303	1	174

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 3.8 km from Brawley. 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 USC00041048 (Brawley 2 Sw). Public domain.