Chualar Frost Dates and Growing Season

NOAA 1991-2020 normals for Salinas #2, 16.4 km from Chualar, elevation 45 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Salinas #2. 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 February 4 and the first fall freeze around December 6, a growing season of about 311 days.

Median at 36°F: last March 25, first November 19
Median at 32°F: last February 4, first December 6
Median at 28°F: last December 31, first December 19

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 18	Apr 10	Apr 4	Mar 31	Mar 25	Mar 17	Mar 10	Feb 28	Feb 18
32°F	Mar 11	Feb 28	Feb 21	Feb 12	Feb 4	Jan 27	Jan 15	Jan 4	Dec 25
28°F	Jan 28	Jan 14	Jan 9	Jan 3	Dec 31	Dec 27	Dec 20	Dec 13	Dec 5
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 3	Nov 8	Nov 11	Nov 15	Nov 19	Nov 23	Nov 26	Dec 1	Dec 7
32°F	Nov 18	Nov 24	Nov 30	Dec 2	Dec 6	Dec 10	Dec 16	Dec 25	Jan 5
28°F	Dec 1	Dec 4	Dec 9	Dec 14	Dec 19	Dec 27	Jan 1	Jan 6	Jan 14
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	279	266	256	246	238	231	224	217	208
32°F	348	337	328	320	311	303	292	279	268
28°F	365	365	365	365	364	358	351	342	334
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: 96% of years
28°F or colder: 50% of years
24°F or colder: 3% 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: 2,724
Cooling degree days, base 65°F: 105
Growing degree days, base 40°F: 6,506
Growing degree days, base 45°F: 4,694
Growing degree days, base 50°F: 2,973
Growing degree days, base 55°F: 1,516
Growing degree days, base 60°F: 516

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	394	0	104
February	332	0	109
March	313	1	164
April	270	4	188
May	209	6	262
June	136	7	321
July	91	11	384
August	70	19	414
September	70	28	408
October	134	25	356
November	282	4	182
December	425	0	80

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 16.4 km from Chualar. 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 USC00047668 (Salinas #2). Public domain.