Vallejo Frost Dates and Growing Season

NOAA 1991-2020 normals for Vallejo, 6.2 km from Vallejo, elevation 341 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Vallejo. 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 17 and the first fall freeze around December 27, a growing season of about 346 days.

Median at 36°F: last March 4, first December 7
Median at 32°F: last January 17, first December 27
Median at 28°F: last January 5, first January 2

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 8	Mar 29	Mar 20	Mar 13	Mar 4	Feb 27	Feb 15	Feb 1	Jan 19
32°F	Mar 4	Feb 18	Feb 2	Jan 25	Jan 17	Jan 11	Jan 5	Dec 31	Dec 23
28°F	Jan 19	Jan 14	Jan 11	Jan 8	Jan 5	Jan 2	Dec 31	Dec 26	Dec 19
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 21	Nov 27	Dec 1	Dec 3	Dec 7	Dec 11	Dec 14	Dec 21	Jan 2
32°F	Dec 4	Dec 11	Dec 17	Dec 21	Dec 27	Jan 1	Jan 7	Jan 16	Feb 4
28°F	Dec 13	Dec 23	Dec 29	Dec 31	Jan 2	Jan 6	Jan 10	Jan 13	Jan 19
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	311	299	290	279	270	261	253	241
32°F	365	365	359	353	346	338	331	319	291
28°F	365	365	365	365	365	365	365	363	354
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: 75% of years
28°F or colder: 23% of years
24°F or colder: 4% 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: 2,093
Cooling degree days, base 65°F: 868
Growing degree days, base 40°F: 7,902
Growing degree days, base 45°F: 6,095
Growing degree days, base 50°F: 4,389
Growing degree days, base 55°F: 2,936
Growing degree days, base 60°F: 1,768

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	476	0	44
February	309	2	130
March	248	5	226
April	168	16	299
May	66	55	454
June	18	126	558
July	4	176	637
August	2	190	653
September	7	196	639
October	54	94	505
November	270	8	198
December	471	0	46

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 6.2 km from Vallejo. 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 USC00049219 (Vallejo). Public domain.