Vacaville climate

Vacaville Frost Dates and Growing Season

NOAA 1991-2020 normals for Vacaville, 4.9 km from Vacaville, elevation 110 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Vacaville. 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 31 and the first fall freeze around December 11, a growing season of about 318 days.

Median at 36°F
last March 8, first November 26
Median at 32°F
last January 31, first December 11
Median at 28°F
last January 6, first December 23

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.

Threshold10%20%30%40%50%60%70%80%90%
36°FApr 7Mar 29Mar 21Mar 14Mar 8Mar 2Feb 26Feb 19Feb 4
32°FMar 11Feb 25Feb 15Feb 6Jan 31Jan 24Jan 17Jan 7Dec 30
28°FJan 31Jan 23Jan 17Jan 11Jan 6Jan 2Dec 30Dec 23Dec 16
24°FJan 16Jan 9Jan 3Dec 31Dec 30Dec 27Dec 25Dec 20Dec 11
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.

Threshold10%20%30%40%50%60%70%80%90%
36°FNov 10Nov 15Nov 19Nov 22Nov 26Nov 30Dec 2Dec 6Dec 13
32°FNov 24Dec 1Dec 3Dec 7Dec 11Dec 15Dec 21Jan 1Jan 12
28°FDec 4Dec 10Dec 14Dec 19Dec 23Dec 29Jan 3Jan 7Jan 19
24°FDec 9Dec 15Dec 21Dec 26Dec 28Dec 30Jan 3Jan 7Jan 15
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.

Threshold10%20%30%40%50%60%70%80%90%
36°F298283275266259251245235226
32°F355342334327318310301291275
28°F365365365365361354348341334
24°F365365365365365365365365363
20°F365365365365365365365365365
16°F365365365365365365365365365

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
95% of years
28°F or colder
54% of years
24°F or colder
15% of years
20°F or colder
2% 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
2,149
Cooling degree days, base 65°F
1,677
Growing degree days, base 40°F
8,658
Growing degree days, base 45°F
6,871
Growing degree days, base 50°F
5,214
Growing degree days, base 55°F
3,792
Growing degree days, base 60°F
2,623

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January508040
February347097
March2656216
April14033344
May45133553
June4280726
July0426891
August0403868
September2293741
October53100512
November2803185
December505042

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 4.9 km from Vacaville. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00049200 (Vacaville). Public domain.