Windsor climate

Windsor Frost Dates and Growing Season

NOAA 1991-2020 normals for Santa Rosa Sonoma CO AP, 4.8 km from Windsor, elevation 114 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Santa Rosa Sonoma CO AP. 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 March 2 and the first fall freeze around November 20, a growing season of about 262 days.

Median at 36°F
last April 12, first November 3
Median at 32°F
last March 2, first November 20
Median at 28°F
last January 23, first December 5

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°FMay 1Apr 26Apr 22Apr 18Apr 12Apr 8Apr 3Mar 29Mar 17
32°FApr 2Mar 24Mar 14Mar 7Mar 2Feb 26Feb 21Feb 11Jan 27
28°FFeb 23Feb 14Feb 5Jan 30Jan 23Jan 14Jan 3Dec 29Dec 20
24°FJan 27Jan 18Jan 10Jan 4Dec 31Dec 28Dec 21Dec 14Dec 6
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°FOct 16Oct 22Oct 27Oct 31Nov 3Nov 7Nov 10Nov 14Nov 21
32°FNov 1Nov 7Nov 12Nov 16Nov 20Nov 24Nov 28Dec 3Dec 10
28°FNov 15Nov 22Nov 27Dec 1Dec 5Dec 9Dec 16Dec 28Jan 7
24°FNov 29Dec 2Dec 8Dec 13Dec 19Dec 25Jan 1Jan 5Jan 17
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°F237225218211206200194187177
32°F307290278269262255247238223
28°F361345337330321314308299284
24°F365365365365365357348340329
20°F365365365365365365365365364
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
100% of years
28°F or colder
91% of years
24°F or colder
45% of years
20°F or colder
9% 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
2,904
Cooling degree days, base 65°F
410
Growing degree days, base 40°F
6,639
Growing degree days, base 45°F
4,874
Growing degree days, base 50°F
3,302
Growing degree days, base 55°F
2,031
Growing degree days, base 60°F
1,068

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January536025
February405063
March3651125
April2714191
May15621331
June4574479
July1697546
August12105558
September3782495
October14126351
November3681114
December552027

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 4.8 km from Windsor. 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 USW00023213 (Santa Rosa Sonoma CO AP). Public domain.