Santa Rosa climate

Santa Rosa Frost Dates and Growing Season

NOAA 1991-2020 normals for Santa Rosa, 4.1 km from Santa Rosa, elevation 4650 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Santa Rosa. 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 April 20 and the first fall freeze around October 23, a growing season of about 183 days.

Median at 36°F
last May 2, first October 12
Median at 32°F
last April 20, first October 23
Median at 28°F
last April 4, first November 1

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 15May 10May 7May 4May 2Apr 30Apr 27Apr 23Apr 17
32°FMay 6May 1Apr 27Apr 23Apr 20Apr 17Apr 13Apr 9Apr 3
28°FApr 24Apr 16Apr 12Apr 8Apr 4Apr 1Mar 30Mar 25Mar 18
24°FApr 8Apr 2Mar 29Mar 23Mar 18Mar 15Mar 11Mar 7Mar 2
20°FMar 23Mar 17Mar 13Mar 9Mar 6Mar 2Feb 27Feb 22Feb 16
16°FMar 12Mar 5Feb 28Feb 24Feb 20Feb 15Feb 10Feb 3Jan 25

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°FSep 29Oct 4Oct 7Oct 10Oct 12Oct 15Oct 18Oct 21Oct 24
32°FOct 10Oct 14Oct 17Oct 20Oct 23Oct 25Oct 28Oct 31Nov 3
28°FOct 18Oct 22Oct 26Oct 29Nov 1Nov 2Nov 4Nov 7Nov 11
24°FOct 25Oct 31Nov 3Nov 5Nov 8Nov 11Nov 14Nov 17Nov 22
20°FOct 31Nov 5Nov 11Nov 14Nov 18Nov 21Nov 24Nov 28Dec 4
16°FNov 7Nov 15Nov 20Nov 24Nov 28Dec 1Dec 6Dec 12Dec 22

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°F180173169165162158154149143
32°F203197192187183179175170163
28°F228220215211207203198192185
24°F255248241236232227222216208
20°F282273267261257252248242233
16°F316305296289283276270262253

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
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% 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
3,674
Cooling degree days, base 65°F
1,278
Growing degree days, base 40°F
7,000
Growing degree days, base 45°F
5,496
Growing degree days, base 50°F
4,179
Growing degree days, base 55°F
3,039
Growing degree days, base 60°F
2,073

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January77006
February610015
March4531102
April23510244
May6992490
June1301750
July0380845
August0330795
September24149575
October21015285
November523165
December77808

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 4.1 km from Santa Rosa. 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 USC00298107 (Santa Rosa). Public domain.