Santa Rosa climate

Santa Rosa Frost Dates and Growing Season

NOAA 1991-2020 normals for Arizona City, 55.8 km from Santa Rosa, elevation 1525 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Arizona City. 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 28 and the first fall freeze around November 21, a growing season of about 266 days.

Median at 36°F
last March 17, first November 12
Median at 32°F
last February 28, first November 21
Median at 28°F
last February 6, first December 4

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 4Mar 29Mar 25Mar 20Mar 17Mar 13Mar 10Mar 5Feb 27
32°FMar 14Mar 8Mar 5Mar 2Feb 28Feb 24Feb 19Feb 12Feb 3
28°FMar 1Feb 23Feb 17Feb 11Feb 6Feb 1Jan 26Jan 20Jan 10
24°FFeb 14Feb 5Jan 31Jan 22Jan 16Jan 10Jan 5Dec 30Dec 19
20°FFeb 2Jan 25Jan 19Jan 11Jan 5Jan 2Dec 28Dec 20Dec 8
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 25Nov 1Nov 5Nov 8Nov 12Nov 14Nov 17Nov 20Nov 24
32°FNov 5Nov 11Nov 15Nov 18Nov 21Nov 24Nov 27Dec 1Dec 6
28°FNov 16Nov 22Nov 27Nov 30Dec 4Dec 7Dec 11Dec 15Dec 21
24°FNov 27Dec 3Dec 9Dec 13Dec 18Dec 22Dec 27Jan 3Jan 17
20°FDec 5Dec 12Dec 21Dec 27Jan 1Jan 3Jan 9Jan 18Jan 28
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°F259252247242238233229223214
32°F294283276271266261257251243
28°F333321313306300294287278270
24°F365358348342336330323316305
20°F365365365365365365357345334
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
100% of years
24°F or colder
89% of years
20°F or colder
40% of years
16°F or colder
4% 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
1,839
Cooling degree days, base 65°F
3,285
Growing degree days, base 40°F
10,587
Growing degree days, base 45°F
8,825
Growing degree days, base 50°F
7,171
Growing degree days, base 55°F
5,685
Growing degree days, base 60°F
4,394

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January488064
February3321126
March18719304
April57105499
May7320778
June05981,048
July07591,224
August07301,195
September1531981
October27205644
November23315252
December508056

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 55.8 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 USC00020404 (Arizona City). Public domain.