Sonora climate

Sonora Frost Dates and Growing Season

NOAA 1991-2020 normals for Sonora, 1.9 km from Sonora, elevation 1675 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sonora. 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 9 and the first fall freeze around November 9, a growing season of about 213 days.

Median at 36°F
last April 30, first October 25
Median at 32°F
last April 9, first November 9
Median at 28°F
last March 4, first November 27

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 19May 11May 6May 2Apr 30Apr 26Apr 22Apr 18Apr 11
32°FApr 30Apr 23Apr 18Apr 13Apr 9Apr 5Apr 1Mar 25Mar 15
28°FApr 8Mar 29Mar 18Mar 11Mar 4Feb 28Feb 23Feb 12Jan 31
24°FFeb 28Feb 19Feb 9Feb 3Jan 28Jan 20Jan 9Jan 1Dec 23
20°FFeb 1Jan 27Jan 17Jan 10Jan 5Dec 31Dec 28Dec 23Dec 15
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 7Oct 14Oct 17Oct 21Oct 25Oct 29Nov 1Nov 5Nov 12
32°FOct 19Oct 27Nov 1Nov 4Nov 9Nov 12Nov 17Nov 21Nov 27
28°FNov 7Nov 15Nov 19Nov 23Nov 27Dec 1Dec 5Dec 9Dec 19
24°FNov 24Dec 1Dec 6Dec 11Dec 15Dec 22Jan 1Jan 8Jan 27
20°FDec 5Dec 14Dec 20Dec 25Dec 29Jan 1Jan 8Jan 14Jan 27
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°F202194188183178173167160152
32°F244231223218213207200194186
28°F305292281272264257248239227
24°F365352341333325318309299286
20°F365365365365365365359350338
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
38% of years
16°F or colder
6% 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
3,572
Cooling degree days, base 65°F
926
Growing degree days, base 40°F
6,542
Growing degree days, base 45°F
4,927
Growing degree days, base 50°F
3,560
Growing degree days, base 55°F
2,466
Growing degree days, base 60°F
1,603

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January64309
February526023
March479067
April3562136
May17436333
June45137542
July2306769
August2272735
September36148563
October19527304
November456072
December65908

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 1.9 km from Sonora. 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 USC00048353 (Sonora). Public domain.