Sonora climate

Sonora Frost Dates and Growing Season

NOAA 1991-2020 normals for Sonora, 1.9 km from Sonora, elevation 2138 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 1 and the first fall freeze around November 6, a growing season of about 221 days.

Median at 36°F
last April 13, first October 28
Median at 32°F
last April 1, first November 6
Median at 28°F
last March 13, first November 16

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 29Apr 24Apr 19Apr 16Apr 13Apr 10Apr 6Apr 2Mar 26
32°FApr 20Apr 13Apr 8Apr 4Apr 1Mar 26Mar 21Mar 15Mar 8
28°FApr 7Mar 31Mar 25Mar 19Mar 13Mar 9Mar 5Feb 28Feb 22
24°FMar 23Mar 13Mar 8Mar 4Mar 1Feb 25Feb 21Feb 15Feb 7
20°FMar 7Feb 28Feb 23Feb 18Feb 11Feb 6Jan 31Jan 22Jan 7
16°FMar 1Feb 16Feb 7Feb 1Jan 27Jan 18Jan 8Jan 1Dec 16

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 12Oct 18Oct 22Oct 25Oct 28Oct 31Nov 3Nov 6Nov 13
32°FOct 24Oct 28Nov 1Nov 3Nov 6Nov 8Nov 13Nov 17Nov 24
28°FOct 31Nov 4Nov 8Nov 12Nov 16Nov 19Nov 24Dec 1Dec 5
24°FNov 8Nov 15Nov 20Nov 25Nov 29Dec 2Dec 6Dec 12Dec 19
20°FNov 20Nov 27Dec 2Dec 6Dec 11Dec 18Dec 24Jan 1Jan 13
16°FDec 2Dec 7Dec 13Dec 21Dec 28Jan 1Jan 9Jan 19Feb 5

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°F221212207203199195190185177
32°F249238232226221215210205197
28°F274266259252246241235228218
24°F304291284279273267261254245
20°F342328320311304297289282271
16°F365365356346338330323313302

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
98% of years
16°F or colder
76% 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
2,263
Cooling degree days, base 65°F
2,567
Growing degree days, base 40°F
9,509
Growing degree days, base 45°F
7,822
Growing degree days, base 50°F
6,271
Growing degree days, base 55°F
4,873
Growing degree days, base 60°F
3,636

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January593148
February4093100
March23927281
April80110483
May8310767
June0493943
July05751,040
August05641,029
September5347792
October76124516
November30213205
December553167

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.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00418449 (Sonora). Public domain.