San Manuel climate

San Manuel Frost Dates and Growing Season

NOAA 1991-2020 normals for San Manuel, 0.2 km from San Manuel, elevation 3420 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for San Manuel. 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 4 and the first fall freeze around December 8, a growing season of about 306 days.

Median at 36°F
last March 1, first November 25
Median at 32°F
last February 4, first December 8
Median at 28°F
last January 10, first December 22

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°FMar 30Mar 17Mar 10Mar 6Mar 1Feb 25Feb 19Feb 13Feb 2
32°FMar 2Feb 23Feb 16Feb 10Feb 4Feb 1Jan 23Jan 13Jan 5
28°FFeb 11Feb 4Jan 29Jan 18Jan 10Jan 5Dec 31Dec 26Dec 17
24°FFeb 3Jan 24Jan 12Jan 6Jan 3Dec 31Dec 27Dec 22Dec 17
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°FNov 9Nov 15Nov 19Nov 22Nov 25Nov 29Dec 3Dec 7Dec 11
32°FNov 20Nov 26Dec 1Dec 5Dec 8Dec 12Dec 16Dec 20Dec 28
28°FDec 3Dec 9Dec 14Dec 18Dec 22Dec 27Jan 1Jan 8Jan 25
24°FDec 8Dec 17Dec 22Dec 27Dec 31Jan 4Jan 7Jan 21Jan 31
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°F299290281275268262256249236
32°F340331323313306300293284274
28°F365365359353346340334327314
24°F365365365365365365365361345
20°F365365365365365365365365365
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
78% of years
24°F or colder
22% of years
20°F or colder
1% 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
1,942
Cooling degree days, base 65°F
2,588
Growing degree days, base 40°F
9,790
Growing degree days, base 45°F
8,027
Growing degree days, base 50°F
6,380
Growing degree days, base 55°F
4,918
Growing degree days, base 60°F
3,655

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January496052
February3540114
March2129271
April7269448
May12274727
June05501,000
July06001,065
August05411,006
September0386835
October39147574
November25313231
December505057

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 0.2 km from San Manuel. 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 USC00027530 (San Manuel). Public domain.