American Canyon climate

American Canyon Frost Dates and Growing Season

NOAA 1991-2020 normals for Napa CO AP, 4.4 km from American Canyon, elevation 14 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Napa CO AP. 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 March 5 and the first fall freeze around November 21, a growing season of about 256 days.

Median at 36°F
last April 17, first November 4
Median at 32°F
last March 5, first November 21
Median at 28°F
last January 23, first December 5

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 9Apr 30Apr 27Apr 22Apr 17Apr 12Apr 6Mar 30Mar 17
32°FApr 16Apr 4Mar 25Mar 14Mar 5Feb 28Feb 20Feb 8Jan 26
28°FFeb 28Feb 17Feb 6Jan 31Jan 23Jan 14Jan 6Dec 29Dec 20
24°FFeb 2Jan 21Jan 14Jan 6Dec 31Dec 27Dec 21Dec 13Dec 6
20°FJan 20Jan 10Jan 3Dec 31Dec 28Dec 20Dec 15Dec 11Dec 4
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 16Oct 24Oct 29Nov 1Nov 4Nov 6Nov 10Nov 15Nov 22
32°FNov 3Nov 8Nov 12Nov 17Nov 21Nov 25Nov 29Dec 3Dec 13
28°FNov 16Nov 22Nov 28Dec 1Dec 5Dec 12Dec 18Dec 30Jan 11
24°FNov 28Dec 2Dec 7Dec 12Dec 17Dec 24Jan 1Jan 9Jan 23
20°FDec 2Dec 6Dec 10Dec 15Dec 21Dec 28Jan 1Jan 6Jan 20
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°F230218210204199194189182171
32°F305286277268256247236225212
28°F361347337330323314306294279
24°F365365365365361353341335327
20°F365365365365365365365365363
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
92% of years
24°F or colder
52% of years
20°F or colder
11% 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
2,956
Cooling degree days, base 65°F
315
Growing degree days, base 40°F
6,492
Growing degree days, base 45°F
4,730
Growing degree days, base 50°F
3,153
Growing degree days, base 55°F
1,878
Growing degree days, base 60°F
930

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January541026
February407060
March3740113
April2793181
May15716324
June5253452
July1974519
August1584533
September4766470
October15419331
November3681113
December544032

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 4.4 km from American Canyon. 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 USW00093227 (Napa CO AP). Public domain.