Potter Valley climate

Potter Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Potter Valley Powerhouse, 4.6 km from Potter Valley, elevation 1018 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Potter Valley Powerhouse. 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 8 and the first fall freeze around November 6, a growing season of about 211 days.

Median at 36°F
last May 2, first October 21
Median at 32°F
last April 8, first November 6
Median at 28°F
last February 28, first November 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°FMay 25May 17May 11May 6May 2Apr 29Apr 25Apr 21Apr 15
32°FApr 29Apr 22Apr 17Apr 12Apr 8Apr 4Mar 29Mar 22Mar 11
28°FApr 2Mar 21Mar 11Mar 4Feb 28Feb 23Feb 17Feb 8Jan 25
24°FFeb 28Feb 20Feb 11Feb 1Jan 26Jan 15Jan 4Dec 27Dec 17
20°FJan 30Jan 21Jan 12Jan 4Jan 1Dec 28Dec 22Dec 16Dec 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 2Oct 8Oct 13Oct 17Oct 21Oct 26Oct 31Nov 3Nov 6
32°FOct 20Oct 27Nov 1Nov 3Nov 6Nov 9Nov 12Nov 17Nov 24
28°FNov 3Nov 8Nov 13Nov 18Nov 22Nov 26Dec 1Dec 4Dec 12
24°FNov 17Nov 25Nov 30Dec 3Dec 7Dec 12Dec 18Dec 29Jan 5
20°FDec 1Dec 4Dec 10Dec 16Dec 20Dec 28Jan 2Jan 6Jan 17
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°F193186181176171165159151141
32°F243233224218211205199193184
28°F307291282274268261253243231
24°F359343335328321313304292278
20°F365365365365365360349339333
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
90% of years
20°F or colder
46% of years
16°F or colder
9% 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
3,088
Cooling degree days, base 65°F
947
Growing degree days, base 40°F
7,010
Growing degree days, base 45°F
5,311
Growing degree days, base 50°F
3,836
Growing degree days, base 55°F
2,634
Growing degree days, base 60°F
1,681

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January584019
February451049
March3901121
April2825190
May13643374
June39142554
July2303766
August3263725
September22157585
October15433347
November413092
December612015

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 4.6 km from Potter Valley. 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 USC00047109 (Potter Valley Powerhouse). Public domain.