Penn Valley climate

Penn Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Grass Valley #2, 10.6 km from Penn Valley, elevation 2400 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Grass Valley #2. 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 10 and the first fall freeze around November 13, a growing season of about 215 days.

Median at 36°F
last April 28, first October 31
Median at 32°F
last April 10, first November 13
Median at 28°F
last March 9, first December 1

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 20May 11May 5May 1Apr 28Apr 25Apr 22Apr 18Apr 13
32°FApr 30Apr 23Apr 18Apr 14Apr 10Apr 7Apr 3Mar 29Mar 17
28°FApr 8Apr 2Mar 25Mar 15Mar 9Mar 1Feb 25Feb 16Jan 31
24°FFeb 27Feb 16Feb 6Jan 30Jan 21Jan 13Jan 5Dec 30Dec 19
20°FJan 28Jan 19Jan 10Jan 3Dec 31Dec 29Dec 25Dec 19Dec 10
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 11Oct 18Oct 23Oct 27Oct 31Nov 2Nov 5Nov 9Nov 13
32°FOct 26Nov 1Nov 5Nov 10Nov 13Nov 17Nov 21Nov 26Dec 1
28°FNov 11Nov 18Nov 23Nov 27Dec 1Dec 5Dec 9Dec 13Dec 21
24°FNov 28Dec 3Dec 9Dec 15Dec 19Dec 26Jan 1Jan 10Jan 24
20°FDec 8Dec 16Dec 22Dec 26Dec 29Jan 1Jan 5Jan 13Jan 25
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°F204197192187182177171165157
32°F244232225220215210205198188
28°F310294283274268259249241230
24°F365362352343336329320307291
20°F365365365365365365365358349
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
84% of years
20°F or colder
25% of years
16°F or colder
2% 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
3,963
Cooling degree days, base 65°F
749
Growing degree days, base 40°F
6,020
Growing degree days, base 45°F
4,479
Growing degree days, base 50°F
3,206
Growing degree days, base 55°F
2,191
Growing degree days, base 60°F
1,380

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January67107
February573016
March544048
April4101108
May21826287
June66108493
July5256716
August5225685
September49115517
October23119267
November497059
December69403

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 10.6 km from Penn 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 USC00043573 (Grass Valley #2). Public domain.