Penryn climate

Penryn Frost Dates and Growing Season

NOAA 1991-2020 normals for Auburn, 9.6 km from Penryn, elevation 1292 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Auburn. 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 25 and the first fall freeze around December 5, a growing season of about 286 days.

Median at 36°F
last April 5, first November 19
Median at 32°F
last February 25, first December 5
Median at 28°F
last January 13, 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°FApr 30Apr 20Apr 15Apr 10Apr 5Mar 31Mar 23Mar 14Mar 2
32°FApr 7Mar 28Mar 14Mar 3Feb 25Feb 16Feb 5Jan 27Jan 15
28°FFeb 25Feb 12Jan 31Jan 20Jan 13Jan 7Jan 2Dec 28Dec 19
24°FJan 28Jan 13Jan 8Jan 3Dec 31Dec 28Dec 22Dec 17Dec 9
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°FOct 30Nov 6Nov 12Nov 16Nov 19Nov 23Nov 27Dec 1Dec 7
32°FNov 15Nov 22Nov 28Dec 1Dec 5Dec 9Dec 13Dec 19Dec 31
28°FDec 1Dec 7Dec 12Dec 16Dec 22Dec 27Jan 1Jan 8Jan 22
24°FDec 6Dec 13Dec 19Dec 24Dec 28Dec 30Jan 3Jan 7Jan 14
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°F261248239233227220213205195
32°F330314305294286275265253236
28°F365364357351344338330318302
24°F365365365365365365363355343
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
99% of years
28°F or colder
81% of years
24°F or colder
30% of years
20°F or colder
5% 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
2,813
Cooling degree days, base 65°F
1,453
Growing degree days, base 40°F
7,786
Growing degree days, base 45°F
6,060
Growing degree days, base 50°F
4,541
Growing degree days, base 55°F
3,284
Growing degree days, base 60°F
2,270

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January556029
February428062
March3821130
April26812211
May11388442
June24222648
July1405870
August1385849
September13257695
October10380443
November3503140
December573023

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 9.6 km from Penryn. 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 USC00040383 (Auburn). Public domain.