Angwin climate

Angwin Frost Dates and Growing Season

NOAA 1991-2020 normals for Angwin Pacific Union College, 0.9 km from Angwin, elevation 1715 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Angwin Pacific Union College. 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 7 and the first fall freeze around December 5, a growing season of about 245 days.

Median at 36°F
last April 30, first November 15
Median at 32°F
last April 7, first December 5
Median at 28°F
last February 18, first December 30

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 15May 9May 4Apr 30Apr 26Apr 21Apr 16Apr 6
32°FApr 30Apr 23Apr 18Apr 13Apr 7Mar 31Mar 21Mar 9Feb 23
28°FApr 9Mar 30Mar 15Mar 2Feb 18Feb 3Jan 19Jan 4Dec 23
24°FFeb 26Feb 8Jan 26Jan 13Jan 1Dec 27Dec 19Dec 10Dec 5
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 22Nov 1Nov 5Nov 10Nov 15Nov 18Nov 23Nov 30Dec 5
32°FNov 14Nov 21Nov 27Dec 1Dec 5Dec 9Dec 14Dec 21Jan 1
28°FNov 29Dec 6Dec 13Dec 20Dec 30Jan 4Jan 21Feb 4Mar 4
24°FDec 4Dec 10Dec 17Dec 23Dec 31Jan 6Jan 21Feb 2Feb 24
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°F225214207201195189183173163
32°F293272261253245236229220209
28°F365364347334321306291274259
24°F365365365365365365365365347
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
83% of years
24°F or colder
20% of years
20°F or colder
0% 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
3,375
Cooling degree days, base 65°F
604
Growing degree days, base 40°F
6,388
Growing degree days, base 45°F
4,711
Growing degree days, base 50°F
3,278
Growing degree days, base 55°F
2,132
Growing degree days, base 60°F
1,240

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January574033
February482045
March448293
April3347154
May20036306
June7494470
July20155600
August21148592
September46117521
October16845347
November413298
December597020

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 0.9 km from Angwin. 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 USC00040212 (Angwin Pacific Union College). Public domain.