Clearlake climate

Clearlake Frost Dates and Growing Season

NOAA 1991-2020 normals for Clearlake 4 Se, 6.3 km from Clearlake, elevation 1349 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Clearlake 4 Se. 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 6, a growing season of about 209 days.

Median at 36°F
last April 30, first October 27
Median at 32°F
last April 10, first November 6
Median at 28°F
last March 14, first November 21

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 16May 10May 6May 2Apr 30Apr 27Apr 24Apr 20Apr 14
32°FApr 30Apr 23Apr 18Apr 14Apr 10Apr 7Apr 4Mar 31Mar 24
28°FApr 7Mar 31Mar 27Mar 21Mar 14Mar 9Mar 2Feb 25Feb 12
24°FMar 8Feb 28Feb 23Feb 15Feb 7Jan 30Jan 22Jan 11Dec 29
20°FFeb 14Feb 1Jan 26Jan 20Jan 11Jan 4Dec 29Dec 21Dec 11
16°FJan 25Jan 18Jan 11Jan 4Dec 31Dec 24Dec 18Dec 12Dec 8

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 17Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 7
32°FOct 24Oct 29Nov 1Nov 4Nov 6Nov 9Nov 11Nov 14Nov 20
28°FNov 4Nov 10Nov 13Nov 17Nov 21Nov 24Nov 28Dec 1Dec 8
24°FNov 17Nov 25Dec 1Dec 3Dec 6Dec 11Dec 18Dec 29Jan 11
20°FDec 1Dec 6Dec 11Dec 17Dec 22Dec 30Jan 4Jan 14Jan 30
16°FDec 5Dec 10Dec 13Dec 20Dec 26Dec 31Jan 3Jan 11Jan 23

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°F196190186181178173169164155
32°F231224218213209204199194186
28°F291276264257250245239231222
24°F348334326318309301293282269
20°F365365365365357348339333320
16°F365365365365365365365365355

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
96% of years
20°F or colder
58% of years
16°F or colder
16% 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
3,707
Cooling degree days, base 65°F
788
Growing degree days, base 40°F
6,260
Growing degree days, base 45°F
4,658
Growing degree days, base 50°F
3,335
Growing degree days, base 55°F
2,279
Growing degree days, base 60°F
1,439

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January66006
February540019
March512057
April3651124
May21320281
June50120521
July3271733
August3233694
September37122536
October19822294
November465062
December66007

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 6.3 km from Clearlake. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00041806 (Clearlake 4 Se). Public domain.