Humboldt climate

Humboldt Frost Dates and Growing Season

NOAA 1991-2020 normals for Humboldt, 0.8 km from Humboldt, elevation 940 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Humboldt. 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 11 and the first fall freeze around October 27, a growing season of about 195 days.

Median at 36°F
last April 23, first October 16
Median at 32°F
last April 11, first October 27
Median at 28°F
last April 2, first November 4

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 6May 1Apr 29Apr 26Apr 23Apr 20Apr 16Apr 12Apr 7
32°FApr 29Apr 23Apr 20Apr 15Apr 11Apr 8Apr 5Apr 1Mar 27
28°FApr 20Apr 13Apr 8Apr 5Apr 2Mar 31Mar 28Mar 23Mar 16
24°FApr 10Apr 3Mar 31Mar 27Mar 22Mar 18Mar 14Mar 9Mar 2
20°FApr 1Mar 25Mar 19Mar 14Mar 10Mar 7Mar 3Feb 28Feb 21
16°FMar 20Mar 12Mar 8Mar 4Mar 1Feb 25Feb 21Feb 15Feb 5

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°FSep 30Oct 5Oct 9Oct 14Oct 16Oct 19Oct 22Oct 25Oct 29
32°FOct 10Oct 17Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 9
28°FOct 20Oct 27Oct 30Nov 1Nov 4Nov 7Nov 9Nov 13Nov 19
24°FOct 29Nov 2Nov 6Nov 9Nov 13Nov 17Nov 21Nov 26Dec 1
20°FNov 4Nov 9Nov 15Nov 20Nov 23Nov 28Dec 1Dec 6Dec 13
16°FNov 15Nov 23Nov 29Dec 1Dec 5Dec 9Dec 14Dec 19Dec 26

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°F196189184179174170166161153
32°F216209204199195191187182174
28°F238231226220215211205200192
24°F262253246241236231225219209
20°F286277271264259252246239229
16°F310300294289282275270263252

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
100% of years
20°F or colder
100% of years
16°F or colder
100% 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
4,666
Cooling degree days, base 65°F
1,480
Growing degree days, base 40°F
6,756
Growing degree days, base 45°F
5,416
Growing degree days, base 50°F
4,223
Growing degree days, base 55°F
3,171
Growing degree days, base 60°F
2,259

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02905
February804016
March602474
April31720210
May102102468
June6296739
July1446910
August2395859
September43178586
October25637280
November584268
December92109

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 0.8 km from Humboldt. 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 USC00143867 (Humboldt). Public domain.