Humboldt climate

Humboldt Frost Dates and Growing Season

NOAA 1991-2020 normals for Humboldt Wtp, 0.5 km from Humboldt, elevation 1100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Humboldt Wtp. 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 27 and the first fall freeze around October 9, a growing season of about 166 days.

Median at 36°F
last May 5, first September 29
Median at 32°F
last April 27, first October 9
Median at 28°F
last April 17, first October 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°FMay 15May 11May 9May 7May 5May 3May 1Apr 28Apr 23
32°FMay 7May 4May 1Apr 30Apr 27Apr 24Apr 21Apr 18Apr 15
28°FApr 30Apr 25Apr 22Apr 20Apr 17Apr 15Apr 13Apr 9Apr 6
24°FApr 21Apr 17Apr 14Apr 11Apr 9Apr 6Apr 4Apr 1Mar 26
20°FApr 15Apr 9Apr 6Apr 3Apr 1Mar 30Mar 24Mar 20Mar 13
16°FApr 7Apr 2Mar 30Mar 26Mar 22Mar 18Mar 15Mar 11Mar 6

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 17Sep 21Sep 24Sep 27Sep 29Oct 1Oct 4Oct 8Oct 13
32°FSep 24Sep 29Oct 2Oct 5Oct 9Oct 13Oct 17Oct 20Oct 24
28°FOct 5Oct 12Oct 16Oct 19Oct 22Oct 24Oct 26Oct 30Nov 3
24°FOct 18Oct 23Oct 26Oct 29Oct 31Nov 2Nov 4Nov 8Nov 12
20°FOct 27Nov 1Nov 3Nov 5Nov 8Nov 10Nov 13Nov 16Nov 21
16°FNov 3Nov 7Nov 9Nov 12Nov 14Nov 17Nov 21Nov 25Nov 30

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°F164159155151147143140136130
32°F183178173170166161158153147
28°F202197192189186182178174167
24°F221214210206203199195190185
20°F241233227223219216212207200
16°F258250245241236233228223216

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
7,433
Cooling degree days, base 65°F
622
Growing degree days, base 40°F
4,697
Growing degree days, base 45°F
3,646
Growing degree days, base 50°F
2,705
Growing degree days, base 55°F
1,881
Growing degree days, base 60°F
1,182

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50500
February1,23600
March972012
April560272
May23329283
June37143556
July7227685
August17157604
September15055364
October4869117
November907011
December1,32300

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 0.5 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 USC00133980 (Humboldt Wtp). Public domain.