Trinity County climate

Trinity County Frost Dates and Growing Season

NOAA 1991-2020 normals for Groveton, 12 km from Trinity County, elevation 350 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Groveton. 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 March 2 and the first fall freeze around November 26, a growing season of about 267 days.

Median at 36°F
last March 17, first November 11
Median at 32°F
last March 2, first November 26
Median at 28°F
last February 6, first December 12

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 7Apr 2Mar 27Mar 22Mar 17Mar 13Mar 9Mar 3Feb 25
32°FMar 24Mar 16Mar 11Mar 6Mar 2Feb 28Feb 21Feb 14Feb 1
28°FMar 10Mar 3Feb 26Feb 16Feb 6Jan 31Jan 26Jan 20Jan 7
24°FFeb 28Feb 9Feb 1Jan 26Jan 19Jan 14Jan 7Jan 1Dec 22
20°FFeb 7Jan 27Jan 21Jan 14Jan 9Jan 5Jan 2Dec 31Dec 23
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 27Nov 1Nov 4Nov 7Nov 11Nov 14Nov 19Nov 25Dec 1
32°FNov 4Nov 10Nov 16Nov 21Nov 26Dec 1Dec 4Dec 9Dec 19
28°FNov 15Nov 24Dec 1Dec 5Dec 12Dec 19Dec 26Jan 3Jan 13
24°FNov 30Dec 10Dec 20Dec 25Dec 31Jan 3Jan 9Jan 16Jan 28
20°FDec 18Dec 25Dec 30Jan 1Jan 5Jan 8Jan 14Jan 20Feb 1
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°F266256248243238232227221213
32°F302290280273267261254247238
28°F345334323314305297288278264
24°F365365359352344337330320302
20°F365365365365365365364355341
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
98% of years
24°F or colder
74% of years
20°F or colder
29% of years
16°F or colder
6% 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
1,673
Cooling degree days, base 65°F
2,863
Growing degree days, base 40°F
10,349
Growing degree days, base 45°F
8,598
Growing degree days, base 50°F
6,936
Growing degree days, base 55°F
5,415
Growing degree days, base 60°F
4,057

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January4636113
February30212170
March18746339
April46142546
May1328792
June0492942
July05911,055
August06001,064
September0425874
October45180602
November21232294
December41510145

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 12 km from Trinity County. 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 USC00413778 (Groveton). Public domain.