Trinity County climate

Trinity County Frost Dates and Growing Season

NOAA 1991-2020 normals for Big Bar 4 E, 12.8 km from Trinity County, elevation 1253 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Big Bar 4 E. 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 16 and the first fall freeze around October 31, a growing season of about 197 days.

Median at 36°F
last May 6, first October 14
Median at 32°F
last April 16, first October 31
Median at 28°F
last March 17, first November 19

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 29May 19May 14May 10May 6May 4May 1Apr 27Apr 21
32°FMay 3Apr 28Apr 24Apr 20Apr 16Apr 11Apr 7Apr 1Mar 23
28°FApr 16Apr 5Mar 31Mar 24Mar 17Mar 10Feb 28Feb 20Feb 2
24°FMar 8Feb 26Feb 16Feb 7Jan 31Jan 19Jan 7Dec 28Dec 12
20°FFeb 10Jan 29Jan 21Jan 10Jan 4Dec 30Dec 21Dec 9Nov 29
16°FJan 24Jan 17Jan 1Dec 26Dec 21Dec 16Dec 8Dec 3Nov 29

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 27Oct 2Oct 6Oct 10Oct 14Oct 17Oct 22Oct 26Nov 1
32°FOct 13Oct 18Oct 23Oct 27Oct 31Nov 3Nov 9Nov 17Nov 26
28°FOct 24Oct 31Nov 4Nov 12Nov 19Nov 24Dec 1Dec 9Dec 20
24°FNov 7Nov 17Nov 26Dec 2Dec 9Dec 16Dec 27Jan 6Jan 28
20°FNov 21Nov 29Dec 5Dec 13Dec 23Dec 31Jan 7Jan 19Jan 30
16°FNov 27Dec 1Dec 5Dec 12Dec 17Dec 23Dec 30Jan 4Jan 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°F182173168163157152148142129
32°F231218210203197191185178170
28°F296276265254245236227217205
24°F364346333323313305292276257
20°F365365365365365357344332318
16°F365365365365365365365365357

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
88% of years
20°F or colder
41% of years
16°F or colder
14% 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
3,868
Cooling degree days, base 65°F
888
Growing degree days, base 40°F
6,248
Growing degree days, base 45°F
4,712
Growing degree days, base 50°F
3,431
Growing degree days, base 55°F
2,384
Growing degree days, base 60°F
1,547

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January71502
February554012
March482066
April3353153
May16240346
June48115518
July3308770
August2277739
September39132543
October24614242
November534035
December74704

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 12.8 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 USC00040738 (Big Bar 4 E). Public domain.