Siskiyou County climate

Siskiyou County Frost Dates and Growing Season

NOAA 1991-2020 normals for Yreka, 14.9 km from Siskiyou County, elevation 2709 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Yreka. 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 30 and the first fall freeze around October 18, a growing season of about 169 days.

Median at 36°F
last May 22, first October 3
Median at 32°F
last April 30, first October 18
Median at 28°F
last April 12, first November 1

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°FJun 13Jun 5May 31May 27May 22May 18May 14May 10May 3
32°FMay 20May 13May 7May 2Apr 30Apr 27Apr 24Apr 20Apr 14
28°FMay 3Apr 26Apr 21Apr 16Apr 12Apr 8Apr 4Mar 31Mar 22
24°FApr 13Apr 4Mar 30Mar 23Mar 16Mar 10Mar 4Feb 27Feb 17
20°FMar 12Mar 3Feb 27Feb 21Feb 13Feb 5Jan 30Jan 18Jan 4
16°FFeb 20Feb 5Jan 25Jan 17Jan 10Jan 4Dec 31Dec 25Dec 13

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 20Sep 25Sep 29Oct 1Oct 3Oct 6Oct 9Oct 12Oct 17
32°FOct 3Oct 8Oct 12Oct 15Oct 18Oct 20Oct 23Oct 27Nov 2
28°FOct 17Oct 22Oct 26Oct 29Nov 1Nov 4Nov 7Nov 12Nov 20
24°FOct 29Nov 3Nov 7Nov 12Nov 16Nov 21Nov 25Nov 30Dec 7
20°FNov 9Nov 17Nov 25Nov 30Dec 4Dec 9Dec 15Dec 23Jan 1
16°FNov 28Dec 3Dec 8Dec 13Dec 21Dec 25Dec 31Jan 5Jan 17

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°F158149143139134128122116108
32°F194185180175169165160155146
28°F230219213207202196191185177
24°F286270260250243235228218209
20°F337325314305298288281270255
16°F365364357350342336330319306

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
99% of years
16°F or colder
77% 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
4,951
Cooling degree days, base 65°F
787
Growing degree days, base 40°F
5,377
Growing degree days, base 45°F
4,068
Growing degree days, base 50°F
2,983
Growing degree days, base 55°F
2,093
Growing degree days, base 60°F
1,369

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January87700
February69002
March614022
April439195
May22730284
June82105474
July9294750
August8256713
September7695471
October3566157
November673014
December89901

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 14.9 km from Siskiyou County. 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 USC00049866 (Yreka). Public domain.