Mount Shasta climate

Mount Shasta Frost Dates and Growing Season

NOAA 1991-2020 normals for Mt Shasta, 1.4 km from Mount Shasta, elevation 3613 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mt Shasta. 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 May 15 and the first fall freeze around October 6, a growing season of about 143 days.

Median at 36°F
last June 6, first September 19
Median at 32°F
last May 15, first October 6
Median at 28°F
last April 29, first October 25

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 27Jun 20Jun 15Jun 10Jun 6Jun 2May 30May 25May 19
32°FJun 5May 30May 23May 19May 15May 12May 9May 4Apr 29
28°FMay 14May 10May 6May 2Apr 29Apr 26Apr 22Apr 18Apr 11
24°FApr 30Apr 24Apr 19Apr 14Apr 9Apr 5Apr 2Mar 25Mar 16
20°FApr 11Apr 3Mar 27Mar 21Mar 15Mar 9Mar 3Feb 25Feb 12
16°FMar 16Mar 5Feb 27Feb 22Feb 16Feb 8Feb 1Jan 21Jan 4

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 3Sep 9Sep 12Sep 15Sep 19Sep 22Sep 25Sep 30Oct 5
32°FSep 20Sep 26Sep 30Oct 2Oct 6Oct 9Oct 14Oct 18Oct 24
28°FOct 6Oct 13Oct 18Oct 22Oct 25Oct 28Nov 1Nov 4Nov 9
24°FOct 24Oct 28Nov 1Nov 4Nov 7Nov 11Nov 14Nov 19Nov 24
20°FNov 3Nov 7Nov 13Nov 16Nov 21Nov 24Nov 28Dec 3Dec 12
16°FNov 13Nov 20Nov 25Dec 1Dec 4Dec 9Dec 15Dec 22Jan 6

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°F12711911210710196918474
32°F167158152147143138132125115
28°F204194189184179174169163154
24°F240231223217210204199193184
20°F286275265257250242235227217
16°F338323312304296288279269256

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
99% 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
5,745
Cooling degree days, base 65°F
285
Growing degree days, base 40°F
4,245
Growing degree days, base 45°F
3,054
Growing degree days, base 50°F
2,092
Growing degree days, base 55°F
1,320
Growing degree days, base 60°F
717

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January90500
February76000
March71808
April553043
May3417173
June15135339
July28123561
August3693523
September14426336
October4381102
November73507
December93600

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 1.4 km from Mount Shasta. 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 USC00045983 (Mt Shasta). Public domain.