Etna climate

Etna Frost Dates and Growing Season

NOAA 1991-2020 normals for Callahan, 14.5 km from Etna, elevation 3085 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Callahan. 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 20 and the first fall freeze around October 5, a growing season of about 135 days.

Median at 36°F
last June 11, first September 17
Median at 32°F
last May 20, first October 5
Median at 28°F
last April 28, 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°FJul 2Jun 23Jun 18Jun 15Jun 11Jun 8Jun 4May 31May 24
32°FJun 12Jun 5May 31May 25May 20May 16May 11May 7May 2
28°FMay 21May 11May 6May 2Apr 28Apr 24Apr 20Apr 14Apr 6
24°FApr 27Apr 15Apr 9Apr 4Mar 31Mar 27Mar 20Mar 13Feb 28
20°FMar 29Mar 18Mar 8Mar 1Feb 25Feb 19Feb 10Feb 1Jan 17
16°FFeb 26Feb 17Feb 5Jan 29Jan 19Jan 12Jan 6Dec 31Dec 19

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 4Sep 9Sep 12Sep 15Sep 17Sep 20Sep 24Sep 28Oct 3
32°FSep 20Sep 26Sep 29Oct 2Oct 5Oct 8Oct 12Oct 15Oct 22
28°FOct 5Oct 10Oct 14Oct 19Oct 22Oct 27Oct 31Nov 3Nov 10
24°FOct 21Oct 27Nov 1Nov 4Nov 7Nov 11Nov 16Nov 22Nov 29
20°FNov 4Nov 12Nov 18Nov 22Nov 27Dec 1Dec 5Dec 12Dec 23
16°FNov 21Nov 30Dec 4Dec 9Dec 16Dec 21Dec 28Jan 3Jan 15

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°F1191111071019692888173
32°F159151144140135130125117107
28°F201193187181176171165158147
24°F255242232225217211206197187
20°F318305295285277269260250234
16°F364354345336331323312302287

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
91% 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
5,006
Cooling degree days, base 65°F
423
Growing degree days, base 40°F
4,922
Growing degree days, base 45°F
3,577
Growing degree days, base 50°F
2,478
Growing degree days, base 55°F
1,609
Growing degree days, base 60°F
929

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January84801
February66603
March608019
April456075
May27011225
June10949392
July15180631
August16140589
September10240390
October3762135
November668016
December87402

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 14.5 km from Etna. 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 USC00041316 (Callahan). Public domain.