Sewanee climate

Sewanee Frost Dates and Growing Season

NOAA 1991-2020 normals for Sewanee, 0.3 km from Sewanee, elevation 1928 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sewanee. 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 2 and the first fall freeze around November 4, a growing season of about 216 days.

Median at 36°F
last April 13, first October 25
Median at 32°F
last April 2, first November 4
Median at 28°F
last March 23, first November 16

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 30Apr 24Apr 20Apr 17Apr 13Apr 10Apr 6Apr 3Mar 29
32°FApr 18Apr 11Apr 8Apr 5Apr 2Mar 30Mar 27Mar 22Mar 16
28°FApr 7Apr 3Mar 31Mar 27Mar 23Mar 19Mar 16Mar 10Mar 4
24°FMar 31Mar 23Mar 19Mar 15Mar 11Mar 6Mar 2Feb 26Feb 20
20°FMar 18Mar 12Mar 7Mar 3Feb 27Feb 23Feb 19Feb 13Feb 4
16°FMar 7Mar 1Feb 25Feb 20Feb 15Feb 10Feb 4Jan 30Jan 20

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 13Oct 17Oct 20Oct 23Oct 25Oct 27Oct 30Nov 1Nov 6
32°FOct 22Oct 26Oct 30Nov 1Nov 4Nov 7Nov 10Nov 15Nov 22
28°FNov 1Nov 5Nov 8Nov 12Nov 16Nov 20Nov 25Nov 30Dec 5
24°FNov 10Nov 17Nov 21Nov 26Nov 30Dec 3Dec 6Dec 12Dec 21
20°FNov 22Nov 29Dec 3Dec 7Dec 12Dec 18Dec 24Dec 30Jan 6
16°FDec 2Dec 9Dec 18Dec 24Dec 29Jan 2Jan 5Jan 12Jan 20

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°F214207202198193189184179172
32°F240232225221216212208203196
28°F263254247243238233228221214
24°F289279273268261256250243235
20°F314305298293287282276269259
16°F336328321315310305299293282

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
3,865
Cooling degree days, base 65°F
1,118
Growing degree days, base 40°F
6,867
Growing degree days, base 45°F
5,403
Growing degree days, base 50°F
4,084
Growing degree days, base 55°F
2,928
Growing degree days, base 60°F
1,941

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January862019
February683028
March5004112
April24220261
May8687469
June6213657
July0315780
August1298763
September32153572
October21226300
November485291
December756034

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 0.3 km from Sewanee. 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 USC00408184 (Sewanee). Public domain.