Knoxville climate

Knoxville Frost Dates and Growing Season

NOAA 1991-2020 normals for Knoxville Exp Stn, 7.7 km from Knoxville, elevation 830 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Knoxville Exp Stn. 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 11 and the first fall freeze around October 28, a growing season of about 198 days.

Median at 36°F
last April 24, first October 19
Median at 32°F
last April 11, first October 28
Median at 28°F
last March 31, first November 6

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 10May 5May 1Apr 28Apr 24Apr 21Apr 18Apr 14Apr 9
32°FApr 29Apr 22Apr 19Apr 15Apr 11Apr 8Apr 5Apr 1Mar 26
28°FApr 16Apr 9Apr 5Apr 2Mar 31Mar 28Mar 24Mar 19Mar 13
24°FApr 5Mar 31Mar 26Mar 22Mar 18Mar 15Mar 11Mar 5Feb 26
20°FMar 24Mar 17Mar 12Mar 7Mar 2Feb 25Feb 19Feb 13Feb 4
16°FMar 11Mar 2Feb 24Feb 17Feb 11Feb 6Feb 1Jan 27Jan 15

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 7Oct 11Oct 13Oct 16Oct 19Oct 21Oct 24Oct 27Nov 1
32°FOct 13Oct 19Oct 22Oct 25Oct 28Oct 31Nov 1Nov 5Nov 9
28°FOct 24Oct 29Nov 1Nov 3Nov 6Nov 9Nov 12Nov 15Nov 20
24°FNov 4Nov 8Nov 12Nov 15Nov 18Nov 21Nov 26Dec 1Dec 5
20°FNov 15Nov 20Nov 25Nov 29Dec 3Dec 6Dec 13Dec 20Dec 29
16°FNov 27Dec 4Dec 11Dec 20Dec 25Dec 30Jan 3Jan 9Jan 19

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°F199192186182178173169165159
32°F220213208203198194188183176
28°F245235230225221216212207199
24°F274264257252246240235230221
20°F311299291283276269263255246
16°F341331324316309303295287273

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
3,911
Cooling degree days, base 65°F
1,364
Growing degree days, base 40°F
7,010
Growing degree days, base 45°F
5,563
Growing degree days, base 50°F
4,278
Growing degree days, base 55°F
3,154
Growing degree days, base 60°F
2,185

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January863014
February675023
March513297
April25221250
May74110502
June5268712
July0380845
August1352817
September23196622
October21934298
November522274
December763023

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 7.7 km from Knoxville. 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 USC00404946 (Knoxville Exp Stn). Public domain.