Knox County climate

Knox County Frost Dates and Growing Season

NOAA 1991-2020 normals for Truscott 3 W, 20.2 km from Knox County, elevation 1571 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Truscott 3 W. 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 March 28 and the first fall freeze around November 9, a growing season of about 227 days.

Median at 36°F
last April 8, first November 1
Median at 32°F
last March 28, first November 9
Median at 28°F
last March 13, first November 20

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 26Apr 20Apr 16Apr 12Apr 8Apr 5Apr 2Mar 30Mar 23
32°FApr 14Apr 7Apr 4Mar 31Mar 28Mar 23Mar 19Mar 13Mar 7
28°FApr 2Mar 29Mar 23Mar 18Mar 13Mar 10Mar 6Mar 2Feb 24
24°FMar 20Mar 13Mar 9Mar 5Mar 1Feb 25Feb 21Feb 15Feb 6
20°FMar 10Mar 3Feb 27Feb 21Feb 16Feb 10Feb 3Jan 27Jan 15
16°FFeb 28Feb 19Feb 11Feb 5Jan 30Jan 23Jan 15Jan 3Dec 21

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 19Oct 24Oct 26Oct 29Nov 1Nov 4Nov 7Nov 11Nov 17
32°FOct 26Oct 30Nov 3Nov 6Nov 9Nov 13Nov 17Nov 22Nov 28
28°FNov 2Nov 8Nov 13Nov 16Nov 20Nov 25Nov 28Dec 1Dec 6
24°FNov 11Nov 19Nov 24Nov 28Dec 1Dec 4Dec 8Dec 13Dec 20
20°FNov 21Nov 29Dec 3Dec 9Dec 13Dec 18Dec 24Jan 1Jan 12
16°FDec 2Dec 8Dec 15Dec 20Dec 27Jan 2Jan 11Jan 21Feb 1

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°F229221215210206201197191183
32°F257246238233227223216210202
28°F276269263257252247241234225
24°F305295286281275270265258248
20°F340327319309303296288279268
16°F365365353345337329319309298

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
83% 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
2,922
Cooling degree days, base 65°F
2,456
Growing degree days, base 40°F
8,899
Growing degree days, base 45°F
7,318
Growing degree days, base 50°F
5,874
Growing degree days, base 55°F
4,578
Growing degree days, base 60°F
3,439

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January702031
February533267
March36016197
April14074397
May27249687
June1472921
July06111,076
August05871,052
September12332771
October114102463
November37311170
December661144

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 20.2 km from Knox County. 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 USC00419163 (Truscott 3 W). Public domain.