Johnson County climate

Johnson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Clarksville 6 Ne, 6.6 km from Johnson County, elevation 850 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Clarksville 6 Ne. 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 25 and the first fall freeze around November 10, a growing season of about 232 days.

Median at 36°F
last April 7, first November 1
Median at 32°F
last March 25, first November 10
Median at 28°F
last March 12, first November 23

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 15Apr 11Apr 7Apr 4Mar 31Mar 28Mar 21
32°FApr 12Apr 5Apr 2Mar 30Mar 25Mar 22Mar 17Mar 13Mar 6
28°FMar 31Mar 24Mar 20Mar 15Mar 12Mar 9Mar 5Feb 28Feb 24
24°FMar 19Mar 13Mar 9Mar 5Mar 2Feb 27Feb 23Feb 18Feb 10
20°FMar 10Mar 4Feb 28Feb 23Feb 19Feb 13Feb 6Jan 31Jan 22
16°FMar 2Feb 23Feb 14Feb 8Feb 3Jan 30Jan 24Jan 16Jan 3

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 18Oct 23Oct 26Oct 29Nov 1Nov 3Nov 6Nov 11Nov 16
32°FOct 28Nov 1Nov 4Nov 6Nov 10Nov 14Nov 18Nov 23Nov 30
28°FNov 5Nov 9Nov 13Nov 18Nov 23Nov 27Dec 1Dec 5Dec 10
24°FNov 12Nov 19Nov 25Nov 30Dec 3Dec 8Dec 12Dec 19Dec 26
20°FNov 24Dec 1Dec 8Dec 14Dec 20Dec 26Jan 1Jan 4Jan 12
16°FDec 5Dec 14Dec 22Dec 27Jan 1Jan 5Jan 11Jan 17Jan 31

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°F232223217213209205199192184
32°F254247241236232227222216210
28°F279270264258253248243236228
24°F307296289284277271265258250
20°F335324316309304298292284272
16°F363351341334330323316307299

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
90% 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
3,577
Cooling degree days, base 65°F
1,753
Growing degree days, base 40°F
7,688
Growing degree days, base 45°F
6,201
Growing degree days, base 50°F
4,862
Growing degree days, base 55°F
3,670
Growing degree days, base 60°F
2,636

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January840017
February639135
March4625122
April20133303
May50137553
June1331780
July0474939
August0465930
September14244679
October16560371
November4574108
December747025

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 6.6 km from Johnson County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00031457 (Clarksville 6 Ne). Public domain.