Johnson County climate

Johnson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Tecumseh 1S, 7.4 km from Johnson County, elevation 1110 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tecumseh 1S. 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 26 and the first fall freeze around October 10, a growing season of about 164 days.

Median at 36°F
last May 5, first September 30
Median at 32°F
last April 26, first October 10
Median at 28°F
last April 16, first October 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°FMay 20May 15May 11May 7May 5May 2Apr 30Apr 26Apr 22
32°FMay 11May 5May 1Apr 28Apr 26Apr 23Apr 19Apr 16Apr 12
28°FApr 30Apr 26Apr 23Apr 19Apr 16Apr 13Apr 10Apr 7Apr 2
24°FApr 21Apr 16Apr 12Apr 9Apr 6Apr 3Mar 31Mar 27Mar 21
20°FApr 11Apr 6Apr 2Mar 30Mar 27Mar 23Mar 19Mar 14Mar 9
16°FApr 2Mar 28Mar 23Mar 19Mar 15Mar 12Mar 9Mar 4Feb 28

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 16Sep 22Sep 25Sep 28Sep 30Oct 3Oct 5Oct 8Oct 12
32°FSep 25Sep 30Oct 3Oct 7Oct 10Oct 12Oct 15Oct 18Oct 23
28°FOct 3Oct 10Oct 14Oct 18Oct 20Oct 23Oct 25Oct 28Nov 1
24°FOct 14Oct 21Oct 24Oct 26Oct 29Nov 1Nov 3Nov 6Nov 12
20°FOct 24Oct 30Nov 1Nov 3Nov 6Nov 9Nov 12Nov 17Nov 24
16°FNov 1Nov 5Nov 9Nov 12Nov 16Nov 19Nov 23Nov 28Dec 3

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°F164159155152148145141135128
32°F183176171168164161157152145
28°F205197192187183180176172165
24°F226219213209204200195190184
20°F247239233228224219214208200
16°F269259253249244239235228219

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
100% 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
6,053
Cooling degree days, base 65°F
1,102
Growing degree days, base 40°F
5,725
Growing degree days, base 45°F
4,549
Growing degree days, base 50°F
3,502
Growing degree days, base 55°F
2,577
Growing degree days, base 60°F
1,775

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,27200
February1,02105
March769243
April4279141
May16469382
June17230663
July3357820
August6296755
September96123481
October38415181
November762030
December1,13101

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 7.4 km from Johnson 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 USC00258465 (Tecumseh 1S). Public domain.