Johnson County climate

Johnson County Frost Dates and Growing Season

NOAA 1991-2020 normals for Billy Creek, 15.1 km from Johnson County, elevation 4975 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Billy Creek. 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 May 19 and the first fall freeze around September 21, a growing season of about 123 days.

Median at 36°F
last June 2, first September 12
Median at 32°F
last May 19, first September 21
Median at 28°F
last May 8, first September 30

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°FJun 20Jun 13Jun 9Jun 5Jun 2May 31May 28May 24May 19
32°FMay 31May 28May 25May 22May 19May 17May 14May 11May 7
28°FMay 23May 18May 14May 11May 8May 5May 3Apr 30Apr 26
24°FMay 12May 7May 3Apr 30Apr 28Apr 25Apr 21Apr 17Apr 12
20°FMay 2Apr 28Apr 24Apr 20Apr 16Apr 12Apr 9Apr 6Apr 1
16°FApr 24Apr 16Apr 12Apr 8Apr 5Apr 2Mar 30Mar 24Mar 17

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°FAug 29Sep 2Sep 6Sep 9Sep 12Sep 14Sep 17Sep 20Sep 24
32°FSep 6Sep 12Sep 16Sep 19Sep 21Sep 24Sep 26Sep 29Oct 4
28°FSep 16Sep 22Sep 24Sep 27Sep 30Oct 2Oct 5Oct 9Oct 14
24°FSep 25Sep 29Oct 2Oct 6Oct 9Oct 13Oct 16Oct 19Oct 24
20°FOct 3Oct 8Oct 12Oct 16Oct 19Oct 21Oct 24Oct 28Nov 1
16°FOct 11Oct 16Oct 20Oct 23Oct 26Oct 29Nov 1Nov 5Nov 11

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°F12011410910510096928679
32°F143136131127123120115110103
28°F162157153149145141137132125
24°F185179173169165161157154147
20°F206199193189185180174171163
16°F228219213208204198193187180

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
7,516
Cooling degree days, base 65°F
452
Growing degree days, base 40°F
3,994
Growing degree days, base 45°F
2,975
Growing degree days, base 50°F
2,123
Growing degree days, base 55°F
1,424
Growing degree days, base 60°F
866

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,22900
February1,06001
March913010
April676137
May4206142
June14954364
July35193623
August52156571
September23142294
October615270
November921011
December1,21700

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 15.1 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 USC00480740 (Billy Creek). Public domain.