Johnson climate

Johnson Frost Dates and Growing Season

NOAA 1991-2020 normals for Johnson, 0.5 km from Johnson, elevation 3330 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Johnson. 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 19 and the first fall freeze around October 23, a growing season of about 186 days.

Median at 36°F
last April 30, first October 15
Median at 32°F
last April 19, first October 23
Median at 28°F
last April 9, first November 1

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 11May 8May 5May 2Apr 30Apr 27Apr 24Apr 20Apr 17
32°FMay 3Apr 29Apr 25Apr 21Apr 19Apr 17Apr 14Apr 10Apr 5
28°FApr 23Apr 18Apr 15Apr 12Apr 9Apr 5Apr 3Mar 31Mar 24
24°FApr 13Apr 7Apr 4Apr 1Mar 29Mar 25Mar 21Mar 16Mar 10
20°FApr 3Mar 29Mar 23Mar 19Mar 15Mar 11Mar 8Mar 4Feb 28
16°FMar 22Mar 15Mar 10Mar 7Mar 3Mar 1Feb 25Feb 20Feb 11

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 2Oct 6Oct 10Oct 12Oct 15Oct 17Oct 20Oct 23Oct 26
32°FOct 10Oct 15Oct 18Oct 21Oct 23Oct 26Oct 29Nov 1Nov 5
28°FOct 19Oct 24Oct 27Oct 31Nov 1Nov 4Nov 7Nov 10Nov 14
24°FOct 27Nov 1Nov 3Nov 7Nov 10Nov 12Nov 16Nov 19Nov 23
20°FNov 1Nov 7Nov 12Nov 15Nov 18Nov 21Nov 25Nov 28Dec 3
16°FNov 8Nov 14Nov 20Nov 23Nov 27Nov 30Dec 3Dec 8Dec 14

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°F184179174171167163159155149
32°F205198193189186182178174167
28°F226218213210206202198193186
24°F248241235231225221216211205
20°F269262256251247242236231222
16°F294285279273268263256251241

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
4,773
Cooling degree days, base 65°F
1,451
Growing degree days, base 40°F
6,591
Growing degree days, base 45°F
5,260
Growing degree days, base 50°F
4,089
Growing degree days, base 55°F
3,070
Growing degree days, base 60°F
2,195

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January96703
February788012
March615164
April3569175
May12493441
June11305744
July1452916
August2380843
September48186591
October29226248
November626148
December94405

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 0.5 km from Johnson. 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 USC00144114 (Johnson). Public domain.