Hanna climate

Hanna Frost Dates and Growing Season

NOAA 1991-2020 normals for Elk Mtn, 23.7 km from Hanna, elevation 7265 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Elk Mtn. 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 28 and the first fall freeze around September 13, a growing season of about 108 days.

Median at 32°F
last May 28, first September 13
Median at 28°F
last May 13, first September 26

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°F–––––––––
32°FJun 13Jun 5Jun 2May 31May 28May 25May 22May 18May 14
28°FMay 29May 23May 19May 16May 13May 11May 8May 5May 1
24°FMay 16May 11May 9May 6May 3May 1Apr 29Apr 24Apr 18
20°FMay 10May 4May 1Apr 27Apr 24Apr 19Apr 15Apr 11Apr 6
16°FMay 2Apr 25Apr 20Apr 15Apr 11Apr 8Apr 4Apr 1Mar 24

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°F–––––––––
32°FAug 30Sep 4Sep 7Sep 11Sep 13Sep 16Sep 20Sep 24Oct 1
28°FSep 9Sep 15Sep 19Sep 23Sep 26Sep 30Oct 3Oct 7Oct 12
24°FSep 21Sep 27Oct 1Oct 5Oct 8Oct 11Oct 15Oct 19Oct 24
20°FOct 2Oct 6Oct 10Oct 14Oct 18Oct 21Oct 25Oct 29Nov 3
16°FOct 8Oct 14Oct 18Oct 22Oct 26Oct 30Nov 3Nov 7Nov 12

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°F1019489837974696354
32°F129122117112108103989385
28°F154147142138133129125119111
24°F176168164159155150145140132
20°F200190184180175170166159152
16°F220211204199194189184178169

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
8,026
Cooling degree days, base 65°F
144
Growing degree days, base 40°F
3,272
Growing degree days, base 45°F
2,322
Growing degree days, base 50°F
1,535
Growing degree days, base 55°F
905
Growing degree days, base 60°F
436

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,25100
February1,09900
March97702
April756011
May503078
June20016276
July5178493
August8045430
September2825202
October631040
November95404
December1,24300

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 23.7 km from Hanna. 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 USC00482995 (Elk Mtn). Public domain.