Elmore County climate

Elmore County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hill City 1 W, 32.6 km from Elmore County, elevation 5100 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hill City 1 W. 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 June 16 and the first fall freeze around September 6, a growing season of about 80 days.

Median at 32°F
last June 16, first September 6
Median at 28°F
last May 30, first September 18

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°FJul 3Jun 27Jun 23Jun 19Jun 16Jun 12Jun 8Jun 5May 31
28°FJun 21Jun 14Jun 8Jun 3May 30May 23May 17May 12May 6
24°FMay 30May 16May 11May 7May 3Apr 30Apr 26Apr 21Apr 15
20°FMay 3Apr 26Apr 19Apr 15Apr 11Apr 7Apr 5Apr 1Mar 28
16°FApr 11Apr 5Apr 2Mar 31Mar 28Mar 25Mar 21Mar 15Mar 9

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 20Aug 28Sep 1Sep 3Sep 6Sep 8Sep 12Sep 16Sep 22
28°FSep 2Sep 7Sep 11Sep 15Sep 18Sep 22Sep 26Oct 1Oct 5
24°FSep 10Sep 18Sep 22Sep 26Sep 29Oct 2Oct 5Oct 9Oct 15
20°FSep 22Sep 28Oct 2Oct 6Oct 11Oct 16Oct 20Oct 26Nov 2
16°FOct 4Oct 11Oct 17Oct 21Oct 26Oct 30Nov 3Nov 8Nov 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°F766863595450453932
32°F1039590858075706457
28°F136126119114109104989182
24°F170162156151145140134128116
20°F205195189183178173167160149
16°F235227221216211206200194185

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
8,513
Cooling degree days, base 65°F
182
Growing degree days, base 40°F
3,238
Growing degree days, base 45°F
2,313
Growing degree days, base 50°F
1,547
Growing degree days, base 55°F
934
Growing degree days, base 60°F
479

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,42300
February1,21100
March1,04000
April704011
May465090
June24012238
July6091496
August7372464
September2698213
October640034
November1,01001
December1,37900

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 32.6 km from Elmore 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 USC00104268 (Hill City 1 W). Public domain.