Hailey climate

Hailey Frost Dates and Growing Season

NOAA 1991-2020 normals for Bellevue, 7.5 km from Hailey, elevation 5192 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bellevue. 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 13 and the first fall freeze around October 2, a growing season of about 139 days.

Median at 36°F
last June 2, first September 20
Median at 32°F
last May 13, first October 2
Median at 28°F
last April 28, first October 14

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 22Jun 16Jun 11Jun 6Jun 2May 30May 25May 20May 15
32°FJun 3May 25May 19May 15May 13May 9May 6May 3Apr 30
28°FMay 11May 7May 3May 1Apr 28Apr 25Apr 21Apr 17Apr 12
24°FApr 30Apr 23Apr 18Apr 13Apr 9Apr 5Mar 31Mar 25Mar 18
20°FApr 6Apr 1Mar 27Mar 21Mar 17Mar 14Mar 10Mar 7Mar 2
16°FMar 21Mar 13Mar 10Mar 7Mar 5Mar 2Feb 28Feb 23Feb 15

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 3Sep 9Sep 12Sep 16Sep 20Sep 23Sep 26Sep 29Oct 4
32°FSep 15Sep 21Sep 25Sep 29Oct 2Oct 5Oct 8Oct 12Oct 17
28°FSep 30Oct 5Oct 8Oct 11Oct 14Oct 17Oct 21Oct 24Oct 30
24°FOct 10Oct 16Oct 19Oct 23Oct 26Oct 29Nov 1Nov 4Nov 11
20°FOct 20Oct 27Oct 30Nov 2Nov 6Nov 10Nov 14Nov 18Nov 23
16°FOct 28Nov 3Nov 8Nov 12Nov 16Nov 19Nov 23Nov 26Dec 1

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°F131123117112106101969182
32°F163156150145139135129122112
28°F192184178173169164159154146
24°F225216210205200195189183174
20°F255247242236231226220214207
16°F277270264259255249244238231

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
7,012
Cooling degree days, base 65°F
434
Growing degree days, base 40°F
4,155
Growing degree days, base 45°F
3,093
Growing degree days, base 50°F
2,192
Growing degree days, base 55°F
1,451
Growing degree days, base 60°F
867

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,22800
February1,02300
March85102
April548029
May3341160
June13642360
July20197643
August22155598
September17838320
October538176
November90604
December1,22900

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 7.5 km from Hailey. 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 USC00100774 (Bellevue). Public domain.