Harney County climate

Harney County Frost Dates and Growing Season

NOAA 1991-2020 normals for Malheur Refuge Hq, 24.5 km from Harney County, elevation 4118 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Malheur Refuge Hq. 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 29 and the first fall freeze around September 18, a growing season of about 113 days.

Median at 32°F
last May 29, first September 18
Median at 28°F
last May 3, first October 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°F–––––––––
32°FJun 17Jun 12Jun 7Jun 3May 29May 22May 17May 12May 6
28°FMay 24May 15May 10May 7May 3Apr 30Apr 28Apr 24Apr 20
24°FMay 5Apr 30Apr 27Apr 24Apr 20Apr 17Apr 12Apr 8Apr 1
20°FApr 22Apr 17Apr 11Apr 6Apr 2Mar 28Mar 21Mar 15Mar 7
16°FApr 4Mar 23Mar 16Mar 10Mar 4Mar 1Feb 25Feb 19Feb 13

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°FSep 2Sep 7Sep 11Sep 15Sep 18Sep 22Sep 24Sep 29Oct 3
28°FSep 13Sep 21Sep 25Sep 28Oct 1Oct 5Oct 8Oct 12Oct 18
24°FSep 27Oct 4Oct 8Oct 12Oct 16Oct 19Oct 22Oct 26Oct 31
20°FOct 11Oct 17Oct 21Oct 25Oct 28Nov 1Nov 4Nov 9Nov 15
16°FOct 22Oct 28Nov 1Nov 4Nov 9Nov 12Nov 18Nov 23Nov 30

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°F1039689858176706556
32°F1391301241181131061019585
28°F171164158153149145139132124
24°F202194188183178173167161153
20°F240231222216209204198192182
16°F279267259253246240233225213

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
6,933
Cooling degree days, base 65°F
245
Growing degree days, base 40°F
3,714
Growing degree days, base 45°F
2,658
Growing degree days, base 50°F
1,791
Growing degree days, base 55°F
1,104
Growing degree days, base 60°F
586

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10700
February91300
March79503
April615031
May3715152
June19624286
July46125544
August6979477
September23311243
October572050
November88205
December1,13400

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 24.5 km from Harney 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 USC00355162 (Malheur Refuge Hq). Public domain.