Wallowa climate

Wallowa Frost Dates and Growing Season

NOAA 1991-2020 normals for Wallowa, 0.4 km from Wallowa, elevation 2923 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wallowa. 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 7 and the first fall freeze around September 9, a growing season of about 91 days.

Median at 32°F
last June 7, first September 9
Median at 28°F
last May 11, first September 24

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 7Jun 23Jun 18Jun 12Jun 7Jun 1May 27May 22May 14
28°FMay 29May 22May 17May 13May 11May 8May 6May 2Apr 29
24°FMay 11May 7May 4May 1Apr 28Apr 25Apr 21Apr 17Apr 11
20°FApr 27Apr 20Apr 16Apr 10Apr 6Apr 1Mar 28Mar 21Mar 13
16°FApr 3Mar 26Mar 18Mar 13Mar 8Mar 4Mar 1Feb 25Feb 16

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 24Aug 31Sep 3Sep 6Sep 9Sep 12Sep 16Sep 21Sep 27
28°FSep 5Sep 11Sep 16Sep 21Sep 24Sep 28Oct 1Oct 4Oct 8
24°FSep 19Sep 26Sep 30Oct 3Oct 5Oct 8Oct 12Oct 16Oct 21
20°FOct 2Oct 7Oct 12Oct 16Oct 20Oct 23Oct 27Oct 31Nov 7
16°FOct 16Oct 22Oct 27Oct 31Nov 4Nov 9Nov 14Nov 20Nov 26

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°F817166595347423630
32°F120112103979185797058
28°F154147142137133129124117108
24°F189177171166161157152147140
20°F227217210204198193187178168
16°F270259251246239233228220210

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
6,846
Cooling degree days, base 65°F
244
Growing degree days, base 40°F
3,809
Growing degree days, base 45°F
2,731
Growing degree days, base 50°F
1,846
Growing degree days, base 55°F
1,135
Growing degree days, base 60°F
598

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,14700
February90700
March78004
April578027
May3542149
June17522301
July41110533
August4893510
September20817269
October560049
November88703
December1,16200

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 0.4 km from Wallowa. 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 USC00358997 (Wallowa). Public domain.