Umatilla County climate

Umatilla County Frost Dates and Growing Season

NOAA 1991-2020 normals for Pendleton, 14.2 km from Umatilla County, elevation 1515 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Pendleton. 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 April 26 and the first fall freeze around October 16, a growing season of about 174 days.

Median at 36°F
last May 9, first October 4
Median at 32°F
last April 26, first October 16
Median at 28°F
last April 1, first October 28

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°FMay 26May 19May 15May 12May 9May 6May 3Apr 30Apr 26
32°FMay 10May 5May 2Apr 28Apr 26Apr 22Apr 18Apr 13Apr 7
28°FApr 26Apr 18Apr 12Apr 5Apr 1Mar 29Mar 24Mar 18Mar 10
24°FApr 1Mar 25Mar 17Mar 12Mar 8Mar 4Feb 28Feb 21Feb 13
20°FMar 11Mar 4Feb 28Feb 23Feb 19Feb 13Feb 5Jan 25Jan 9
16°FMar 2Feb 25Feb 19Feb 12Feb 2Jan 26Jan 16Jan 6Dec 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°FSep 21Sep 25Sep 30Oct 2Oct 4Oct 7Oct 9Oct 12Oct 17
32°FOct 1Oct 6Oct 9Oct 13Oct 16Oct 18Oct 22Oct 26Nov 1
28°FOct 12Oct 17Oct 22Oct 25Oct 28Oct 31Nov 4Nov 10Nov 19
24°FOct 22Oct 28Nov 1Nov 7Nov 11Nov 16Nov 21Nov 27Dec 3
20°FOct 30Nov 8Nov 14Nov 22Nov 26Dec 1Dec 6Dec 14Dec 25
16°FNov 9Nov 19Nov 26Dec 1Dec 7Dec 13Dec 20Dec 30Jan 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°F166159154151147143138132124
32°F200190183178174170166161154
28°F238229222215209202197189180
24°F282268261254248241234226215
20°F326312303293284275267259248
16°F353338329320312305296283270

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
96% 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
5,340
Cooling degree days, base 65°F
636
Growing degree days, base 40°F
5,098
Growing degree days, base 45°F
3,791
Growing degree days, base 50°F
2,715
Growing degree days, base 55°F
1,845
Growing degree days, base 60°F
1,155

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January93503
February75604
March640018
April449172
May23820256
June8773437
July9255711
August12223676
September10762407
October4233114
November729015
December95604

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 14.2 km from Umatilla County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00024155 (Pendleton). Public domain.