Umatilla climate

Umatilla Frost Dates and Growing Season

NOAA 1991-2020 normals for Mcnary Dam #2, 3.9 km from Umatilla, elevation 361 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mcnary Dam #2. 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 March 30 and the first fall freeze around November 4, a growing season of about 217 days.

Median at 36°F
last April 20, first October 24
Median at 32°F
last March 30, first November 4
Median at 28°F
last March 11, first November 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°FMay 7May 2Apr 28Apr 24Apr 20Apr 16Apr 12Apr 8Apr 2
32°FApr 20Apr 11Apr 4Apr 1Mar 30Mar 27Mar 24Mar 19Mar 12
28°FMar 30Mar 25Mar 20Mar 15Mar 11Mar 7Mar 3Feb 27Feb 19
24°FMar 13Mar 5Feb 28Feb 25Feb 20Feb 16Feb 9Feb 2Jan 17
20°FFeb 28Feb 23Feb 17Feb 10Feb 5Jan 29Jan 18Jan 8Dec 30
16°FFeb 22Feb 15Feb 6Feb 1Jan 24Jan 15Jan 7Dec 28Dec 12

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°FOct 9Oct 15Oct 18Oct 21Oct 24Oct 27Oct 29Nov 1Nov 6
32°FOct 21Oct 26Oct 29Nov 1Nov 4Nov 6Nov 10Nov 13Nov 19
28°FOct 28Nov 3Nov 7Nov 11Nov 14Nov 18Nov 22Nov 26Dec 3
24°FNov 6Nov 12Nov 19Nov 23Nov 27Dec 1Dec 8Dec 15Dec 28
20°FNov 13Nov 24Nov 30Dec 5Dec 11Dec 17Dec 26Jan 4Jan 22
16°FNov 24Dec 3Dec 8Dec 15Dec 23Dec 31Jan 7Jan 19Feb 6

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°F208200195190185181175169163
32°F240231226221217213208202194
28°F279267258253247242237230223
24°F320307296288281273265257247
20°F349335328320312305297287269
16°F365363350342334329320310297

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
95% of years
16°F or colder
79% 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
4,821
Cooling degree days, base 65°F
788
Growing degree days, base 40°F
5,607
Growing degree days, base 45°F
4,243
Growing degree days, base 50°F
3,096
Growing degree days, base 55°F
2,155
Growing degree days, base 60°F
1,385

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January91301
February72903
March609015
April3851100
May17520311
June47100503
July2296759
August2288752
September5980471
October3394161
November662018
December90004

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 3.9 km from Umatilla. 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 USC00355392 (Mcnary Dam #2). Public domain.