Hermiston climate

Hermiston Frost Dates and Growing Season

NOAA 1991-2020 normals for Hermiston Muni AP, 2.7 km from Hermiston, elevation 641 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hermiston Muni AP. 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 10, a growing season of about 167 days.

Median at 36°F
last May 8, first September 28
Median at 32°F
last April 26, first October 10
Median at 28°F
last April 9, first October 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°FMay 22May 17May 14May 11May 8May 6May 3Apr 30Apr 26
32°FMay 10May 6May 2Apr 29Apr 26Apr 23Apr 20Apr 15Apr 9
28°FApr 29Apr 21Apr 17Apr 13Apr 9Apr 5Apr 1Mar 28Mar 20
24°FApr 11Apr 2Mar 28Mar 24Mar 18Mar 13Mar 8Mar 4Feb 25
20°FMar 21Mar 12Mar 6Mar 2Feb 28Feb 23Feb 17Feb 11Jan 28
16°FMar 5Feb 28Feb 24Feb 18Feb 12Feb 5Jan 28Jan 14Jan 1

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 12Sep 19Sep 22Sep 26Sep 28Oct 1Oct 4Oct 7Oct 12
32°FSep 25Oct 1Oct 3Oct 7Oct 10Oct 14Oct 17Oct 22Oct 26
28°FOct 4Oct 10Oct 15Oct 20Oct 24Oct 27Oct 29Nov 2Nov 7
24°FOct 17Oct 23Oct 28Nov 1Nov 3Nov 7Nov 12Nov 19Nov 28
20°FOct 26Nov 1Nov 7Nov 12Nov 18Nov 24Nov 30Dec 8Dec 18
16°FNov 3Nov 12Nov 21Nov 27Dec 5Dec 10Dec 19Dec 31Jan 17

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°F160155149145142137133128122
32°F190182176171167163158153143
28°F224214208203196191187181169
24°F263251242235229223217209198
20°F306294282274266259252243231
16°F342328318307299291281270257

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
4,859
Cooling degree days, base 65°F
841
Growing degree days, base 40°F
5,675
Growing degree days, base 45°F
4,325
Growing degree days, base 50°F
3,173
Growing degree days, base 55°F
2,220
Growing degree days, base 60°F
1,443

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January89902
February72005
March577032
April3692116
May15539350
June38116528
July3333795
August6281741
September8168437
October3833141
November705020
December92505

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 2.7 km from Hermiston. 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 USW00004113 (Hermiston Muni AP). Public domain.