Morrow County climate

Morrow County Frost Dates and Growing Season

NOAA 1991-2020 normals for Heppner, 6.2 km from Morrow County, elevation 1885 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Heppner. 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 19, a growing season of about 174 days.

Median at 36°F
last May 12, first October 5
Median at 32°F
last April 26, first October 19
Median at 28°F
last April 2, first November 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°FJun 1May 24May 19May 15May 12May 9May 6May 2Apr 28
32°FMay 11May 5May 1Apr 29Apr 26Apr 23Apr 18Apr 14Apr 6
28°FApr 24Apr 17Apr 12Apr 6Apr 2Mar 30Mar 25Mar 17Mar 9
24°FApr 5Mar 29Mar 21Mar 14Mar 8Mar 3Feb 28Feb 23Feb 15
20°FMar 17Mar 6Mar 1Feb 25Feb 20Feb 16Feb 10Feb 3Jan 21
16°FMar 3Feb 27Feb 20Feb 14Feb 7Feb 1Jan 24Jan 13Jan 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 22Sep 27Sep 30Oct 3Oct 5Oct 8Oct 12Oct 15Oct 20
32°FOct 3Oct 8Oct 12Oct 15Oct 19Oct 22Oct 26Oct 29Nov 2
28°FOct 15Oct 21Oct 26Oct 29Nov 1Nov 4Nov 9Nov 14Nov 20
24°FOct 26Oct 31Nov 4Nov 9Nov 15Nov 19Nov 23Nov 26Dec 2
20°FNov 1Nov 11Nov 17Nov 22Nov 26Nov 30Dec 5Dec 11Dec 19
16°FNov 11Nov 21Nov 27Dec 2Dec 7Dec 13Dec 20Dec 30Jan 14

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°F163156151147142138133127118
32°F199190184179174169164158150
28°F239230222216210205199193183
24°F277268259250245238233225214
20°F318302292284277271263254242
16°F348334323314306298289280266

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
97% 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
5,380
Cooling degree days, base 65°F
531
Growing degree days, base 40°F
4,902
Growing degree days, base 45°F
3,588
Growing degree days, base 50°F
2,521
Growing degree days, base 55°F
1,672
Growing degree days, base 60°F
1,013

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January91102
February74805
March646019
April472166
May26818232
June11758392
July23207649
August20187632
September12357387
October4173116
November702017
December93503

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 6.2 km from Morrow 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 USC00353827 (Heppner). Public domain.