Union County climate

Union County Frost Dates and Growing Season

NOAA 1991-2020 normals for La Grande, 5.2 km from Union County, elevation 2755 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for La Grande. 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 May 6 and the first fall freeze around October 1, a growing season of about 146 days.

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

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 3Sep 8Sep 13Sep 16Sep 19Sep 22Sep 25Sep 29Oct 3
32°FSep 17Sep 22Sep 27Sep 30Oct 1Oct 4Oct 7Oct 11Oct 16
28°FSep 30Oct 3Oct 7Oct 10Oct 14Oct 17Oct 20Oct 24Oct 29
24°FOct 12Oct 19Oct 22Oct 26Oct 29Nov 1Nov 5Nov 12Nov 21
20°FOct 24Oct 29Nov 3Nov 10Nov 15Nov 20Nov 23Nov 28Dec 4
16°FNov 1Nov 11Nov 19Nov 24Nov 28Dec 2Dec 6Dec 12Dec 21

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°F1391321261211161121069990
32°F168161156151146142137131123
28°F201192186181177172167163155
24°F243234227219213208202195187
20°F284272265259253247241233222
16°F318306298291284277270262253

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
6,132
Cooling degree days, base 65°F
477
Growing degree days, base 40°F
4,354
Growing degree days, base 45°F
3,212
Growing degree days, base 50°F
2,278
Growing degree days, base 55°F
1,519
Growing degree days, base 60°F
916

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02500
February82900
March74108
April542047
May31510194
June14549358
July27193631
August30181617
September16243339
October496078
November78506
December1,03700

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 5.2 km from Union 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 USC00354622 (La Grande). Public domain.