Forest Grove climate

Forest Grove Frost Dates and Growing Season

NOAA 1991-2020 normals for Forest Grove, 0.8 km from Forest Grove, elevation 180 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Forest Grove. 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 16 and the first fall freeze around October 26, a growing season of about 192 days.

Median at 36°F
last May 4, first October 8
Median at 32°F
last April 16, first October 26
Median at 28°F
last March 19, first November 11

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 25May 17May 12May 7May 4May 1Apr 29Apr 26Apr 19
32°FMay 5Apr 30Apr 26Apr 20Apr 16Apr 11Apr 6Apr 1Mar 26
28°FApr 12Apr 3Mar 30Mar 24Mar 19Mar 13Mar 6Feb 28Feb 21
24°FMar 16Mar 3Feb 28Feb 23Feb 17Feb 11Feb 1Jan 21Jan 5
20°FFeb 23Feb 16Feb 6Jan 30Jan 18Jan 7Jan 1Dec 19Dec 8
16°FFeb 13Feb 4Jan 24Jan 10Jan 2Dec 27Dec 17Dec 10Dec 2

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 24Sep 30Oct 2Oct 5Oct 8Oct 13Oct 16Oct 21Oct 30
32°FOct 6Oct 13Oct 18Oct 22Oct 26Oct 30Nov 3Nov 7Nov 14
28°FOct 23Oct 29Nov 2Nov 7Nov 11Nov 16Nov 21Nov 27Dec 5
24°FNov 6Nov 13Nov 19Nov 25Nov 30Dec 5Dec 11Dec 19Jan 1
20°FNov 16Nov 27Dec 2Dec 8Dec 15Dec 22Dec 29Jan 6Jan 25
16°FNov 26Dec 3Dec 8Dec 13Dec 22Dec 28Jan 5Jan 21Feb 7

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°F183173167160155151145139131
32°F222212204198192186181174165
28°F272259251243236230223213201
24°F331318306298287278270261248
20°F365361351341333325316307291
16°F365365365365364355342332321

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
99% of years
20°F or colder
85% of years
16°F or colder
48% 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
5,027
Cooling degree days, base 65°F
347
Growing degree days, base 40°F
4,727
Growing degree days, base 45°F
3,348
Growing degree days, base 50°F
2,256
Growing degree days, base 55°F
1,408
Growing degree days, base 60°F
775

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January81201
February66502
March612017
April461166
May27316222
June14739343
July42122546
August35123553
September12345373
October3912119
November642012
December82502

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 0.8 km from Forest Grove. 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 USC00352997 (Forest Grove). Public domain.