Portland climate

Portland Frost Dates and Growing Season

NOAA 1991-2020 normals for Corpus Christi NWS, 20.9 km from Portland, elevation 44 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Corpus Christi NWS. 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 January 31 and the first fall freeze around December 22, a growing season of about 331 days.

Median at 36°F
last February 18, first December 7
Median at 32°F
last January 31, first December 22
Median at 28°F
last January 11, first January 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°FMar 12Mar 4Mar 1Feb 24Feb 18Feb 12Feb 6Jan 29Jan 18
32°FMar 2Feb 21Feb 12Feb 5Jan 31Jan 24Jan 15Jan 5Dec 24
28°FFeb 17Feb 5Jan 30Jan 21Jan 11Jan 5Dec 31Dec 23Dec 13
24°FFeb 9Jan 30Jan 12Jan 8Jan 5Jan 1Dec 29Dec 21Dec 12
20°F–––––––––
16°F–––––––––

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°FNov 16Nov 24Nov 29Dec 2Dec 7Dec 11Dec 17Dec 24Jan 4
32°FNov 29Dec 5Dec 10Dec 16Dec 22Dec 28Jan 4Jan 13Feb 1
28°FDec 7Dec 14Dec 21Dec 27Jan 1Jan 5Jan 11Jan 23Feb 4
24°FDec 11Dec 21Dec 26Dec 31Jan 1Jan 6Jan 10Jan 24Feb 4
20°F–––––––––
16°F–––––––––

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°F333319311304297289280271262
32°F365355343338331323313305291
28°F365365365365364355345337324
24°F365365365365365365365365352
20°F365365365365365365365365365
16°F365365365365365365365365365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
99% of years
32°F or colder
88% of years
28°F or colder
52% of years
24°F or colder
15% of years
20°F or colder
1% of years
16°F or colder
0% 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
942
Cooling degree days, base 65°F
3,510
Growing degree days, base 40°F
11,705
Growing degree days, base 45°F
9,907
Growing degree days, base 50°F
8,154
Growing degree days, base 55°F
6,481
Growing degree days, base 60°F
4,927

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January30127238
February17851315
March86118502
April16224659
May1408873
June0528978
July05951,060
August06111,076
September0476926
October11311766
November104117471
December24744292

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 20.9 km from Portland. 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 USC00412011 (Corpus Christi NWS). Public domain.