Frost Dates for 97218 — Portland, Oregon

Half of springs at Portland International Airport, OR see their last 32°F night by March 13; only one in ten is past it by February 22, and one in ten still has one after April 1. Planting tender crops after March 21 leaves a 30% risk of a frost on them, after March 26 20%, and after April 1 10%. The 19 days between the even-odds date and the one-in-ten date is narrower than at 70% of the 103 Oregon stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 19 in half of years, as early as October 29 one year in ten, and holds off past December 10 one year in ten. A hard freeze of 28°F follows 16 days later, around December 5; in spring the one-in-ten date for 28°F is March 6, 26 days before the 32°F one. The freeze-free season lasts 247 days in a typical year, longer than at 83% of the 103 Oregon stations; it reaches 277 days one year in ten and falls short of 219 one year in ten. On average 32 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 24 days longer, to about April 6, and return around November 2. Nights of 24°F, cold enough to damage hardier plants, come in 69% of winters and 16°F in 11%.

August is the warmest month at Portland International Airport, OR, averaging 82°F by day and 59°F at night; December is the coldest at 47°F and 36°F. A freezing night is all but certain in every month from December to February (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, March still brings one in 76% of years and April still brings one in 11% of years.

Warmth for growing adds up to 2,832 growing degree days a year (base 50°F), more than at 85% of the 103 Oregon stations. 31% of them (881) have built up by the end of June, and August adds the most, 639. Precipitation totals 36.9 inches a year, most in December (5.8") and least in July (0.5"); May to September bring 18% of it.

The nearest other station, Portland WFO, OR, 3 miles east of Portland, has the same 50% last-frost date, a first frost 3 days later (November 22), a season 4 days longer.

The first measurable snow (0.1 inch or more) in Portland usually arrives around December 24, and the last of the season around February 8. Those are the middle dates across the winters of 1991–2020 at Portland International Airport, OR, 2.1 miles away: half of years saw snow earlier, half later. Snow fell in 77% of those winters. The last 32°F night of spring typically comes 33 days after the last snow.

ZIP 97218 is 2 miles from Portland International Airport, OR, which stands at 19 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 98684 (Vancouver). The 2023 USDA Plant Hardiness Zone Map lists ZIP 97218 in zone 9a, the band where the coldest night of the year averaged 20 to 25°F (-6.7 to -3.9°C) over 1991–2020; a zone describes winter lows, not frost dates.