Frost Dates for 97222 — Milwaukie, Oregon

Half of springs at Oregon City, OR see their last 32°F night by March 18; only one in ten is past it by February 19, and one in ten still has one after April 11. Planting tender crops after March 27 leaves a 30% risk of a frost on them, after April 1 20%, and after April 11 10%. The 24 days between the even-odds date and the one-in-ten date is wider than at 60% of the 103 Oregon stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by November 18 in half of years, as early as October 30 one year in ten, and holds off past December 12 one year in ten. A hard freeze of 28°F follows 20 days later, around December 8; in spring the one-in-ten date for 28°F is March 7, 35 days before the 32°F one. The freeze-free season lasts 244 days in a typical year, longer than at 81% of the 103 Oregon stations; it reaches 280 days one year in ten and falls short of 214 one year in ten. On average 30 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 28 days longer, to about April 15, and return around October 31. Nights of 24°F, cold enough to damage hardier plants, come in 69% of winters and 16°F in 8%.

August is the warmest month at Oregon City, OR, averaging 84°F by day and 58°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 January (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 90% of years and March still brings one in 69% of years and April still brings one in 22% of years.

Warmth for growing adds up to 2,908 growing degree days a year (base 50°F), more than at 87% of the 103 Oregon stations. 32% of them (937) have built up by the end of June, and August adds the most, 645. Precipitation totals 44.7 inches a year, most in December (7.2") and least in July (0.5"); May to September bring 16% of it.

The nearest other station, Portland Kgw-Tv, OR, 6 miles northwest of Milwaukie, has a last frost 21 days earlier (February 25), a first frost 13 days later (December 1), a season 36 days longer.

Measurable snow is rare here: only 8 of 27 winters from 1991 to 2020 recorded 0.1 inch or more at Oregon City, OR, 6 miles away, so there is no typical first-snow date to plan around.

ZIP 97222 is 6 miles from Oregon City, OR, which stands at 167 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 8 other ZIP codes share the station; its figures are presented in full for 97045 (Oregon City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 97222 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.