Frost Dates for 97124 — Hillsboro, Oregon

Half of springs at Portland-Hillsboro Airport, OR see their last 32°F night by April 16; only one in ten is past it by March 25, and one in ten still has one after May 3. Planting tender crops after April 25 leaves a 30% risk of a frost on them, after April 29 20%, and after May 3 10%. The 17 days between the even-odds date and the one-in-ten date is narrower than at 83% of the 103 Oregon stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 23 in half of years, as early as October 3 one year in ten, and holds off past November 18 one year in ten. A hard freeze of 28°F follows 20 days later, around November 12; in spring the one-in-ten date for 28°F is April 9, 24 days before the 32°F one. The freeze-free season lasts 191 days in a typical year, shorter than at 56% of the 103 Oregon stations; it reaches 223 days one year in ten and falls short of 161 one year in ten. On average 64 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 19 days longer, to about May 5, and return around October 6. Nights of 24°F, cold enough to damage hardier plants, come in 98% of winters and 16°F in 29%.

July is the warmest month at Portland-Hillsboro Airport, OR, averaging 82°F by day and 52°F at night; December is the coldest at 46°F and 33°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 73% of years and May still brings one in 16% of years.

Warmth for growing adds up to 2,195 growing degree days a year (base 50°F), fewer than at 54% of the 103 Oregon stations. 29% of them (640) have built up by the end of June, and July adds the most, 532. Precipitation totals 36.1 inches a year, most in December (6.1") and least in July (0.4"); May to September bring 16% of it.

The nearest other station, Nature Park-Beaverton, OR, 6 miles southeast of Hillsboro, has a last frost 64 days earlier (February 11), a first frost 43 days later (December 5), a season 112 days longer.

Measurable snow is rare here: only 10 of 29 winters from 1991 to 2020 recorded 0.1 inch or more at Forest Grove, OR, 7.7 miles away, so there is no typical first-snow date to plan around.

ZIP 97124 is under a mile from Portland-Hillsboro Airport, OR, which stands at 204 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97124 in zone 8b, the band where the coldest night of the year averaged 15 to 20°F (-9.4 to -6.7°C) over 1991–2020; a zone describes winter lows, not frost dates.