Frost Dates for 97836 — Heppner, Oregon

Half of springs at Heppner, OR see their last 32°F night by April 26; only one in ten is past it by April 6, and one in ten still has one after May 11. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 5 20%, and after May 11 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 95% of the 103 Oregon stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 19 in half of years, as early as October 3 one year in ten, and holds off past November 2 one year in ten. A hard freeze of 28°F follows 13 days later, around November 1; in spring the one-in-ten date for 28°F is April 24, 17 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, shorter than at 67% of the 103 Oregon stations; it reaches 199 days one year in ten and falls short of 150 one year in ten. On average 106 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 16 days longer, to about May 12, and return around October 5. Severe cold of 16°F or below comes in 97% of winters, usually between December 7 and February 7.

July is the warmest month at Heppner, OR, averaging 87°F by day and 55°F at night; December is the coldest at 43°F and 27°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 31% of years.

Warmth for growing adds up to 2,521 growing degree days a year (base 50°F), more than at 71% of the 103 Oregon stations. 28% of them (717) have built up by the end of June, and July adds the most, 649. Precipitation totals 13.3 inches a year, most in May (1.7") and least in July (0.3"); May to September bring 31% of it.

The nearest other station, Boardman, OR, 36 miles north of Heppner and 1,605 feet lower, has a last frost 12 days earlier (April 14), a first frost 2 days later (October 21), a season 14 days longer.

The first measurable snow (0.1 inch or more) in Heppner usually arrives around December 6, and the last of the season around February 20. Those are the middle dates across the winters of 1991–2020 at Heppner, OR, 1.9 miles away: half of years saw snow earlier, half later. Snow fell in 97% of those winters. The last 32°F night of spring typically comes 65 days after the last snow.

ZIP 97836 is 2 miles from Heppner, OR, which stands at 1,885 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97836 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.