Frost Dates for 97838 — Hermiston, Oregon

Half of springs at Hermiston 2 NW, OR see their last 32°F night by April 27; only one in ten is past it by April 11, and one in ten still has one after May 11. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 6 20%, and after May 11 10%. The 14 days between the even-odds date and the one-in-ten date is the narrowest of the 103 Oregon stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 7 in half of years, as early as September 25 one year in ten, and holds off past October 21 one year in ten. A hard freeze of 28°F follows 13 days later, around October 20; in spring the one-in-ten date for 28°F is April 29, 12 days before the 32°F one. The freeze-free season lasts 163 days in a typical year, shorter than at 74% of the 103 Oregon stations; it reaches 183 days one year in ten and falls short of 143 one year in ten. On average 122 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 14 days longer, to about May 11, and return around September 26. Severe cold of 16°F or below comes in 99% of winters, usually between November 26 and February 18.

July is the warmest month at Hermiston 2 NW, OR, averaging 89°F by day and 56°F at night; December is the coldest at 42°F and 26°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 37% of years.

Warmth for growing adds up to 2,756 growing degree days a year (base 50°F), more than at 82% of the 103 Oregon stations. 32% of them (893) have built up by the end of June, and July adds the most, 705. Precipitation totals 8.9 inches a year, most in January (1.3") and least in July (0.2"); May to September bring 26% of it.

The nearest other station, Hermiston Municipal Airport, OR, 2 miles southeast of Hermiston and 181 feet higher, has a last frost 1 day earlier (April 26), a first frost 3 days later (October 10), a season 4 days longer.

The first measurable snow (0.1 inch or more) in Hermiston usually arrives around November 29, and the last of the season around March 1. Those are the middle dates across the winters of 1991–2020 at Pendleton, OR, 23.4 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 57 days after the last snow.

ZIP 97838 is 2 miles from Hermiston 2 NW, OR, which stands at 460 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97838 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.