Frost Dates for 97914 — Ontario, Oregon

Half of springs at Ontario Ksrv, OR see their last 32°F night by April 22; only one in ten is past it by April 7, and one in ten still has one after May 7. Planting tender crops after April 29 leaves a 30% risk of a frost on them, after May 2 20%, and after May 7 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 9 in half of years, as early as September 26 one year in ten, and holds off past October 23 one year in ten. A hard freeze of 28°F follows 12 days later, around October 21; in spring the one-in-ten date for 28°F is April 23, 14 days before the 32°F one. The freeze-free season lasts 168 days in a typical year, shorter than at 71% of the 103 Oregon stations; it reaches 187 days one year in ten and falls short of 149 one year in ten. On average 150 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 13 days longer, to about May 5, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 26 and February 10.

July is the warmest month at Ontario Ksrv, OR, averaging 93°F by day and 60°F at night; January is the coldest at 36°F and 23°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 25% of years.

Warmth for growing adds up to 3,072 growing degree days a year (base 50°F), more than at 92% of the 103 Oregon stations. 32% of them (972) have built up by the end of June, and July adds the most, 829. Precipitation totals 10.1 inches a year, most in December (1.6") and least in August (0.1"); May to September bring 28% of it.

The nearest other station, Payette, ID, 3 miles northeast of Ontario, has a last frost 3 days earlier (April 19), a first frost 11 days later (October 20), a season 15 days longer.

The first measurable snow (0.1 inch or more) in Ontario usually arrives around December 15, and the last of the season around February 4. Those are the middle dates across the winters of 1991–2020 at Payette, ID, 3.3 miles away: half of years saw snow earlier, half later. Snow fell in 95% of those winters. The last 32°F night of spring typically comes 77 days after the last snow.

ZIP 97914 is 1 mile from Ontario Ksrv, OR, which stands at 2,145 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 97914 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.