Frost Dates for 97850 — La Grande, Oregon

Half of springs at La Grande, OR see their last 32°F night by May 6; only one in ten is past it by April 21, and one in ten still has one after May 26. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 17 20%, and after May 26 10%. The 20 days between the even-odds date and the one-in-ten date is narrower than at 64% of the 103 Oregon stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 1 in half of years, as early as September 17 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 13 days later, around October 14; in spring the one-in-ten date for 28°F is May 5, 21 days before the 32°F one. The freeze-free season lasts 146 days in a typical year, shorter than at 80% of the 103 Oregon stations; it reaches 168 days one year in ten and falls short of 123 one year in ten. On average 136 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 20 days longer, to about May 26, and return around September 19. Severe cold of 16°F or below comes every winter, usually between November 28 and February 17.

July is the warmest month at La Grande, OR, averaging 86°F by day and 55°F at night; December is the coldest at 39°F and 24°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 68% of years.

Warmth for growing adds up to 2,278 growing degree days a year (base 50°F), more than at 53% of the 103 Oregon stations. 27% of them (607) have built up by the end of June, and July adds the most, 631. Precipitation totals 17.4 inches a year, most in May (2.2") and least in July (0.6"); May to September bring 32% of it.

The nearest other station, Union, OR, 14 miles southeast of La Grande, has a last frost 5 days later (May 11), a first frost 5 days earlier (September 26), a season 10 days shorter.

The first measurable snow (0.1 inch or more) in La Grande usually arrives around November 29, and the last of the season around March 11. Those are the middle dates across the winters of 1991–2020 at La Grande, OR, 0.7 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 56 days after the last snow.

ZIP 97850 is under a mile from La Grande, OR, which stands at 2,755 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97850 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.