Frost Dates for 97882 — Umatilla, Oregon

Half of springs at Mcnary Dam #2, OR see their last 32°F night by March 30; only one in ten is past it by March 12, and one in ten still has one after April 20. Planting tender crops after April 4 leaves a 30% risk of a frost on them, after April 11 20%, and after April 20 10%. The 21 days between the even-odds date and the one-in-ten date is narrower than at 55% of the 103 Oregon stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by November 4 in half of years, as early as October 21 one year in ten, and holds off past November 19 one year in ten. A hard freeze of 28°F follows 10 days later, around November 14; in spring the one-in-ten date for 28°F is March 30, 21 days before the 32°F one. The freeze-free season lasts 217 days in a typical year, longer than at 61% of the 103 Oregon stations; it reaches 240 days one year in ten and falls short of 194 one year in ten. On average 74 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 21 days longer, to about April 20, and return around October 24. Nights of 24°F, cold enough to damage hardier plants, come in 100% of winters and 16°F in 79%.

July is the warmest month at Mcnary Dam #2, OR, averaging 89°F by day and 61°F at night; January is the coldest at 41°F and 30°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 40% of years.

Warmth for growing adds up to 3,096 growing degree days a year (base 50°F), more than at 93% of the 103 Oregon stations. 30% of them (932) have built up by the end of June, and July adds the most, 759. Precipitation totals 8.1 inches a year, most in December (1.2") and least in July (0.2"); May to September bring 27% of it.

The nearest other station, Hermiston 2 NW, OR, 4 miles south of Umatilla, has a last frost 28 days later (April 27), a first frost 28 days earlier (October 7), a season 54 days shorter.

The first measurable snow (0.1 inch or more) in Umatilla 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, 27.8 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 29 days after the last snow.

ZIP 97882 is 2 miles from Mcnary Dam #2, OR, which stands at 361 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 97882 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.