Frost Dates for 98813 — Bridgeport, Washington

Half of springs at Chief Joseph Dam, WA see their last 32°F night by April 26; only one in ten is past it by April 9, and one in ten still has one after May 13. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 7 20%, and after May 13 10%. The 17 days between the even-odds date and the one-in-ten date is narrower than at 66% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 11 in half of years, as early as September 30 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 12 days later, around October 23; in spring the one-in-ten date for 28°F is May 2, 11 days before the 32°F one. The freeze-free season lasts 167 days in a typical year, shorter than at 74% of the 113 Washington stations; it reaches 190 days one year in ten and falls short of 147 one year in ten. On average 128 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 10, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 27 and February 19.

July is the warmest month at Chief Joseph Dam, WA, averaging 91°F by day and 58°F at night; January is the coldest at 34°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 35% of years.

Warmth for growing adds up to 2,942 growing degree days a year (base 50°F), more than at 88% of the 113 Washington stations. 31% of them (899) have built up by the end of June, and July adds the most, 762. Precipitation totals 10.9 inches a year, most in December (2.0") and least in August (0.2"); May to September bring 26% of it.

The nearest other station, Chelan, WA, 19 miles southwest of Bridgeport and 360 feet higher, has a last frost 9 days earlier (April 17), a first frost 11 days later (October 22), a season 20 days longer.

The first measurable snow (0.1 inch or more) in Bridgeport usually arrives around November 28, and the last of the season around February 22. Those are the middle dates across the winters of 1991–2020 at Chief Joseph Dam, WA, 0.6 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 63 days after the last snow.

ZIP 98813 is under a mile from Chief Joseph Dam, WA, which stands at 834 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 98812 (Brewster). The 2023 USDA Plant Hardiness Zone Map lists ZIP 98813 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.