Frost Dates for 99301 — Pasco, Washington

Half of springs at Pasco Tri Cities Airport, WA see their last 32°F night by April 27; only one in ten is past it by April 8, and one in ten still has one after May 10. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 6 20%, and after May 10 10%. The 13 days between the even-odds date and the one-in-ten date is the narrowest 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 28 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 April 28, 12 days before the 32°F one. The freeze-free season lasts 168 days in a typical year, shorter than at 71% of the 113 Washington stations; it reaches 189 days one year in ten and falls short of 148 one year in ten. On average 112 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 12 days longer, to about May 9, and return around September 29. Severe cold of 16°F or below comes in 98% of winters, usually between December 4 and February 11.

July is the warmest month at Pasco Tri Cities Airport, WA, averaging 93°F by day and 57°F at night; December is the coldest at 41°F and 27°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 3,103 growing degree days a year (base 50°F), more than at 92% of the 113 Washington stations. 34% of them (1,042) have built up by the end of June, and July adds the most, 765. Precipitation totals 7.7 inches a year, most in January (1.0") and least in July (0.2"); May to September bring 27% of it.

The nearest other station, Kennewick, WA, 4 miles south of Pasco, has a last frost 30 days earlier (March 28), a first frost 19 days later (October 30), a season 48 days longer.

Measurable snow is rare here: only 9 of 21 winters from 1991 to 2020 recorded 0.1 inch or more at Ice Harbor Dam, WA, 10.5 miles away, so there is no typical first-snow date to plan around.

ZIP 99301 is 1 mile from Pasco Tri Cities Airport, WA, which stands at 407 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99301 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.