Frost Dates for 99352 — Richland, Washington

Half of springs at Richland, WA see their last 32°F night by April 6; only one in ten is past it by March 22, and one in ten still has one after April 24. Planting tender crops after April 13 leaves a 30% risk of a frost on them, after April 17 20%, and after April 24 10%. The 18 days between the even-odds date and the one-in-ten date is narrower than at 56% of the 113 Washington stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 24 in half of years, as early as October 10 one year in ten, and holds off past November 8 one year in ten. A hard freeze of 28°F follows 11 days later, around November 4; in spring the one-in-ten date for 28°F is April 5, 19 days before the 32°F one. The freeze-free season lasts 200 days in a typical year, longer than at 58% of the 113 Washington stations; it reaches 221 days one year in ten and falls short of 179 one year in ten. On average 91 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 19 days longer, to about April 25, and return around October 14. Nights of 24°F, cold enough to damage hardier plants, come in 100% of winters and 16°F in 89%.

July is the warmest month at Richland, WA, averaging 89°F by day and 60°F at night; December is the coldest at 40°F and 28°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 67% of years.

Warmth for growing adds up to 3,125 growing degree days a year (base 50°F), more than at 93% of the 113 Washington stations. 33% of them (1,018) have built up by the end of June, and July adds the most, 764. Precipitation totals 7.2 inches a year, most in December (1.1") and least in August (0.1"); May to September bring 25% of it.

The nearest other station, Pasco Tri Cities Airport, WA, 8 miles east of Richland, has a last frost 21 days later (April 27), a first frost 13 days earlier (October 11), a season 32 days shorter.

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, 19.4 miles away, so there is no typical first-snow date to plan around.

ZIP 99352 is 2 miles from Richland, WA, which stands at 373 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99352 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.