Frost Dates for 15122 — West Mifflin, Pennsylvania

Half of springs at Pittsburgh Allegheny Co Airport, PA see their last 32°F night by April 18; only one in ten is past it by April 2, and one in ten still has one after May 6. Planting tender crops after April 24 leaves a 30% risk of a frost on them, after April 28 20%, and after May 6 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 70% of the 176 Pennsylvania stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 28 in half of years, as early as October 14 one year in ten, and holds off past November 10 one year in ten. A hard freeze of 28°F follows 11 days later, around November 8; in spring the one-in-ten date for 28°F is April 21, 15 days before the 32°F one. The freeze-free season lasts 193 days in a typical year, longer than at 85% of the 176 Pennsylvania stations; it reaches 212 days one year in ten and falls short of 171 one year in ten. On average 106 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 11 days longer, to about April 29, and return around October 17. Severe cold of 16°F or below comes every winter, usually between December 16 and March 8.

July is the warmest month at Pittsburgh Allegheny Co Airport, PA, averaging 83°F by day and 64°F at night; January is the coldest at 37°F and 22°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 17% of years.

Warmth for growing adds up to 3,286 growing degree days a year (base 50°F), more than at 79% of the 176 Pennsylvania stations. 36% of them (1,175) have built up by the end of June, and July adds the most, 730. Precipitation totals 41.3 inches a year, most in June (4.6") and least in February (2.6"); May to September bring 48% of it.

The nearest other station, Braddock Lock 2, PA, 3 miles northeast of West Mifflin and 518 feet lower, has a last frost 13 days earlier (April 5), a first frost 13 days later (November 10), a season 26 days longer.

The first measurable snow (0.1 inch or more) in West Mifflin usually arrives around December 22, and the last of the season around February 22. Those are the middle dates across the winters of 1991–2020 at Braddock Lock 2, PA, 2.5 miles away: half of years saw snow earlier, half later. Snow fell in 81% of those winters. The last 32°F night of spring typically comes 55 days after the last snow.

ZIP 15122 is 2 miles from Pittsburgh Allegheny Co Airport, PA, which stands at 1,248 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 16 other ZIP codes share the station; its figures are presented in full for 15236 (Pittsburgh). The 2023 USDA Plant Hardiness Zone Map lists ZIP 15122 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.