Frost Dates for 15033 — Donora, Pennsylvania

Half of springs at Donora 1 SW, PA see their last 32°F night by April 27; only one in ten is past it by April 11, and one in ten still has one after May 15. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 8 20%, and after May 15 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 22 in half of years, as early as October 8 one year in ten, and holds off past November 4 one year in ten. A hard freeze of 28°F follows 10 days later, around November 1; in spring the one-in-ten date for 28°F is May 4, 11 days before the 32°F one. The freeze-free season lasts 177 days in a typical year, longer than at 56% of the 176 Pennsylvania stations; it reaches 198 days one year in ten and falls short of 156 one year in ten. On average 116 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 9 days longer, to about May 6, and return around October 12. Severe cold of 16°F or below comes every winter, usually between December 11 and March 9.

July is the warmest month at Donora 1 SW, PA, averaging 84°F by day and 62°F at night; January is the coldest at 39°F and 21°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 38% of years.

Warmth for growing adds up to 3,212 growing degree days a year (base 50°F), more than at 71% of the 176 Pennsylvania stations. 35% of them (1,110) have built up by the end of June, and July adds the most, 722. Precipitation totals 40.8 inches a year, most in June (4.4") and least in February (2.4"); May to September bring 50% of it.

The nearest other station, Charleroi Lock 4, PA, 3 miles southwest of Donora, has a last frost 14 days earlier (April 13), a first frost 14 days later (November 5), a season 28 days longer.

The first measurable snow (0.1 inch or more) in Donora usually arrives around December 12, and the last of the season around March 12. Those are the middle dates across the winters of 1991–2020 at Donora 1 SW, PA, 1 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 46 days after the last snow.

ZIP 15033 is 1 mile from Donora 1 SW, PA, which stands at 762 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 5 other ZIP codes share the station; its figures are presented in full for 15012 (Belle Vernon). The 2023 USDA Plant Hardiness Zone Map lists ZIP 15033 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.