Frost Dates for 19111 — Philadelphia, Pennsylvania

Half of springs at Philadelphia NE Airport, PA see their last 32°F night by April 4; only one in ten is past it by March 21, and one in ten still has one after April 17. Planting tender crops after April 9 leaves a 30% risk of a frost on them, after April 13 20%, and after April 17 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 94% of the 176 Pennsylvania stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 7 in half of years, as early as October 24 one year in ten, and holds off past November 22 one year in ten. A hard freeze of 28°F follows 12 days later, around November 19; in spring the one-in-ten date for 28°F is April 5, 12 days before the 32°F one. The freeze-free season lasts 216 days in a typical year, longer than at 97% of the 176 Pennsylvania stations; it reaches 236 days one year in ten and falls short of 197 one year in ten. On average 88 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 13 days longer, to about April 17, and return around October 27. Severe cold of 16°F or below comes in 97% of winters, usually between January 3 and February 14.

July is the warmest month at Philadelphia NE Airport, PA, averaging 88°F by day and 69°F at night; January is the coldest at 42°F and 27°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 63% of years.

Warmth for growing adds up to 4,064 growing degree days a year (base 50°F), more than at 99% of the 176 Pennsylvania stations. 34% of them (1,397) have built up by the end of June, and July adds the most, 893. Precipitation totals 45.0 inches a year, most in September (4.5") and least in February (2.6"); May to September bring 46% of it.

The nearest other station, Pennsauken 1N, NJ, 7 miles southeast of Philadelphia, has a last frost 11 days later (April 15), a first frost 7 days earlier (October 31), a season 17 days shorter.

The first measurable snow (0.1 inch or more) in Philadelphia usually arrives around January 10, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Pennsauken 1N, NJ, 7 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 26 days after the last snow.

ZIP 19111 is 4 miles from Philadelphia NE Airport, PA, which stands at 100 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 14 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 19111 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.