Frost Dates for 17103 — Harrisburg, Pennsylvania

Half of springs at Harrisburg 1 NE, PA see their last 32°F night by April 15; only one in ten is past it by April 1, and one in ten still has one after May 2. Planting tender crops after April 21 leaves a 30% risk of a frost on them, after April 26 20%, and after May 2 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 50% of the 176 Pennsylvania stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 23 in half of years, as early as October 7 one year in ten, and holds off past November 7 one year in ten. A hard freeze of 28°F follows 13 days later, around November 5; in spring the one-in-ten date for 28°F is April 16, 16 days before the 32°F one. The freeze-free season lasts 189 days in a typical year, longer than at 78% of the 176 Pennsylvania stations; it reaches 210 days one year in ten and falls short of 167 one year in ten. On average 111 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 15 days longer, to about April 30, and return around October 12. Severe cold of 16°F or below comes every winter, usually between December 20 and March 3.

July is the warmest month at Harrisburg 1 NE, PA, averaging 85°F by day and 65°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 13% of years.

Warmth for growing adds up to 3,209 growing degree days a year (base 50°F), more than at 70% of the 176 Pennsylvania stations. 34% of them (1,102) have built up by the end of June, and July adds the most, 773. Precipitation totals 45.3 inches a year, most in July (4.8") and least in February (2.8"); May to September bring 48% of it.

The nearest other station, Harrisburg Cptl Cy Airport, PA, 4 miles south of Harrisburg, has a last frost 6 days earlier (April 9), a first frost 9 days later (November 1), a season 16 days longer.

The first measurable snow (0.1 inch or more) in Harrisburg usually arrives around December 9, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Harrisburg 1 NE, PA, 0.7 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 29 days after the last snow.

ZIP 17103 is under a mile from Harrisburg 1 NE, PA, which stands at 420 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 13 other ZIP codes share the station; its figures are presented in full for 17050 (Mechanicsburg). The 2023 USDA Plant Hardiness Zone Map lists ZIP 17103 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.