Frost Dates for 17027 — Grantham, Pennsylvania

Half of springs at Harrisburg Cptl Cy Airport, PA see their last 32°F night by April 9; only one in ten is past it by March 27, and one in ten still has one after April 25. Planting tender crops after April 16 leaves a 30% risk of a frost on them, after April 19 20%, and after April 25 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 51% of the 176 Pennsylvania stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 1 in half of years, as early as October 16 one year in ten, and holds off past November 15 one year in ten. A hard freeze of 28°F follows 11 days later, around November 12; in spring the one-in-ten date for 28°F is April 9, 16 days before the 32°F one. The freeze-free season lasts 205 days in a typical year, longer than at 92% of the 176 Pennsylvania stations; it reaches 225 days one year in ten and falls short of 182 one year in ten. On average 102 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 22, and return around October 20. Severe cold of 16°F or below comes in 99% of winters, usually between December 28 and February 23.

July is the warmest month at Harrisburg Cptl Cy Airport, PA, averaging 88°F by day and 67°F at night; January is the coldest at 40°F and 25°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 79% of years.

Warmth for growing adds up to 3,840 growing degree days a year (base 50°F), more than at 97% of the 176 Pennsylvania stations. 35% of them (1,351) have built up by the end of June, and July adds the most, 852. Precipitation totals 41.1 inches a year, most in July (4.3") and least in February (2.4"); May to September bring 47% of it.

The nearest other station, Harrisburg 1 NE, PA, 11 miles northeast of Grantham, has a last frost 6 days later (April 15), a first frost 9 days earlier (October 23), a season 16 days shorter.

The first measurable snow (0.1 inch or more) in Grantham 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, 11.1 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 23 days after the last snow.

ZIP 17027 is 9 miles from Harrisburg Cptl Cy Airport, PA, which stands at 340 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 17055 (Mechanicsburg). The 2023 USDA Plant Hardiness Zone Map lists ZIP 17027 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.