Frost Dates for 17516 — Conestoga, Pennsylvania

Half of springs at Safe Harbor Dam, PA see their last 32°F night by April 1; only one in ten is past it by March 18, and one in ten still has one after April 13. Planting tender crops after April 6 leaves a 30% risk of a frost on them, after April 9 20%, and after April 13 10%. The 12 days between the even-odds date and the one-in-ten date is narrower than at 99% of the 176 Pennsylvania stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 10 in half of years, as early as October 28 one year in ten, and holds off past November 25 one year in ten. A hard freeze of 28°F follows 12 days later, around November 22; in spring the one-in-ten date for 28°F is April 1, 12 days before the 32°F one. The freeze-free season lasts 221 days in a typical year, longer than at 98% of the 176 Pennsylvania stations; it reaches 241 days one year in ten and falls short of 202 one year in ten. On average 87 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 12 days longer, to about April 13, and return around November 1. Severe cold of 16°F or below comes in 97% of winters, usually between January 4 and February 19.

July is the warmest month at Safe Harbor Dam, PA, averaging 87°F by day and 68°F at night; January is the coldest at 39°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 52% of years.

Warmth for growing adds up to 3,703 growing degree days a year (base 50°F), more than at 95% of the 176 Pennsylvania stations. 34% of them (1,258) have built up by the end of June, and July adds the most, 845. Precipitation totals 46.5 inches a year, most in September (4.9") and least in February (2.7"); May to September bring 46% of it.

The nearest other station, Lancaster 2NE Fltr Plt, PA, 9 miles northeast of Conestoga, has a last frost 18 days later (April 19), a first frost 17 days earlier (October 24), a season 35 days shorter.

The first measurable snow (0.1 inch or more) in Conestoga usually arrives around December 27, and the last of the season around March 7. Those are the middle dates across the winters of 1991–2020 at Safe Harbor Dam, PA, 1.8 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 25 days after the last snow.

ZIP 17516 is 2 miles from Safe Harbor Dam, PA, which stands at 195 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 9 other ZIP codes share the station; its figures are presented in full for 17551 (Millersville). The 2023 USDA Plant Hardiness Zone Map lists ZIP 17516 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.