Frost Dates for 17517 — Denver, Pennsylvania

Half of springs at Blue Marsh Lake, PA see their last 32°F night by April 26; only one in ten is past it by April 11, and one in ten still has one after May 12. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 7 20%, and after May 12 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 October 19 in half of years, as early as October 5 one year in ten, and holds off past November 3 one year in ten. A hard freeze of 28°F follows 13 days later, around November 1; in spring the one-in-ten date for 28°F is May 1, 11 days before the 32°F one. The freeze-free season lasts 176 days in a typical year, longer than at 52% of the 176 Pennsylvania stations; it reaches 198 days one year in ten and falls short of 152 one year in ten. On average 125 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 May 8, and return around October 8. Severe cold of 16°F or below comes every winter, usually between December 9 and March 8.

July is the warmest month at Blue Marsh Lake, PA, averaging 85°F by day and 63°F at night; January is the coldest at 37°F and 20°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 39% of years.

Warmth for growing adds up to 3,139 growing degree days a year (base 50°F), more than at 63% of the 176 Pennsylvania stations. 33% of them (1,036) have built up by the end of June, and July adds the most, 753. Precipitation totals 48.3 inches a year, most in July (5.2") and least in February (2.6"); May to September bring 48% of it.

The nearest other station, New Holland 2 SE, PA, 11 miles south of Denver and 255 feet higher, has a last frost 12 days earlier (April 14), a first frost 13 days later (November 1), a season 22 days longer.

The first measurable snow (0.1 inch or more) in Denver usually arrives around December 24, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Blue Marsh Lake, PA, 11.4 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 48 days after the last snow.

ZIP 17517 is 11 miles from Blue Marsh Lake, PA, which stands at 350 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 19608 (Sinking Spring). The 2023 USDA Plant Hardiness Zone Map lists ZIP 17517 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.