Frost Dates for 18106 — Allentown, Pennsylvania

Half of springs at Rodale Rsch Ctr, PA see their last 32°F night by April 26; only one in ten is past it by April 10, and one in ten still has one after May 13. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 7 20%, and after May 13 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 14 in half of years, as early as October 1 one year in ten, and holds off past October 31 one year in ten. A hard freeze of 28°F follows 12 days later, around October 26; in spring the one-in-ten date for 28°F is April 29, 14 days before the 32°F one. The freeze-free season lasts 171 days in a typical year, shorter than at 57% of the 176 Pennsylvania stations; it reaches 194 days one year in ten and falls short of 150 one year in ten. On average 131 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 5. Severe cold of 16°F or below comes every winter, usually between December 6 and March 9.

July is the warmest month at Rodale Rsch Ctr, PA, averaging 85°F by day and 62°F at night; January is the coldest at 38°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 37% of years.

Warmth for growing adds up to 3,067 growing degree days a year (base 50°F), more than at 57% of the 176 Pennsylvania stations. 33% of them (1,020) have built up by the end of June, and July adds the most, 733. Precipitation totals 48.8 inches a year, most in July (5.4") and least in February (2.8"); May to September bring 47% of it.

The nearest other station, Allentown International Airport, PA, 9 miles northeast of Allentown and 160 feet lower, has a last frost 6 days earlier (April 20), a first frost 10 days later (October 24), a season 13 days longer.

The first measurable snow (0.1 inch or more) in Allentown usually arrives around December 6, and the last of the season around March 22. Those are the middle dates across the winters of 1991–2020 at Allentown International Airport, PA, 9.2 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 35 days after the last snow.

ZIP 18106 is 7 miles from Rodale Rsch Ctr, PA, which stands at 550 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 11 other ZIP codes share the station; its figures are presented in full for 18062 (Macungie). The 2023 USDA Plant Hardiness Zone Map lists ZIP 18106 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.