Frost Dates for 19809 — Wilmington, Delaware

Half of springs at Wilmington Porter Rsch, DE see their last 32°F night by April 7; only one in ten is past it by March 26, and one in ten still has one after April 24. Planting tender crops after April 13 leaves a 30% risk of a frost on them, after April 18 20%, and after April 24 10%. The 17 days between the even-odds date and the one-in-ten date is the widest of the 10 Delaware stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 4 in half of years, as early as October 21 one year in ten, and holds off past November 19 one year in ten. A hard freeze of 28°F follows 11 days later, around November 15; in spring the one-in-ten date for 28°F is April 10, 14 days before the 32°F one. The freeze-free season lasts 209 days in a typical year, shorter than at 50% of the 10 Delaware stations; it reaches 229 days one year in ten and falls short of 189 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 13 days longer, to about April 20, and return around October 24. Severe cold of 16°F or below comes every winter, usually between December 26 and February 26.

July is the warmest month at Wilmington Porter Rsch, DE, averaging 84°F by day and 67°F at night; January is the coldest at 38°F and 24°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 76% of years.

Warmth for growing adds up to 3,419 growing degree days a year (base 50°F), fewer than at 90% of the 10 Delaware stations. 33% of them (1,138) have built up by the end of June, and July adds the most, 794. Precipitation totals 50.5 inches a year, most in July (5.2") and least in February (3.0"); May to September bring 46% of it.

The nearest other station, Marcus Hook, PA, 5 miles northeast of Wilmington and 260 feet lower, has a last frost 8 days earlier (March 30), a first frost 12 days later (November 16), a season 21 days longer.

The first measurable snow (0.1 inch or more) in Wilmington usually arrives around January 8, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Wilmington Porter Rsch, DE, 2.4 miles away: half of years saw snow earlier, half later. Snow fell in 92% of those winters. The last 32°F night of spring typically comes 29 days after the last snow.

ZIP 19809 is 2 miles from Wilmington Porter Rsch, DE, which stands at 270 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 19805 (Wilmington). The 2023 USDA Plant Hardiness Zone Map lists ZIP 19809 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.