Frost Dates for 21561 — Swanton, Maryland

Half of springs at Savage Rvr Dam, MD see their last 32°F night by April 29; only one in ten is past it by April 11, and one in ten still has one after May 15. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 9 20%, and after May 15 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 50% of the 50 Maryland stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 20 in half of years, as early as October 4 one year in ten, and holds off past November 2 one year in ten. A hard freeze of 28°F follows 12 days later, around November 1; in spring the one-in-ten date for 28°F is May 1, 14 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, shorter than at 90% of the 50 Maryland stations; it reaches 196 days one year in ten and falls short of 151 one year in ten. On average 130 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 9 days longer, to about May 8, and return around October 6. Severe cold of 16°F or below comes every winter, usually between December 8 and March 8.

July is the warmest month at Savage Rvr Dam, MD, averaging 81°F by day and 60°F at night; January is the coldest at 36°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 42% of years.

Warmth for growing adds up to 2,642 growing degree days a year (base 50°F), fewer than at 94% of the 50 Maryland stations. 33% of them (881) have built up by the end of June, and July adds the most, 639. Precipitation totals 41.4 inches a year, most in May (4.6") and least in November (2.4"); May to September bring 50% of it.

The nearest other station, Sines Deep Creek, MD, 11 miles west of Swanton and 545 feet higher, has a last frost 10 days later (May 9), a first frost 9 days earlier (October 11), a season 19 days shorter.

The first measurable snow (0.1 inch or more) in Swanton usually arrives around December 14, and the last of the season around March 6. Those are the middle dates across the winters of 1991–2020 at Savage Rvr Dam, MD, 4.1 miles away: half of years saw snow earlier, half later. Snow fell in 86% of those winters. The last 32°F night of spring typically comes 54 days after the last snow.

ZIP 21561 is 4 miles from Savage Rvr Dam, MD, which stands at 1,495 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 21561 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.