Frost Dates for 21755 — Jefferson, Maryland

Half of springs at Frederick Police Brks, MD see their last 32°F night by April 2; only one in ten is past it by March 17, and one in ten still has one after April 15. Planting tender crops after April 7 leaves a 30% risk of a frost on them, after April 11 20%, and after April 15 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 80% of the 50 Maryland stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 6 in half of years, as early as October 23 one year in ten, and holds off past November 24 one year in ten. A hard freeze of 28°F follows 15 days later, around November 21; in spring the one-in-ten date for 28°F is April 4, 11 days before the 32°F one. The freeze-free season lasts 218 days in a typical year, longer than at 72% of the 50 Maryland stations; it reaches 239 days one year in ten and falls short of 196 one year in ten. On average 84 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 15, and return around October 24. Severe cold of 16°F or below comes in 94% of winters, usually between January 4 and February 10.

July is the warmest month at Frederick Police Brks, MD, averaging 89°F by day and 68°F at night; January is the coldest at 43°F and 27°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 55% of years.

Warmth for growing adds up to 4,174 growing degree days a year (base 50°F), more than at 68% of the 50 Maryland stations. 37% of them (1,529) have built up by the end of June, and July adds the most, 883. Precipitation totals 43.8 inches a year, most in September (5.8") and least in January (2.6"); May to September bring 48% of it.

The nearest other station, Sharpsburg 5 S, MD, 9 miles west of Jefferson, has a last frost 24 days later (April 26), a first frost 19 days earlier (October 18), a season 43 days shorter.

The first measurable snow (0.1 inch or more) in Jefferson usually arrives around December 13, and the last of the season around March 7. Those are the middle dates across the winters of 1991–2020 at Sharpsburg 5 S, MD, 8.9 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 26 days after the last snow.

ZIP 21755 is 7 miles from Frederick Police Brks, MD, which stands at 380 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 21702 (Frederick). The 2023 USDA Plant Hardiness Zone Map lists ZIP 21755 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.