Frost Dates for 20837 — Poolesville, Maryland

Half of springs at WFO Sterling, VA see their last 32°F night by April 13; only one in ten is past it by March 29, and one in ten still has one after May 1. Planting tender crops after April 19 leaves a 30% risk of a frost on them, after April 24 20%, and after May 1 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 76% of the 50 Maryland stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 26 in half of years, as early as October 11 one year in ten, and holds off past November 7 one year in ten. A hard freeze of 28°F follows 9 days later, around November 4; in spring the one-in-ten date for 28°F is April 14, 17 days before the 32°F one. The freeze-free season lasts 195 days in a typical year, shorter than at 68% of the 50 Maryland stations; it reaches 215 days one year in ten and falls short of 173 one year in ten. On average 119 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 15 days longer, to about April 28, and return around October 16. Severe cold of 16°F or below comes every winter, usually between December 20 and February 25.

July is the warmest month at WFO Sterling, VA, averaging 87°F by day and 67°F at night; January is the coldest at 42°F and 25°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 83% of years and May still brings one in 12% of years.

Warmth for growing adds up to 3,865 growing degree days a year (base 50°F), fewer than at 56% of the 50 Maryland stations. 35% of them (1,364) have built up by the end of June, and July adds the most, 845. Precipitation totals 45.1 inches a year, most in May (4.9") and least in February (2.6"); May to September bring 47% of it.

The nearest other station, Damascus 3 SSW, MD, 13 miles northeast of Poolesville and 412 feet higher, has a last frost 1 day later (April 14), a first frost 3 days later (October 29), a season 1 day longer.

The first measurable snow (0.1 inch or more) in Poolesville usually arrives around December 14, and the last of the season around March 13. Those are the middle dates across the winters of 1991–2020 at WFO Sterling, VA, 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 31 days after the last snow.

ZIP 20837 is 11 miles from WFO Sterling, VA, which stands at 288 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 20147 (Ashburn). The 2023 USDA Plant Hardiness Zone Map lists ZIP 20837 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.