Frost Dates for 20191 — Reston, Virginia

Half of springs at Vienna, VA see their last 32°F night by April 14; only one in ten is past it by March 30, and one in ten still has one after April 28. Planting tender crops after April 20 leaves a 30% risk of a frost on them, after April 23 20%, and after April 28 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 80% of the 128 Virginia stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 29 in half of years, as early as October 17 one year in ten, and holds off past November 11 one year in ten. A hard freeze of 28°F follows 10 days later, around November 8; in spring the one-in-ten date for 28°F is April 16, 12 days before the 32°F one. The freeze-free season lasts 198 days in a typical year, longer than at 51% of the 128 Virginia stations; it reaches 218 days one year in ten and falls short of 180 one year in ten. On average 99 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 11 days longer, to about April 25, and return around October 19. Severe cold of 16°F or below comes every winter, usually between December 25 and February 27.

July is the warmest month at Vienna, VA, averaging 84°F by day and 67°F at night; January is the coldest at 42°F and 23°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 85% of years.

Warmth for growing adds up to 3,472 growing degree days a year (base 50°F), fewer than at 69% of the 128 Virginia stations. 34% of them (1,197) have built up by the end of June, and July adds the most, 781. Precipitation totals 43.5 inches a year, most in May (4.3") and least in February (2.6"); May to September bring 47% of it.

The nearest other station, Washington Dc Dulles Airport, VA, 6 miles west of Reston, has a last frost 1 day later (April 15), a first frost 5 days earlier (October 24), a season 4 days shorter.

The first measurable snow (0.1 inch or more) in Reston usually arrives around December 10, and the last of the season around March 2. Those are the middle dates across the winters of 1991–2020 at Vienna, VA, 4.3 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 43 days after the last snow.

ZIP 20191 is 4 miles from Vienna, VA, which stands at 418 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 20 other ZIP codes share the station; its figures are presented in full for 22030 (Fairfax). The 2023 USDA Plant Hardiness Zone Map lists ZIP 20191 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.