Frost Dates for 01821 — Billerica, Massachusetts

Half of springs at Bedford, MA see their last 32°F night by April 27; only one in ten is past it by April 13, and one in ten still has one after May 11. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 5 20%, and after May 11 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 51% of the 71 Massachusetts stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 13 in half of years, as early as October 1 one year in ten, and holds off past October 29 one year in ten. A hard freeze of 28°F follows 14 days later, around October 27; in spring the one-in-ten date for 28°F is April 26, 15 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, shorter than at 46% of the 71 Massachusetts stations; it reaches 189 days one year in ten and falls short of 150 one year in ten. On average 140 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 12 days longer, to about May 9, and return around October 3. Severe cold of 16°F or below comes every winter, usually between December 2 and March 13.

July is the warmest month at Bedford, MA, averaging 84°F by day and 61°F at night; January is the coldest at 36°F and 18°F. A freezing night is all but certain in every month from October 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 34% of years.

Warmth for growing adds up to 2,718 growing degree days a year (base 50°F), more than at 58% of the 71 Massachusetts stations. 31% of them (832) have built up by the end of June, and July adds the most, 700. Precipitation totals 49.0 inches a year, most in October (4.9") and least in February (3.4"); May to September bring 39% of it.

The nearest other station, Bedford Hanscom Field, MA, 6 miles south of Billerica, has a last frost 1 day later (April 28), a first frost 3 days earlier (October 10), a season 4 days shorter.

The first measurable snow (0.1 inch or more) in Billerica usually arrives around November 23, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Bedford, MA, 4.8 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 01821 is 5 miles from Bedford, MA, which stands at 160 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 01821 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.