Frost Dates for 59701 — Butte, Montana

Half of springs at Butte Bert Mooney Airport, MT see their last 32°F night by June 13; only one in ten is past it by May 27, and one in ten still has one after July 1. Planting tender crops after June 21 leaves a 30% risk of a frost on them, after June 25 20%, and after July 1 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 68% of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 5 in half of years, as early as August 24 one year in ten, and holds off past September 19 one year in ten. A hard freeze of 28°F follows 12 days later, around September 17; in spring the one-in-ten date for 28°F is June 10, 21 days before the 32°F one. The freeze-free season lasts 83 days in a typical year, shorter than at 97% of the 68 Montana stations; it reaches 105 days one year in ten and falls short of 60 one year in ten. On average 220 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 23 and April 12.

July is the warmest month at Butte Bert Mooney Airport, MT, averaging 81°F by day and 46°F at night; December is the coldest at 31°F and 7°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). No month is safe from a 32°F night: even the warmest has at least a 10% chance. In spring, June still brings one in 80% of years and July still brings one in 10% of years.

Warmth for growing adds up to 1,210 growing degree days a year (base 50°F), fewer than at 96% of the 68 Montana stations. 21% of them (260) have built up by the end of June, and July adds the most, 422. Precipitation totals 12.7 inches a year, most in June (2.5") and least in January (0.4"); May to September bring 64% of it.

The nearest other station, Anaconda, MT, 22 miles northwest of Butte and 276 feet lower, has a last frost 12 days earlier (June 1), a first frost 9 days later (September 14), a season 22 days longer.

The first measurable snow (0.1 inch or more) in Butte usually arrives around October 6, and the last of the season around May 21. Those are the middle dates across the winters of 1991–2020 at Anaconda, MT, 22.2 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 23 days after the last snow.

ZIP 59701 is 2 miles from Butte Bert Mooney Airport, MT, which stands at 5,506 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59701 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.