Frost Dates for 59436 — Fairfield, Montana

Half of springs at Fairfield, MT see their last 32°F night by May 13; only one in ten is past it by April 28, and one in ten still has one after June 1. Planting tender crops after May 20 leaves a 30% risk of a frost on them, after May 25 20%, and after June 1 10%. The 19 days between the even-odds date and the one-in-ten date is wider than at 78% of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 27 in half of years, as early as September 14 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 10 days later, around October 7; in spring the one-in-ten date for 28°F is May 14, 18 days before the 32°F one. The freeze-free season lasts 135 days in a typical year, longer than at 66% of the 68 Montana stations; it reaches 155 days one year in ten and falls short of 115 one year in ten. On average 160 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 18 days longer, to about May 31, and return around September 15. Severe cold of 16°F or below comes every winter, usually between November 2 and April 1.

July is the warmest month at Fairfield, MT, averaging 80°F by day and 53°F at night; January is the coldest at 36°F and 17°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 83% of years and June still brings one in 10% of years.

Warmth for growing adds up to 1,732 growing degree days a year (base 50°F), fewer than at 69% of the 68 Montana stations. 25% of them (436) have built up by the end of June, and July adds the most, 512. Precipitation totals 12.3 inches a year, most in June (2.6") and least in January (0.3"); May to September bring 66% of it.

The nearest other station, Bynum 4 SSE, MT, 24 miles northwest of Fairfield, has a last frost 3 days later (May 16), the same first-frost date, a season 2 days shorter.

The first measurable snow (0.1 inch or more) in Fairfield usually arrives around October 10, and the last of the season around May 12. Those are the middle dates across the winters of 1991–2020 at Simms 1 NE, MT, 10.4 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 1 day after the last snow.

ZIP 59436 is 2 miles from Fairfield, MT, which stands at 3,983 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59436 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.