Frost Dates for 59301 — Miles City, Montana

Half of springs at Miles City F Wiley Field, MT see their last 32°F night by May 8; only one in ten is past it by April 26, and one in ten still has one after May 21. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 17 20%, and after May 21 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 74% of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 30 in half of years, as early as September 17 one year in ten, and holds off past October 14 one year in ten. A hard freeze of 28°F follows 8 days later, around October 8; in spring the one-in-ten date for 28°F is May 12, 9 days before the 32°F one. The freeze-free season lasts 144 days in a typical year, longer than at 87% of the 68 Montana stations; it reaches 162 days one year in ten and falls short of 126 one year in ten. On average 166 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 10 days longer, to about May 18, and return around September 23. Severe cold of 16°F or below comes every winter, usually between November 6 and March 28.

July is the warmest month at Miles City F Wiley Field, MT, averaging 89°F by day and 60°F at night; January is the coldest at 30°F and 9°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 79% of years.

Warmth for growing adds up to 2,630 growing degree days a year (base 50°F), more than at 99% of the 68 Montana stations. 28% of them (747) have built up by the end of June, and July adds the most, 748. Precipitation totals 12.9 inches a year, most in May (2.7") and least in December (0.2"); May to September bring 67% of it.

The first measurable snow (0.1 inch or more) in Miles City usually arrives around October 31, and the last of the season around April 12. Those are the middle dates across the winters of 1991–2020 at Mizpah 4 NNW, MT, 25.1 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 59301 is 7 miles from Miles City F Wiley Field, MT, which stands at 2,624 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59301 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.