Frost Dates for 59833 — Florence, Montana

Half of springs at Stevensville, MT see their last 32°F night by May 22; only one in ten is past it by May 7, and one in ten still has one after June 13. Planting tender crops after May 30 leaves a 30% risk of a frost on them, after June 4 20%, and after June 13 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 93% of the 68 Montana stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by September 19 in half of years, as early as September 3 one year in ten, and holds off past October 2 one year in ten. A hard freeze of 28°F follows 12 days later, around October 1; in spring the one-in-ten date for 28°F is May 19, 25 days before the 32°F one. The freeze-free season lasts 115 days in a typical year, shorter than at 71% of the 68 Montana stations; it reaches 139 days one year in ten and falls short of 87 one year in ten. On average 175 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between November 7 and March 13.

July is the warmest month at Stevensville, MT, averaging 85°F by day and 49°F at night; December is the coldest at 33°F and 19°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 24% of years.

Warmth for growing adds up to 1,760 growing degree days a year (base 50°F), fewer than at 63% of the 68 Montana stations. 27% of them (478) have built up by the end of June, and July adds the most, 532. Precipitation totals 12.4 inches a year, most in June (1.6") and least in March (0.8"); May to September bring 44% of it.

The nearest other station, Missoula 2 NE, MT, 18 miles north of Florence, has a last frost 12 days earlier (May 10), a first frost 12 days later (October 1), a season 28 days longer.

The first measurable snow (0.1 inch or more) in Florence usually arrives around November 1, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Missoula 2 NE, MT, 18.4 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 39 days after the last snow.

ZIP 59833 is 9 miles from Stevensville, MT, which stands at 3,375 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 59870 (Stevensville). The 2023 USDA Plant Hardiness Zone Map lists ZIP 59833 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.