Frost Dates for 59421 — Cascade, Montana

Half of springs at Cascade 5 S, MT see their last 32°F night by May 21; only one in ten is past it by May 5, and one in ten still has one after June 6. Planting tender crops after May 27 leaves a 30% risk of a frost on them, after June 1 20%, and after June 6 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 40% of the 68 Montana stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 19 in half of years, as early as September 2 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 22, 15 days before the 32°F one. The freeze-free season lasts 120 days in a typical year, shorter than at 62% of the 68 Montana stations; it reaches 142 days one year in ten and falls short of 96 one year in ten. On average 146 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 June 8, and return around September 3. Severe cold of 16°F or below comes every winter, usually between October 29 and April 2.

July is the warmest month at Cascade 5 S, MT, averaging 86°F by day and 52°F at night; January is the coldest at 39°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 20% of years.

Warmth for growing adds up to 2,088 growing degree days a year (base 50°F), more than at 68% of the 68 Montana stations. 27% of them (564) have built up by the end of June, and July adds the most, 580. Precipitation totals 16.9 inches a year, most in May (3.0") and least in January (0.5"); May to September bring 59% of it.

The nearest other station, Great Falls International Airport, MT, 23 miles northeast of Cascade and 304 feet higher, has a last frost 2 days earlier (May 19), a first frost 5 days later (September 24), a season 6 days longer.

The first measurable snow (0.1 inch or more) in Cascade usually arrives around October 20, and the last of the season around April 21. Those are the middle dates across the winters of 1991–2020 at Cascade 5 S, MT, 0.3 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 30 days after the last snow.

ZIP 59421 is under a mile from Cascade 5 S, MT, which stands at 3,360 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59421 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.