Frost dates for Cascade 5 S, MT
At Cascade 5 S, the median last spring frost (32°F) is May 21 and the median first fall frost is Sep 19, for a typical growing season of 120 days. For a 90% chance that the last frost has passed, wait until Jun 6. Nearby ZIP codes are in USDA hardiness zones 4a to 4b.
- May 21Last spring frost (median)50% chance of 32°F after this date
- Jun 6Safer planting date10% chance of 32°F after this date
- Sep 19First fall frost (median)50% chance of 32°F by this date
- 120 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 22 | Jun 8 | Jun 27 |
| 32°F | May 5 | May 21 | Jun 6 |
| 28°F | Apr 22 | May 7 | May 22 |
| 24°F | Apr 6 | Apr 24 | May 10 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Aug 18 | Sep 3 | Sep 21 |
| 32°F | Sep 2 | Sep 19 | Oct 2 |
| 28°F | Sep 13 | Oct 1 | Oct 16 |
| 24°F | Sep 26 | Oct 12 | Oct 27 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 63 days | 88 days | 111 days |
| 32°F | 96 days | 120 days | 142 days |
| 28°F | 124 days | 145 days | 166 days |
| 24°F | 145 days | 168 days | 192 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
Closest ZIP codes (each is closer to another station)
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59421 | 4b | -25 to -20°F | 16 km |
| 59485 | 4a | -30 to -25°F | 26 km |
| 59483 | 4a | -30 to -25°F | 27 km |
| 59477 | 4b | -25 to -20°F | 32 km |
| 59405 | 4b | -25 to -20°F | 32 km |
| 59443 | 4b | -25 to -20°F | 39 km |
| 59648 | 4b | -25 to -20°F | 40 km |
| 59472 | 4b | -25 to -20°F | 40 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00241552, at 47.2192, -111.7106, elevation 1024 m (3,360 ft).
- Data quality: Standard (24+ years of data), 27 years of freeze data.
- Average days per year at or below 32°F: 146.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Adel (24 km)
- Cascade 20 SSE (27 km)
- Sun River 4 S (29 km)
- Holter Dam (34 km)
- Great Falls WFO (36 km)
- Great Falls Intl Airport (38 km)
- Rogers Pass 9 NNE (44 km)
- Great Falls 16st (44 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.