Frost dates for Great Falls Intl Airport, MT
At Great Falls Intl Airport, the median last spring frost (32°F) is May 19 and the median first fall frost is Sep 24, for a typical growing season of 126 days. For a 90% chance that the last frost has passed, wait until Jun 2. Nearby ZIP codes are in USDA hardiness zones 4a to 4b.
- May 19Last spring frost (median)50% chance of 32°F after this date
- Jun 2Safer planting date10% chance of 32°F after this date
- Sep 24First fall frost (median)50% chance of 32°F by this date
- 126 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 5 | Jun 25 |
| 32°F | May 7 | May 19 | Jun 2 |
| 28°F | Apr 23 | May 5 | May 18 |
| 24°F | Apr 6 | Apr 24 | May 8 |
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 27 | Sep 12 | Sep 26 |
| 32°F | Sep 9 | Sep 24 | Oct 5 |
| 28°F | Sep 20 | Oct 3 | Oct 18 |
| 24°F | Sep 30 | Oct 13 | Oct 29 |
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 | 69 days | 96 days | 117 days |
| 32°F | 107 days | 126 days | 143 days |
| 28°F | 132 days | 149 days | 168 days |
| 24°F | 150 days | 172 days | 195 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 |
|---|---|---|---|
| 59401 | 4b | -25 to -20°F | 9 km |
| 59414 | 4b | -25 to -20°F | 11 km |
| 59485 | 4a | -30 to -25°F | 15 km |
| 59404 | 4b | -25 to -20°F | 18 km |
| 59472 | 4b | -25 to -20°F | 20 km |
| 59405 | 4b | -25 to -20°F | 21 km |
| 59487 | 4a | -30 to -25°F | 23 km |
| 59483 | 4a | -30 to -25°F | 26 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 USW00024143, at 47.4733, -111.3822, elevation 1117 m (3,664 ft).
- Data quality: Standard (24+ years of data), 28 years of freeze data.
- Average days per year at or below 32°F: 168.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Great Falls WFO (1 km)
- Great Falls 16st (8 km)
- Sun River 4 S (27 km)
- Carter 14 W (37 km)
- Cascade 5 S (38 km)
- Fairfield (48 km)
- Raynesford 2 NNW (52 km)
- Cascade 20 SSE (55 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.