Frost dates for Great Falls 16st, MT
At Great Falls 16st, the median last spring frost (32°F) is May 6 and the median first fall frost is Oct 1, for a typical growing season of 147 days. For a 90% chance that the last frost has passed, wait until May 19. Nearby ZIP codes are in USDA hardiness zone 4b.
- May 6Last spring frost (median)50% chance of 32°F after this date
- May 19Safer planting date10% chance of 32°F after this date
- Oct 1First fall frost (median)50% chance of 32°F by this date
- 147 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 6 | May 19 | Jun 1 |
| 32°F | Apr 23 | May 6 | May 19 |
| 28°F | Apr 7 | Apr 24 | May 8 |
| 24°F | Mar 28 | Apr 13 | Apr 30 |
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 | Sep 7 | Sep 21 | Oct 3 |
| 32°F | Sep 17 | Oct 1 | Oct 16 |
| 28°F | Sep 25 | Oct 11 | Oct 29 |
| 24°F | Oct 2 | Oct 24 | Nov 8 |
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 | 105 days | 124 days | 142 days |
| 32°F | 129 days | 147 days | 166 days |
| 28°F | 149 days | 171 days | 193 days |
| 24°F | 166 days | 191 days | 216 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 59401 | 4b | -25 to -20°F | 3 km |
| 59414 | 4b | -25 to -20°F | 5 km |
| 59404 | 4b | -25 to -20°F | 16 km |
| 59472 | 4b | -25 to -20°F | 17 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 USC00243749, at 47.4883, -111.2792, elevation 1068 m (3,505 ft).
- Data quality: Representative (10+ years), 14 years of freeze data.
- Average days per year at or below 32°F: 143.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Great Falls Intl Airport (8 km)
- Great Falls WFO (8 km)
- Carter 14 W (34 km)
- Sun River 4 S (34 km)
- Cascade 5 S (44 km)
- Raynesford 2 NNW (45 km)
- Highwood 7 NE (49 km)
- Shonkin 7 S (53 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.