Frost dates for Lewistown Muni Airport, MT
At Lewistown Muni Airport, the median last spring frost (32°F) is May 23 and the median first fall frost is Sep 21, for a typical growing season of 119 days. For a 90% chance that the last frost has passed, wait until Jun 8. Nearby ZIP codes are in USDA hardiness zone 4b.
- May 23Last spring frost (median)50% chance of 32°F after this date
- Jun 8Safer planting date10% chance of 32°F after this date
- Sep 21First fall frost (median)50% chance of 32°F by this date
- 119 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 26 | Jun 11 | Jul 3 |
| 32°F | May 11 | May 23 | Jun 8 |
| 28°F | Apr 27 | May 9 | May 24 |
| 24°F | Apr 11 | Apr 28 | May 11 |
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 24 | Sep 8 | Sep 21 |
| 32°F | Sep 8 | Sep 21 | Oct 3 |
| 28°F | Sep 18 | Oct 1 | Oct 15 |
| 24°F | Sep 26 | Oct 10 | Oct 25 |
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 | 60 days | 86 days | 108 days |
| 32°F | 98 days | 119 days | 138 days |
| 28°F | 125 days | 145 days | 162 days |
| 24°F | 146 days | 165 days | 187 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 |
|---|---|---|---|
| 59457 | 4b | -25 to -20°F | 15 km |
| 59464 | 4b | -25 to -20°F | 26 km |
| 59462 | 4b | -25 to -20°F | 34 km |
| 59451 | 4b | -25 to -20°F | 38 km |
| 59441 | 4b | -25 to -20°F | 38 km |
| 59418 | 4b | -25 to -20°F | 41 km |
| 59453 | 4b | -25 to -20°F | 48 km |
| 59430 | 4b | -25 to -20°F | 49 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 USW00024036, at 47.0492, -109.4578, elevation 1263 m (4,145 ft).
- Data quality: Standard (24+ years of data), 30 years of freeze data.
- Average days per year at or below 32°F: 184.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Lewistown (4 km)
- Lewistown 11 SSE (16 km)
- Lewistown 11ese (18 km)
- Moccasin Exp. Station (37 km)
- Judith Gap (47 km)
- Denton (47 km)
- Judith Gap 13 E (49 km)
- Grass Range (50 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.