Frost dates for Westby, MT
At this NOAA station the last spring frost (32°F) usually comes by May 18 and the first fall frost around September 21, giving a growing season of about 125 days.
May 18average last spring frost
September 21average first fall frost
JanAprJulOctDec
Frost odds
| 1 year in 10 the last spring frost is later than | May 30 |
| Half of years the last spring frost is later than | May 18 |
| 9 years in 10 the last spring frost is later than | May 6 |
| 1 year in 10 the first fall frost is earlier than | September 7 |
| Half of years the first fall frost is earlier than | September 21 |
| 9 years in 10 the first fall frost is earlier than | October 1 |
A hard freeze (28°F) usually ends by May 8 and returns around September 28.
A light frost (36°F, which can still nip tender plants) usually ends by May 27 and returns around September 12.
Station USC00248777, elevation 641 m. Based on 27 years of 1991 to 2020 records. A garden higher up, in a hollow or far from this station can freeze later in spring.
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Sources
- U.S. Annual/Seasonal Climate Normals, 1991 to 2020 (freeze probability dates by station), NOAA National Centers for Environmental Information, checked 1 November 2026
- Annual/Seasonal Normals 1991 to 2020 documentation, NOAA National Centers for Environmental Information, checked 1 November 2026
- 2024 Gazetteer Files, ZIP Code Tabulation Areas, US Census Bureau, checked 1 November 2026