Frost dates · Montana
When is the first frost in Helena?
In a typical year, Helena’s first frost comes around September 30 and its last around May 9.
One year in ten the first frost comes as early as September 17, and nine years in ten it has arrived by October 11. One year in ten the last frost is over as early as April 29, and nine years in ten it is over by May 25. Helena averages about 170 nights a year at 32°F or colder, with about 142 frost-free days in between in a typical year. It’s frost season here, and the last frost usually comes around May 9. That makes it the 8th earliest first frost of the 117 cities we track where it freezes most years.
Last updated
A freeze is in the forecast for the next 48 hours.
Helena’s first frost turns up by the end of September, just as summer was getting comfortable.
Live 48-hour check from OpenWeatherMap, refreshed about every half hour. Alerts from the National Weather Service.
Frost dates, early, typical and late years
| Early year (1 in 10) | Typical | Late year (1 in 10) | |
|---|---|---|---|
| First frost | September 17 | September 30 | October 11 |
| Last frost | April 29 | May 9 | May 25 |
A frost date here is a night when the official thermometer reads 32°F or colder. Frost on the ground can show up on clear, calm nights a few degrees milder.
Cities with about the same first frost
- Fargo, North Dakota: first frost around September 30
- Anchorage, Alaska: first frost around October 1
- Cheyenne, Wyoming: first frost around October 1
Source: NOAA U.S. Climate Normals, 1991 to 2020, station USW00024144.