Pool season · State index
Montana Pool Season 2026: Opening & Closing Dates by City
Last updated: July 25, 2026 · 2 cities covered
Both halves of the pool year for all 2 covered Montana cities. The median calendar runs May 29 to September 22. Every row links to a one-page season overview with the live water-temperature model; the opening and closing hubs carry the full checklists.
Montana: a short-season pool state| City | Open by | Close by | 80°F+ days |
|---|---|---|---|
| Billings | May 20 | Sep 27 | 72 |
| Missoula | Jun 7 | Sep 18 | 57 |
What the columns mean
"Open by" is the recommended spring date — two weeks before the city's 7-day mean temperature crosses 61°F, the model's proxy for water approaching the 65°F algae-growth zone. "Close by" is the fall deadline — ten days after the water leaves that zone, capped a week ahead of the local 50% first-freeze date. "80°F+ days" counts days whose normal high reaches 80°F: the length of the true warm-swim season, and the fairest single number for comparing Montana cities against each other.
Every figure comes from each city's own NOAA 1991–2020 normals station (named in its guide's footer), so neighboring cities can legitimately differ by a few days. The season overview linked from each row adds the live water-temperature model and the full-year season bar; the state hubs above carry the step-by-step checklists.
Swim-season length across Montana
The fairest way to compare Montana cities is the number of days with 80°F+ normal highs — the practical warm-swim season. Every bar links to that city's one-page season overview with the live water model.
Montana pool climate at a glance
Big Sky winters are long and springs fickle, so Montana pools squeeze into a brief July and August core, with mountain towns cooler than the eastern plains. In model terms that makes Montana a short-season state. The spread shows up clearly on the local pages: compare Billings's pool season with Missoula's and the difference is measured in weeks, not days. Neighbors in the index run on their own normals too — see Missouri and Nebraska for the adjacent calendars.
Montana pool season FAQ
When do pools open in Montana?
Model openings in Montana run from May 20 in Billings to June 7 in Missoula, with the statewide median on June 7. Each date is two weeks before that city's 7-day mean temperature crosses 61°F — early enough to start up in algae-cold water.
When should you close a pool in Montana?
The median Montana closing deadline is September 27, and every city's own deadline is capped a week ahead of its NOAA 50% first-freeze date. Closing late and cold beats closing early and warm — cool water holds its winter chemistry far better.
Which Montana city has the longest swim season?
Billings leads with 72 days of 80°F+ highs per year, while Missoula brings up the rear at 57 days. The chart above ranks every covered city by the same metric.