Pool season · Arizona
Flagstaff Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Flagstaff's whole pool calendar, condensed: when the water warms, when it cools, and where today falls between those edges. Use the opening guide and closing guide for the step-by-step work; keep this page for the dates.
Flagstaff, AZ — 52 swim days a yearThe bar compresses Flagstaff's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 26–June 16 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends September 17. Wherever the today marker sits, the nearest color change is your next appointment.
The Flagstaff pool calendar
Opening — target June 2
Target June 2; the practical window runs May 26–June 16, and the 7-day mean crosses the 61°F threshold around June 16. Cold-water starts are the cheap ones.
Closing — deadline September 17
The window opens September 7 once water leaves the algae zone; the model deadline is September 17, a week ahead of the September 28 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Flagstaff's own normals — the shape of a typical year, not a forecast. The widget above shows where the current year actually sits.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 30° | 31° | 35° | 41° | 48° | 57° | 65° | 66° | 62° | 53° | 42° | 33° |
The curve peaks near 67°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Chandler's pool season and Gilbert's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Arizona season index.
Flagstaff pool season FAQ
When should I open my pool in Flagstaff, AZ?
The site model recommends opening by June 2 — about two weeks before Flagstaff's 7-day mean temperature crosses 61°F, while the water is still too cold for algae. The step-by-step sequence is in the Flagstaff opening guide.
When should I close my pool in Flagstaff?
Winterize by September 17. The model holds the deadline a week ahead of Flagstaff's NOAA 50% first-freeze date, so the plumbing is protected before the first hard night. The full sequence is in the Flagstaff closing guide.
How long is the swim season in Flagstaff?
Flagstaff averages 52 days a year with normal highs of 80°F or better — about 97 days later than the Arizona median. The Arizona season index ranks all 20 covered cities by the same metric.
How warm does pool water get in Flagstaff?
An unheated pool near Flagstaff typically peaks around 67°F in high summer and bottoms out near 30°F in winter, never quite reaching the 78°F comfort line without a heater or solar cover. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when Flagstaff hits the closing window
Data: NOAA 1991–2020 climate normals via Flagstaff Pulliam Airport (4.0 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.