Pool season · Colorado
Thornton Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
One bar, one year, one Thornton pool. The season bar below draws everything the model knows — opening window, prime season, closing window — against today's date, with the working details one click away on the opening and closing pages.
Each dot on the bar is one week of Thornton's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (May 2–May 23), solid teal is swim season, and hollow amber is the closing window ending October 4. The black marker is today — its position against the colors is the entire executive summary.
The Thornton pool calendar
Opening — target May 9
Target May 9; the practical window runs May 2–May 23, and the 7-day mean crosses the 61°F threshold around May 23. Cold-water starts are the cheap ones.
Closing — deadline October 4
Hold the cover until September 25, then winterize by October 4, a week ahead of the October 11 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on Thornton'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 33° | 34° | 39° | 47° | 54° | 65° | 73° | 75° | 70° | 58° | 46° | 36° |
The curve peaks near 75°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Thornton hits the closing window
Data: NOAA 1991–2020 climate normals via Northglenn (4.0 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.