Pool season · Missouri
O'Fallon Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
This is the one-page view of O'Fallon's pool year: both model windows, the estimated water-temperature curve, and today's live position on the season bar. The detailed checklists live on the opening and closing guides; this page is the calendar you check between them.
The bar compresses O'Fallon's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the April 11–May 2 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends October 14. Wherever the today marker sits, the nearest color change is your next appointment.
The O'Fallon pool calendar
Opening — target April 18
Target April 18; the practical window runs April 11–May 2, and the 7-day mean crosses the 61°F threshold around May 2. Cold-water starts are the cheap ones.
Closing — deadline October 14
Hold the cover until October 4, then winterize by October 14, a week ahead of the October 26 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on O'Fallon'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 32° | 32° | 40° | 50° | 61° | 70° | 76° | 77° | 73° | 62° | 51° | 39° |
The curve peaks near 77°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when O'Fallon hits the closing window
Data: NOAA 1991–2020 climate normals via Weldon Spring NWS (6.2 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.