Pool season · Missouri
St. Louis Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
One bar, one year, one St. Louis 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.
St. Louis, MO — 118 swim days a yearReading it takes ten seconds: 52 dots, one per week. Solid teal is St. Louis's swim season; the hollow teal run before it (April 4 to April 25) is when to open; the hollow amber run after is when to close, with October 23 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The St. Louis pool calendar
Opening — target April 11
Target April 11; the practical window runs April 4–April 25, and the 7-day mean crosses the 61°F threshold around April 25. Cold-water starts are the cheap ones.
Closing — deadline October 23
Hold the cover until October 13, then winterize by October 23, a week ahead of the November 4 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is St. Louis's typical-year water curve: the same EWMA model as the live widget, run on the 1991–2020 normals instead of this week's weather.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 34° | 34° | 43° | 53° | 64° | 73° | 80° | 80° | 76° | 66° | 53° | 42° |
Warmest water typically July–August (peaking near 81°F); heaters and covers shift any month up.
Every station tells its own story: compare this curve with Springfield's pool season and Columbia's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Missouri season index.
St. Louis pool season FAQ
When should I open my pool in St. Louis, MO?
Open by April 11 — the model places St. Louis's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The St. Louis opening guide has the 12-step sequence.
When should I close my pool in St. Louis?
Close by October 23: cool water keeps its winter chemistry, but freeze damage is the hard stop. The St. Louis closing guide sequences the work backward from that date.
How long is the swim season in St. Louis?
St. Louis averages 118 days a year with normal highs of 80°F or better — about 7 days earlier than the Missouri median. The Missouri season index ranks all 8 covered cities by the same metric.
How warm does pool water get in St. Louis?
An unheated pool near St. Louis typically peaks around 81°F in high summer and bottoms out near 33°F in winter, spending roughly 2 months at or above the 78°F comfort line most swimmers prefer. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when St. Louis hits the closing window
Data: NOAA 1991–2020 climate normals via St Louis Sci Center (1.4 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.