Pool season · Wisconsin
Madison Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
This is the one-page view of Madison'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.
Madison, WI — 63 swim days a yearThe bar compresses Madison's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 3–May 24 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends September 29. Wherever the today marker sits, the nearest color change is your next appointment.
The Madison pool calendar
Opening — target May 10
Open by May 10 — a two-week head start on the May 24 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline September 29
The window opens September 19 once water leaves the algae zone; the model deadline is September 29, a week ahead of the October 9 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Madison'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 22° | 20° | 29° | 41° | 53° | 64° | 71° | 71° | 67° | 56° | 44° | 31° |
The curve peaks near 72°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with La Crosse's pool season and Milwaukee's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Wisconsin season index.
Madison pool season FAQ
When should I open my pool in Madison, WI?
The site model recommends opening by May 10 — about two weeks before Madison'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 Madison opening guide.
When should I close my pool in Madison?
Winterize by September 29. The model holds the deadline a week ahead of Madison's NOAA 50% first-freeze date, so the plumbing is protected before the first hard night. The full sequence is in the Madison closing guide.
How long is the swim season in Madison?
Madison averages 63 days a year with normal highs of 80°F or better — right on the statewide median. The Wisconsin season index ranks all 11 covered cities by the same metric.
How warm does pool water get in Madison?
An unheated pool near Madison typically peaks around 72°F in high summer and bottoms out near 19°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 Madison hits the closing window
Data: NOAA 1991–2020 climate normals via Uw Arboretum - Madison (3.4 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.