Pool season · Michigan
Ann Arbor Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
One bar, one year, one Ann Arbor 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.
Ann Arbor, MI — 74 swim days a yearThe bar compresses Ann Arbor's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 4–May 25 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 Ann Arbor pool calendar
Opening — target May 11
Open by May 11 — a two-week head start on the May 25 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 10 freeze normal.
Estimated water temperature by month
This is Ann Arbor'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 26° | 24° | 30° | 41° | 53° | 64° | 70° | 71° | 67° | 56° | 44° | 33° |
The curve peaks near 71°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Wyoming's pool season and Battle Creek's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Michigan season index.
Ann Arbor pool season FAQ
When should I open my pool in Ann Arbor, MI?
Open by May 11 — the model places Ann Arbor's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The Ann Arbor opening guide has the 12-step sequence.
When should I close my pool in Ann Arbor?
Close by September 29: cool water keeps its winter chemistry, but freeze damage is the hard stop. The Ann Arbor closing guide sequences the work backward from that date.
How long is the swim season in Ann Arbor?
Ann Arbor averages 74 days a year with normal highs of 80°F or better — right on the statewide median. The Michigan season index ranks all 23 covered cities by the same metric.
How warm does pool water get in Ann Arbor?
An unheated pool near Ann Arbor typically peaks around 71°F in high summer and bottoms out near 23°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 Ann Arbor hits the closing window
Data: NOAA 1991–2020 climate normals via Ann Arbor SE (3.0 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.