Pool season · Maryland
Columbia Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
One bar, one year, one Columbia 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 Columbia's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (April 10–May 1), solid teal is swim season, and hollow amber is the closing window ending October 21. The black marker is today — its position against the colors is the entire executive summary.
The Columbia pool calendar
Opening — target April 17
Open by April 17 — a two-week head start on the May 1 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 21
Hold the cover until October 11, then winterize by October 21, a week ahead of the November 9 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is Columbia'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 36° | 35° | 41° | 51° | 61° | 70° | 78° | 79° | 75° | 65° | 53° | 43° |
Warmest water typically July–August (peaking near 79°F); heaters and covers shift any month up.
Email me when Columbia hits the closing window
Data: NOAA 1991–2020 climate normals via Laurel 3 W (8.3 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.