Pool season · Maryland
Frederick Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
This is the one-page view of Frederick'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.
Each dot on the bar is one week of Frederick'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 7–April 28), solid teal is swim season, and hollow amber is the closing window ending October 18. The black marker is today — its position against the colors is the entire executive summary.
The Frederick pool calendar
Opening — target April 14
Open by April 14 — a two-week head start on the April 28 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 18
The window opens October 8 once water leaves the algae zone; the model deadline is October 18, a week ahead of the November 6 freeze normal.
Estimated water temperature by month
This is Frederick'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° | 36° | 42° | 52° | 62° | 71° | 77° | 78° | 74° | 64° | 52° | 43° |
Warmest water typically August–August (peaking near 78°F); heaters and covers shift any month up.
Email me when Frederick hits the closing window
Data: NOAA 1991–2020 climate normals via Frederick Police Brks (1.8 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.