Pool season · Maryland
Frederick Pool Season: the Year on One Bar
Last updated: July 25, 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.
Frederick, MD — 112 swim days a yearEach 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.
Every station tells its own story: compare this curve with Ellicott City's pool season and Germantown's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Maryland season index.
Frederick pool season FAQ
When should I open my pool in Frederick, MD?
Target April 14. That date backs off two weeks from the day Frederick's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Frederick opening guide.
When should I close my pool in Frederick?
The closing deadline is October 18 — late enough that the water has cooled out of the algae zone, early enough to beat Frederick's first-freeze normal by about a week. See the Frederick closing guide for the winterizing steps.
How long is the swim season in Frederick?
Frederick averages 112 days a year with normal highs of 80°F or better — about 6 days earlier than the Maryland median. The Maryland season index ranks all 9 covered cities by the same metric.
How warm does pool water get in Frederick?
An unheated pool near Frederick typically peaks around 78°F in high summer and bottoms out near 35°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 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.