Pool season · Colorado
Westminster Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Westminster's whole pool calendar, condensed: when the water warms, when it cools, and where today falls between those edges. Use the opening guide and closing guide for the step-by-step work; keep this page for the dates.
Westminster, CO — 109 swim days a yearReading it takes ten seconds: 52 dots, one per week. Solid teal is Westminster's swim season; the hollow teal run before it (May 2 to May 23) is when to open; the hollow amber run after is when to close, with October 4 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The Westminster pool calendar
Opening — target May 9
Open by May 9 — a two-week head start on the May 23 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 4
The window opens September 25 once water leaves the algae zone; the model deadline is October 4, a week ahead of the October 11 freeze normal.
Estimated water temperature by month
This is Westminster'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 33° | 34° | 39° | 47° | 54° | 65° | 73° | 75° | 70° | 58° | 46° | 36° |
The curve peaks near 75°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Thornton's pool season and Arvada's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Colorado season index.
Westminster pool season FAQ
When should I open my pool in Westminster, CO?
Target May 9. That date backs off two weeks from the day Westminster's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Westminster opening guide.
When should I close my pool in Westminster?
The closing deadline is October 4 — late enough that the water has cooled out of the algae zone, early enough to beat Westminster's first-freeze normal by about a week. See the Westminster closing guide for the winterizing steps.
How long is the swim season in Westminster?
Westminster averages 109 days a year with normal highs of 80°F or better — about 4 days earlier than the Colorado median. The Colorado season index ranks all 19 covered cities by the same metric.
How warm does pool water get in Westminster?
An unheated pool near Westminster typically peaks around 75°F in high summer and bottoms out near 33°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 Westminster hits the closing window
Data: NOAA 1991–2020 climate normals via Northglenn (2.8 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.