Pool season · Washington
Seattle Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Seattle'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.
Seattle, WA — 0 swim days a yearThe bar compresses Seattle's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 24–June 14 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends October 1. Wherever the today marker sits, the nearest color change is your next appointment.
The Seattle pool calendar
Opening — target May 31
Open by May 31 — a two-week head start on the June 14 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline October 1
The window opens September 21 once water leaves the algae zone; the model deadline is October 1, a week ahead of the November 23 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Seattle's own normals — the shape of a typical year, not a forecast. The widget above shows where the current year actually sits.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 42° | 43° | 45° | 49° | 54° | 60° | 64° | 68° | 65° | 58° | 50° | 44° |
The curve peaks near 68°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Renton's pool season and Spokane's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Washington season index.
Seattle pool season FAQ
When should I open my pool in Seattle, WA?
The site model recommends opening by May 31 — about two weeks before Seattle's 7-day mean temperature crosses 61°F, while the water is still too cold for algae. The step-by-step sequence is in the Seattle opening guide.
When should I close my pool in Seattle?
Winterize by October 1. The model holds the deadline a week ahead of Seattle's NOAA 50% first-freeze date, so the plumbing is protected before the first hard night. The full sequence is in the Seattle closing guide.
How long is the swim season in Seattle?
Seattle averages 0 days a year with normal highs of 80°F or better — about 7 days later than the Washington median. The Washington season index ranks all 21 covered cities by the same metric.
How warm does pool water get in Seattle?
An unheated pool near Seattle typically peaks around 68°F in high summer and bottoms out near 41°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 Seattle hits the closing window
Data: NOAA 1991–2020 climate normals via Seattle Sand Pt WSFO (5.6 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.