Pool season · California
San Mateo Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
This is the one-page view of San Mateo'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 San Mateo's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (May 7–May 28), solid teal is swim season, and hollow amber is the closing window ending November 6. The black marker is today — its position against the colors is the entire executive summary.
The San Mateo pool calendar
Opening — target May 14
Open by May 14 — a two-week head start on the May 28 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline November 6
The window opens October 27 once water leaves the algae zone; the model deadline is November 6, a week ahead of the December 26 freeze normal.
Estimated water temperature by month
This is San Mateo'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 51° | 52° | 55° | 56° | 59° | 61° | 63° | 64° | 65° | 64° | 60° | 53° |
The curve peaks near 65°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when San Mateo hits the closing window
Data: NOAA 1991–2020 climate normals via San Francisco International Airport (5.5 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.