Pool season · California
San Mateo Pool Season: the Year on One Bar
Last updated: July 25, 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.
San Mateo, CA — 0 swim days a yearEach 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.
Every station tells its own story: compare this curve with San Marcos's pool season and San Ramon's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the California season index.
San Mateo pool season FAQ
When should I open my pool in San Mateo, CA?
Open by May 14 — the model places San Mateo's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The San Mateo opening guide has the 12-step sequence.
When should I close my pool in San Mateo?
Close by November 6: cool water keeps its winter chemistry, but freeze damage is the hard stop. The San Mateo closing guide sequences the work backward from that date.
How long is the swim season in San Mateo?
San Mateo averages 0 days a year with normal highs of 80°F or better — about 43 days later than the California median. The California season index ranks all 147 covered cities by the same metric.
How warm does pool water get in San Mateo?
An unheated pool near San Mateo typically peaks around 65°F in high summer and bottoms out near 51°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 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.