Pool season · California
Union City Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
Union City'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.
Reading it takes ten seconds: 52 dots, one per week. Solid teal is Union City's swim season; the hollow teal run before it (April 21 to May 12) is when to open; the hollow amber run after is when to close, with November 2 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The Union City pool calendar
Opening — target April 28
Open by April 28 — a two-week head start on the May 12 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline November 2
The window opens October 23 once water leaves the algae zone; the model deadline is November 2, a week ahead of the December 22 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Union City'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 50° | 52° | 55° | 57° | 60° | 63° | 67° | 68° | 68° | 65° | 59° | 52° |
The curve peaks near 68°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Union City hits the closing window
Data: NOAA 1991–2020 climate normals via Fremont (4.2 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.