Pool season · Massachusetts
Somerville Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Somerville'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.
Somerville, MA — 54 swim days a yearThe bar compresses Somerville's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 5–May 26 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends October 8. Wherever the today marker sits, the nearest color change is your next appointment.
The Somerville pool calendar
Opening — target May 12
Target May 12; the practical window runs May 5–May 26, and the 7-day mean crosses the 61°F threshold around May 26. Cold-water starts are the cheap ones.
Closing — deadline October 8
Hold the cover until September 28, then winterize by October 8, a week ahead of the November 9 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on Somerville'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 32° | 30° | 35° | 44° | 54° | 64° | 72° | 74° | 70° | 60° | 49° | 40° |
The curve peaks near 74°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Quincy's pool season and Springfield's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Massachusetts season index.
Somerville pool season FAQ
When should I open my pool in Somerville, MA?
Target May 12. That date backs off two weeks from the day Somerville's 7-day mean temperature reaches 61°F, so you start up in cold, algae-resistant water. Work the full checklist in the Somerville opening guide.
When should I close my pool in Somerville?
The closing deadline is October 8 — late enough that the water has cooled out of the algae zone, early enough to beat Somerville's first-freeze normal by about a week. See the Somerville closing guide for the winterizing steps.
How long is the swim season in Somerville?
Somerville averages 54 days a year with normal highs of 80°F or better — right on the statewide median. The Massachusetts season index ranks all 14 covered cities by the same metric.
How warm does pool water get in Somerville?
An unheated pool near Somerville typically peaks around 74°F in high summer and bottoms out near 30°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 Somerville hits the closing window
Data: NOAA 1991–2020 climate normals via Boston Logan International Airport (5.1 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.