Pool season · South Carolina
Sumter Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Sumter'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.
Sumter, SC — 142 swim days a yearEach dot on the bar is one week of Sumter's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (March 21–April 11), solid teal is swim season, and hollow amber is the closing window ending October 30. The black marker is today — its position against the colors is the entire executive summary.
The Sumter pool calendar
Opening — target March 28
Target March 28; the practical window runs March 21–April 11, and the 7-day mean crosses the 61°F threshold around April 11. Cold-water starts are the cheap ones.
Closing — deadline October 30
Hold the cover until October 20, then winterize by October 30, a week ahead of the November 7 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is Sumter'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 45° | 45° | 50° | 58° | 66° | 74° | 79° | 79° | 76° | 68° | 57° | 49° |
Warmest water typically July–August (peaking near 80°F); heaters and covers shift any month up.
Every station tells its own story: compare this curve with Spartanburg's pool season and Beaufort's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the South Carolina season index.
Sumter pool season FAQ
When should I open my pool in Sumter, SC?
Open by March 28 — the model places Sumter's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The Sumter opening guide has the 12-step sequence.
When should I close my pool in Sumter?
Close by October 30: cool water keeps its winter chemistry, but freeze damage is the hard stop. The Sumter closing guide sequences the work backward from that date.
How long is the swim season in Sumter?
Sumter averages 142 days a year with normal highs of 80°F or better — right on the statewide median. The South Carolina season index ranks all 12 covered cities by the same metric.
How warm does pool water get in Sumter?
An unheated pool near Sumter typically peaks around 80°F in high summer and bottoms out near 44°F in winter, spending roughly 2 months at or above the 78°F comfort line most swimmers prefer. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when Sumter hits the closing window
Data: NOAA 1991–2020 climate normals via Sumter (2.1 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.