Pool season · South Dakota
Rapid City Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
This is the one-page view of Rapid City'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.
Rapid City, SD — 69 swim days a yearThe bar compresses Rapid City's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 13–June 3 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends September 29. Wherever the today marker sits, the nearest color change is your next appointment.
The Rapid City pool calendar
Opening — target May 20
Target May 20; the practical window runs May 13–June 3, and the 7-day mean crosses the 61°F threshold around June 3. Cold-water starts are the cheap ones.
Closing — deadline September 29
Hold the cover until September 19, then winterize by September 29, a week ahead of the October 8 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
This is Rapid City'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 27° | 26° | 32° | 41° | 50° | 61° | 70° | 73° | 68° | 55° | 42° | 32° |
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 Sioux Falls's pool season or jump back to the South Dakota season index to see the statewide spread.
Rapid City pool season FAQ
When should I open my pool in Rapid City, SD?
Open by May 20 — the model places Rapid City's 61°F crossing about two weeks later, and every warm day you wait pushes the water toward the 65°F algae zone. The Rapid City opening guide has the 12-step sequence.
When should I close my pool in Rapid City?
Close by September 29: cool water keeps its winter chemistry, but freeze damage is the hard stop. The Rapid City closing guide sequences the work backward from that date.
How long is the swim season in Rapid City?
Rapid City averages 69 days a year with normal highs of 80°F or better — right on the statewide median. The South Dakota season index ranks all 2 covered cities by the same metric.
How warm does pool water get in Rapid City?
An unheated pool near Rapid City typically peaks around 74°F in high summer and bottoms out near 26°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 Rapid City hits the closing window
Data: NOAA 1991–2020 climate normals via Rapid City Wfo (0.5 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.