Pool season · Iowa
Sioux City Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
This is the one-page view of Sioux 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.
Sioux City, IA — 90 swim days a yearReading it takes ten seconds: 52 dots, one per week. Solid teal is Sioux City's swim season; the hollow teal run before it (April 29 to May 20) is when to open; the hollow amber run after is when to close, with September 30 as the deadline; gray is the covered season. Today's marker shows where you stand in that cycle right now.
The Sioux City pool calendar
Opening — target May 6
Open by May 6 — a two-week head start on the May 20 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline September 30
Hold the cover until September 24, then winterize by September 30, a week ahead of the October 7 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on Sioux 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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 20° | 21° | 30° | 43° | 54° | 66° | 73° | 74° | 68° | 58° | 42° | 29° |
The curve peaks near 75°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Iowa City's pool season and Waterloo's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the Iowa season index.
Sioux City pool season FAQ
When should I open my pool in Sioux City, IA?
Open by May 6 — the model places Sioux 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 Sioux City opening guide has the 12-step sequence.
When should I close my pool in Sioux City?
Close by September 30: cool water keeps its winter chemistry, but freeze damage is the hard stop. The Sioux City closing guide sequences the work backward from that date.
How long is the swim season in Sioux City?
Sioux City averages 90 days a year with normal highs of 80°F or better — about 5 days later than the Iowa median. The Iowa season index ranks all 6 covered cities by the same metric.
How warm does pool water get in Sioux City?
An unheated pool near Sioux City typically peaks around 75°F in high summer and bottoms out near 19°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 Sioux City hits the closing window
Data: NOAA 1991–2020 climate normals via Sioux City Ang (6.9 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.