Pool season · Colorado
Longmont Pool Season: the Year on One Bar
Last updated: July 15, 2026 · dates · water temp
This is the one-page view of Longmont'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.
Each dot on the bar is one week of Longmont's typical year, colored by what the model says that week is for: gray weeks are off-season, hollow teal marks the opening window (May 6–May 27), solid teal is swim season, and hollow amber is the closing window ending September 28. The black marker is today — its position against the colors is the entire executive summary.
The Longmont pool calendar
Opening — target May 13
Open by May 13 — a two-week head start on the May 27 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline September 28
Hold the cover until September 21, then winterize by September 28, a week ahead of the October 5 freeze normal. Late and cold beats early and warm.
Estimated water temperature by month
Monthly averages of the site's water model run on Longmont'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 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 29° | 30° | 37° | 45° | 52° | 63° | 71° | 72° | 68° | 56° | 44° | 33° |
The curve peaks near 73°F — comfortable-water months here usually involve a heater or a solar cover.
Email me when Longmont hits the closing window
Data: NOAA 1991–2020 climate normals via Longmont 2 ESE (1.2 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.