Pool closing · Wyoming
When to Close Your Pool in Cheyenne, WY: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Circle September 20 on the Cheyenne calendar. Closing earlier traps warm, algae-friendly water under the cover; closing later gambles the plumbing against the first freeze, which the 1991–2020 normals place near October 1. The window opens September 10 — the live widget below shows how this year is actually tracking against it.
Cheyenne closing dates at a glance
| Closing window | September 10 – September 20 |
|---|---|
| Close by (deadline) | September 20 |
| First freeze, 50% probability | October 1 |
| Open by (recommended) | May 28 |
| Opening window | May 21 – June 11 |
| 61°F crossing (7-day mean) | June 11 |
| Swim-season length (80°F+ days) | 58 days |
| NOAA normals station | Cheyenne Wfo · 1.4 mi · 6119 ft |
A short season cuts both ways: every week opened before June 11 is a real slice of Cheyenne's roughly 58-day warm-swim budget.
Elevation caveat: Cheyenne's station sits near 6119 ft, where clear-night cooling outpaces valley forecasts; the local normals above already reflect that.
Four water checkpoints anchor Cheyenne's year in the model: mid-April at about 41°F, mid-June at 61°F, mid-August near the 68°F peak zone, and mid-October easing through 49°F. The dates in the table are where those numbers cross the thresholds that matter.
The 12-step Cheyenne winterizing checklist
Sequenced against Cheyenne's September 10–September 20 window: chemistry while the pump still runs, blowouts before the equipment drains, cover last. Labels dictate every dose.
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Balance the water a few days ahead
Three or four days before closing, adjust alkalinity and pH into label ranges. Balanced water is gentler on the liner, plaster, and equipment through the long covered months ahead.
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Deep-clean the pool
Make the last cleaning the best one of the year: full skim, full brush, careful vacuum. Debris left behind steeps all winter and greets you as April's water problem.
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Service the filter one last time
One final filter service per the manual — cartridges rinsed and stored dry indoors, sand or DE backwashed. Winter turns trapped gunk into concrete.
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Apply winter chemicals per label
Add a winterizing kit or your usual closing chemicals exactly as their labels direct for your volume, with the pump still circulating so everything distributes before shutdown.
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Lower the water level
Take the level down only as far as the cover's manual says — usually just below the skimmer for solid covers, higher for many mesh systems. An empty pool is never the goal; shells crack and shift without water's weight.
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Blow out the lines and plug returns
Air through every line — skimmer, returns, cleaner — until each blows dry mist, plugging returns while the air still pushes. Nothing else on this list protects as much plumbing per minute.
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Protect the skimmer
The skimmer throat is where trapped water has no escape — park a guard bottle or rated plug in it and let ice crush the cheap part.
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Add pool antifreeze where blowouts fall short
Doubt is the criterion: any run you can't confirm dry gets pool-grade antifreeze at the label's per-foot rate. The automotive jug from the garage is for cars — it has no business in pool plumbing.
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Drain the equipment
Open every drain plug on the pump, filter, heater, and chlorinator, and store the plugs in the pump basket so spring reassembly is a one-stop hunt. Move what you can indoors.
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Set the air pillow and cover
Float a centered air pillow, then land the cover and secure it the way its design intends — bags, cable, or straps. Ice sheets need somewhere to collapse inward, and the pillow is that somewhere.
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Remove and store ladders and rails
Pull ladders, rails, and the diving-board hardware; rinse, dry, and store them out of the weather. Anchor sockets get a dab of protectant so spring bolts turn freely.
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Note this year's dates
Jot down when Cheyenne's water actually cooled and when you closed. A two-line note beats memory next September 10 — your own yard runs a few days off any model, including ours.
What to buy before the rush
A small stack of supplies turns the checklist above into a single-weekend job. Buy before Cheyenne's September rush and the whole list ships at leisure instead of sprinting.
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Air pillow
A soft target for the ice sheet, centered under the cover.
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Winter cover
Measure with overlap; the winter workhorse over everything else.
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Cover pump
Standing water is a cover killer; this is the counter.
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Expansion plugs + skimmer guard
Cheap rubber that stands between ice and your fittings.
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Pool antifreeze
Backup for unverifiable lines; label rate per foot of pipe.
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Winter closing kit
Season-length winter chemicals in one label-dosed box.
How Cheyenne compares locally
Cheyenne closes in the earlier half of Wyoming's calendar. Neighbors run close: Fort Collins (43 mi away) models its deadline at September 30 (about a week later vs Cheyenne's September 20), while Greeley (50 mi) shows October 1. The spring mirror of this page is the Cheyenne opening guide, and the season overview draws both windows on a single bar.
The measuring stick here is Cheyenne Wfo — 1.4 miles to the northwest, elevation about 6119 feet. Its 1991–2020 record is what the model reads for Cheyenne; your backyard in Laramie County will run a touch warmer or cooler with shade, wind, and pavement, which is exactly the slack the two-week lead absorbs.
Field notes for Cheyenne owners
Match the drainage plan to the cover
Solid covers shed nothing — they need a cover pump staged before the first storm and checked after each one. Mesh covers drain themselves but pass silt that settles all winter. Either way, the plan is decided in October, not improvised in January when the cover is an ice sheet.
Gas heaters get the manual, not a guess
Every heater brand sequences its winterizing differently — drain plugs, blower considerations, gas supply, control settings. The generic advice (drain fully, close the valve) is right but incomplete; ten minutes with your model's manual protects the most expensive component you'll winterize.
Leaf season vs closing day
If your yard drops serious leaves, the cheap trick is a leaf net over the main cover through the drop, then one bulk removal before snow. Leaves that winter on (or worse, under) the cover steep like tea and hand you stained water and clogged pumps in spring.
Hard-winter homework
Where winter is long — Cheyenne banks only about 58 warm-swim days — the closing carries months of load. Bury the effort where it counts: verified-dry lines, fully drained equipment, a skimmer guard, and a cover secured for real wind. A short season forgives a late opening; it never forgives a cracked pump.
Altitude closing notes
Elevation compresses Cheyenne's closing window: at about 6119 ft, radiational cooling can drop a clear night below freezing while afternoons still feel like pool weather. Trust the first-freeze normal (October 1) over the vibe, stage the blowout gear early, and treat any clear-sky cold front in September as your cue.
Cheyenne pool closing FAQ
What temperature should water be to close a pool?
Below roughly 65°F, and trending down. Water closed warm keeps feeding algae under the cover for weeks; water closed in the 50s goes dormant almost immediately. Cheyenne's cool-down lands near September 10 in the normals, which is why the window opens there.
Can you close a pool too early?
You can, and warm-water closings are why "we opened to a swamp" stories exist. The fix is patience: let Cheyenne's water cool through the mid-60s°F — around September 10 by our model — then close inside the window that ends September 20.
Do I need antifreeze in pool lines?
Only for lines you can't verify dry — a proper blowout makes antifreeze unnecessary. Where doubt remains, use pool-grade product at its label rate, never automotive. No freeze-probability normal is published near Cheyenne, so let the live forecast, not a calendar, tell you when freeze protection starts mattering.
How far should I drain my pool for winter?
Less than most people think. Below the skimmer opening is the classic solid-cover target; mesh covers often specify higher water. The cover's own manual wins every argument, and "drain it completely" is never the answer — empty shells pop out of wet ground.
What happens if you don't winterize a pool?
The freeze finds every shortcut. Ice in an unprotected pump or heater cracks castings from the inside; ice in underground lines splits fittings you can't see until spring. Cheyenne reaches freeze territory around October 1 — the checklist above is cheaper than any one of those repairs.
When is the last safe date to close in Cheyenne?
The model draws the line at September 20 for Cheyenne. It isn't arbitrary: the cool-down plus ten days (the freeze normal, October 1, leaves room to spare), and the whole closing sequence needs a working weekend of margin. The one exception that overrides any date — a hard freeze inside the 10-day forecast, which the widget above flags as urgent.
Email me when Cheyenne hits the closing window
Data: NOAA 1991–2020 climate normals via Cheyenne Wfo (1.4 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.