Pool closing · Washington
When to Close Your Pool in Olympia, WA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Circle September 18 on the Olympia 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 14. The window opens September 8 — the live widget below shows how this year is actually tracking against it.
Olympia closing dates at a glance
| Closing window | September 8 – September 18 |
|---|---|
| Close by (deadline) | September 18 |
| First freeze, 50% probability | October 14 |
| Open by (recommended) | June 14 |
| Opening window | June 7 – June 28 |
| 61°F crossing (7-day mean) | June 28 |
| Swim-season length (80°F+ days) | 0 days |
| NOAA normals station | Olympia Airport · 4.7 mi · 188 ft |
A short season cuts both ways: every week opened before June 28 is a real slice of Olympia's roughly 0-day warm-swim budget.
Put dates aside and follow the water: the Olympia curve says roughly 47°F by mid-April, 58°F by mid-June, 65°F in mid-August, then back down through 52°F in mid-October. The summer ceiling sits near 65°F, and every window above is just a line drawn on this curve.
The 12-step Olympia winterizing checklist
The order matters more than the date: balanced water first, verified-dry lines before anything else freezes-proofs, and the cover only after everything below it is done. Work the list inside the window above.
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Balance the water a few days ahead
Start midweek for a weekend close: bring alkalinity and pH into their label ranges and let the water settle. What you seal under the cover is what the pool soaks in until spring.
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Deep-clean the pool
Brush, skim, and vacuum like company's coming. A pool that goes under the cover spotless comes out needing a rinse; one that goes under dirty comes out needing a project.
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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
Winter chemicals go in before shutdown, not after: label-dosed, circulated for a few hours, distributed evenly. A floater dropped on still water protects one corner.
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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
Push air through skimmer, return, and cleaner lines until they run dry mist, then seat expansion plugs at each return while air still flows. This is the single most important freeze-protection step.
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Protect the skimmer
Seat a skimmer guard or bottle in the throat — ice that forms there needs a sacrifice, and a two-dollar bottle beats a plumbing repair under the deck.
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Add pool antifreeze where blowouts fall short
Any line you can't prove is dry gets pool-grade antifreeze at the label's rate per foot. Automotive antifreeze is toxic in this context — pool-rated only, always.
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Drain the equipment
Every vessel on the pad — pump, filter, heater, chlorinator — gets its drain plugs pulled. Drop all the plugs in the pump basket; that's the one place everyone looks first in spring.
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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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Shut down the heater carefully
Follow the manufacturer's winterizing sequence for your heater — drain it fully and, for gas units, close the supply valve. Heat exchangers are the most expensive freeze casualty on the pad.
What to buy before the rush
The September crowd empties shelves in a predictable order. This is the short list worth owning before Olympia's window opens — nothing exotic, just the stuff everyone needs the same weekend.
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Winter closing kit
Closing chemistry in one box, dosed by pool volume.
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Air pillow
Centers under the cover so ice pushes inward, not outward.
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Winter cover
The one purchase every other closing step depends on.
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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.
How Olympia compares locally
Two nearby data points to triangulate with: Tacoma, 25 miles from Olympia, models its close at September 29 (roughly two weeks later); Federal Way, 32 miles out, at September 29. Olympia's own window ends September 18. For the other half of the calendar see when to open in Olympia, or scan the full year on the season page.
Local means local: Olympia's dates come from Olympia Airport, the nearest station with complete daily temperature normals — 4.7 miles south, about 188 feet up. Between that station and a Thurston County backyard there's always a degree or two of microclimate; the windows are built wide enough to carry it.
Field notes for Olympia owners
Cover pumps die in the cold — plan for it
A cover pump left running into a hard freeze can lock in ice and burn out. On freezing forecasts, pull it, let the storm pass, and put it back for the melt. Automatic models with freeze protection earn their price in exactly one forgotten weekend.
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.
The mesh-cover spring surprise, prevented in fall
Mesh-covered pools green up early because late-winter sun plus nutrient-carrying meltwater reaches the water. The fall counter-moves: close late and cold, dose the winter kit exactly per label, and plan an early-spring peek under the cover rather than a Memorial Day reveal.
Closing for a real winter
A Olympia closing has to hold for months of freeze-thaw, not a few frosty mornings. Spend the effort where winters bite: prove every line dry, drain every vessel on the pad, guard the skimmer, and tension the cover for wind that will actually come. The reward is a spring opening that's a rinse, not a rebuild.
Olympia pool closing FAQ
What temperature should water be to close a pool?
Cold enough that biology has clocked out — below 65°F and falling, ideally low 60s. The widget above tracks Olympia's actual water; the normals say the durable cool-down arrives near September 8, and anything inside the window to September 18 closes clean.
Can you close a pool too early?
Yes — it's the most common closing mistake. Seal 70°F water under a cover and algae keep growing in the dark all autumn; the spring opening turns green and expensive. In Olympia, hold off until the cool-down near September 8 before covering.
Do I need antifreeze in pool lines?
It depends entirely on your confidence in the blowout. Lines that blew fully dry need nothing; anything uncertain — low runs, water features, a stubborn cleaner line — gets pool-grade antifreeze at the label's rate per foot. With Olympia's freeze clock starting near October 14, uncertainty is the thing to eliminate.
How far should I drain my pool for winter?
As far as your cover manufacturer specifies and no farther — typically a few inches below the skimmer mouth for solid covers, near normal level for many mesh systems with skimmer plugs. Never drain fully: an empty shell can shift or crack under groundwater pressure.
What happens if you don't winterize a pool?
In a freeze climate, physics wins: water expands about 9% when it freezes, cracking pump housings, filter tanks, heat exchangers, and pipes. With Olympia's first 32°F night arriving near October 14 in the normals, an unwinterized pad is a spring repair bill waiting to be discovered.
When is the last safe date to close in Olympia?
September 18, by our model — the cool-down plus ten days (the freeze normal, October 14, leaves room to spare). Later closes happen, but they happen in gloves. The winterizing steps above take a weekend; leave yourself at least that much runway before Olympia's first freeze-risk stretch.
Email me when Olympia hits the closing window
Data: NOAA 1991–2020 climate normals via Olympia Airport (4.7 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.