Pool closing · Washington
When to Close Your Pool in Bellevue, WA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Two dates decide a Bellevue closing: September 21, when the 7-day mean drops back through 61°F and the water goes algae-quiet, and October 1, the model deadline set a safe week ahead of the November 16 first-freeze normal. Everything on this page — live water estimate, window, winterizing sequence — exists to land you between them.
Bellevue closing dates at a glance
| Closing window | September 21 – October 1 |
|---|---|
| Close by (deadline) | October 1 |
| First freeze, 50% probability | November 16 |
| Open by (recommended) | May 24 |
| Opening window | May 17 – June 7 |
| 61°F crossing (7-day mean) | June 7 |
| Swim-season length (80°F+ days) | 0 days |
| NOAA normals station | Renton Municipal Airport · 7.6 mi · 29 ft |
Bellevue banks only about 0 days of 80°F-plus afternoons — early opening weeks are the cheapest season extension available.
The same model in water terms: Bellevue's estimated pool temperature runs about 50°F in mid-April, 61°F in mid-June, 68°F in mid-August, and 56°F in mid-October, peaking near 68°F. Those four checkpoints — not any calendar holiday — are what the windows above are protecting.
The 12-step Bellevue winterizing checklist
A closing is a plumbing project with a chemistry warm-up. Start a few days ahead of your target date, keep every dose per its product label, and don't skip the photographs — spring-you reassembles from them.
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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
Skim, brush walls and steps, and vacuum carefully. Any leaves or algae you seal under the cover become spring's chemistry problem, so closing day cleanliness pays twice.
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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
Run the winter kit through moving water: dose each product per its label with the pump on, give it a few hours to distribute, then start the shutdown. Chemistry added to still water stays where it lands.
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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
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
If any line can't be verified dry, add pool-grade antifreeze per its label. Use only pool antifreeze — automotive products don't belong 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
Center an inflated air pillow, then fit the cover and secure it with water bags, cable, or straps as designed. The pillow gives ice a place to push besides your walls.
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Note this year's dates
Jot down when Bellevue's water actually cooled and when you closed. A two-line note beats memory next September 21 — your own yard runs a few days off any model, including ours.
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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.
What to buy before the rush
Every item below sells out somewhere in Washington every September. Stocking the short list before the rush costs nothing extra and saves the mid-project store run — the chemicals guide explains what each category actually does.
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Winter cover
Sized to overlap; the cheapest insurance the pool wears all winter.
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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
Pool-rated glycol for the lines air couldn't clear.
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Winter closing kit
The under-the-cover chemistry, measured for your gallons.
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Air pillow
Gives ice somewhere to push besides your pool walls.
How Bellevue compares locally
Statewide context: across the 21 Washington cities we model, Bellevue's October 1 deadline sits in the earlier half. Nearby, Redmond (6 mi) closes around October 1 and Kirkland (7 mi) around October 1 — treat gaps under a week as microclimate noise, not strategy. Spring planning restarts at the opening guide; the Bellevue pool season page keeps the whole year in one view.
The measuring stick here is Renton Municipal Airport — 7.6 miles to the south, elevation about 29 feet. Its 1991–2020 record is what the model reads for Bellevue; your backyard in King 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 Bellevue owners
What comes indoors
Cartridges, the cover pump when idle, chemical containers, and anything with a small motor overwinter better in the garage. Cold cycling is hard on plastics and seals; shelf space is cheaper than replacements. Label a single bin now and spring assembly becomes a scavenger hunt with a map.
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.
The fifteen-minute monthly walk-around
Once a month all winter: pump or siphon standing water off solid covers, re-tension straps or top up water bags, confirm the level hasn't dropped enough to strand the cover, and glance at the pad for critter nests. Every major cover failure starts as a skipped walk-around.
Hard-winter homework
Where winter is long — Bellevue banks only about 0 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.
Bellevue 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 Bellevue's actual water; the normals say the durable cool-down arrives near September 21, and anything inside the window to October 1 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 Bellevue, hold off until the cool-down near September 21 before covering.
Do I need antifreeze in pool lines?
Blown-out, plugged lines don't need it; doubtful lines do. Use only antifreeze labeled for pools, at the label's rate per foot of pipe — never automotive antifreeze. In Bellevue the freeze clock starts around November 16, so settle this during closing, not during the first cold snap.
How far should I drain my pool for winter?
Follow the cover's instructions first: solid covers usually want water a few inches below the skimmer; some mesh setups run higher with the skimmer sealed. The hard rule is never empty — hydrostatic pressure can lift or crack an empty pool, a far worse outcome than any freeze.
What happens if you don't winterize a pool?
Two failure modes. Where freezes reach the plumbing, expansion cracks pumps, filters, and fittings from the inside. Where they don't, an unwatched pool simply drifts green and unbalanced by spring. Bellevue has no published freeze normal to pin the date, so the winterizing above plus forecast-watching covers both risks.
When is the last safe date to close in Bellevue?
Our model's practical deadline is October 1 — set by the cool-down plus ten days (the freeze normal, November 16, leaves room to spare). Push much past it and you're winterizing in freeze-warning weather, rushing the blowout, and hoping the cover goes on before the first hard night. Inside the September 21–October 1 window, none of that drama applies.
Email me when Bellevue hits the closing window
Data: NOAA 1991–2020 climate normals via Renton Municipal Airport (7.6 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.