Pool closing · Colorado
When to Close Your Pool in Lakewood, CO: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Plan to close your Lakewood pool by September 29. The local 7-day mean temperature drops out of the algae-risk zone around September 19, and NOAA normals put the first 32°F freeze near October 7 — winterize between those dates and the water goes under the cover cold, clean, and easy to reopen. Below: today's water estimate, the full closing window, and a step-by-step winterizing checklist.
Lakewood closing dates at a glance
| Closing window | September 19 – September 29 |
|---|---|
| Close by (deadline) | September 29 |
| First freeze, 50% probability | October 7 |
| Open by (recommended) | May 16 |
| Opening window | May 9 – May 30 |
| 61°F crossing (7-day mean) | May 30 |
| Swim-season length (80°F+ days) | 82 days |
| NOAA normals station | Lakewood · 3.5 mi · 5640 ft |
Lakewood banks only about 82 days of 80°F-plus afternoons — early opening weeks are the cheapest season extension available.
At roughly 5640 ft, Lakewood runs cooler than lowland forecasts for the same region — trust these local numbers over metro-wide weather graphics.
Put dates aside and follow the water: the Lakewood curve says roughly 46°F by mid-April, 65°F by mid-June, 72°F in mid-August, then back down through 53°F in mid-October. The summer ceiling sits near 73°F, and every window above is just a line drawn on this curve.
The 12-step Lakewood 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
Give the chemistry a head start — balance to label ranges several days out, while circulation can still mix corrections evenly. Closing-day dosing never distributes as well.
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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
Clean media goes into storage, dirty media comes out worse: backwash the sand or DE, rinse the cartridges, all per the manual, before anything drains.
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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
Check the cover manufacturer's spec before touching the hose: solid covers typically want water below the skimmer mouth, mesh often barely lower than normal. Full draining is off the table entirely.
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Blow out the lines and plug returns
The blowout is the whole ballgame: drive air through each line until it runs dry, seat the plug against the airflow, move to the next. A dry line cannot burst, full stop.
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Protect the skimmer
Install a skimmer guard bottle (or a plug rated for your skimmer) so ice that forms there crushes the sacrificial piece instead of cracking the skimmer body.
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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
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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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.
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Note this year's dates
Jot down when Lakewood's water actually cooled and when you closed. A two-line note beats memory next September 19 — your own yard runs a few days off any model, including ours.
What to buy before the rush
Every item below sells out somewhere in Colorado 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
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.
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Air pillow
Centers under the cover so ice pushes inward, not outward.
How Lakewood compares locally
Statewide context: across the 19 Colorado cities we model, Lakewood's September 29 deadline sits in the later half. Nearby, Arvada (9 mi) closes around September 28 and Westminster (13 mi) around October 4 — treat gaps under a week as microclimate noise, not strategy. Spring planning restarts at the opening guide; the Lakewood pool season page keeps the whole year in one view.
The instrument behind this page is Lakewood, 3.5 miles north of Lakewood — the closest station publishing complete 1991–2020 daily temperature normals. Thirty years of its readings set every date above; your own yard adds or subtracts a degree with shade, wind, and pavement, which is what the window's width is for.
Field notes for Lakewood owners
The warm spell after you closed
A 78°F week in October doesn't mean reopening. Water under an opaque cover warms far less than air suggests, and a closed, balanced pool tolerates a warm stretch fine. Check the cover pump has somewhere to send rain, enjoy the weather, and leave the plumbing sealed.
Salt cells overwinter indoors
Remove the cell at closing, inspect and clean per the manufacturer, and store it inside with the unions capped. A dummy cell or spacer keeps the plumbing sealed. Cells left in outdoor plumbing through freezes are a common — and completely avoidable — spring casualty.
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.
Closing for a real winter
A Lakewood 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.
Altitude closing notes
Elevation compresses Lakewood's closing window: at about 5640 ft, radiational cooling can drop a clear night below freezing while afternoons still feel like pool weather. Trust the first-freeze normal (October 7) over the vibe, stage the blowout gear early, and treat any clear-sky cold front in September as your cue.
Lakewood 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 Lakewood's actual water; the normals say the durable cool-down arrives near September 19, and anything inside the window to September 29 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 Lakewood, hold off until the cool-down near September 19 before covering.
Do I need antifreeze in pool lines?
Only where water might remain. If every line is properly blown out and plugged, air is the antifreeze. Lines you can't verify dry — long runs, low spots, water features — get pool-grade antifreeze dosed per its label. With Lakewood's first freeze normal near October 7, don't leave that question open.
How far should I drain my pool for winter?
Only to the line your cover manufacturer prints — a few inches below the skimmer for most solid covers, close to operating level for many mesh designs with the skimmer plugged. The water you leave in is structural: it holds the shell against groundwater all winter.
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. Lakewood 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 Lakewood?
September 29, by our model — the cool-down plus ten days (the freeze normal, October 7, 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 Lakewood's first freeze-risk stretch.
Email me when Lakewood hits the closing window
Data: NOAA 1991–2020 climate normals via Lakewood (3.5 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.