Pool closing · California
When to Close Your Pool in Pomona, CA: Deadline, Window & Checklist
Last updated: July 15, 2026 · Model window year: 2026 · dates · checklist · FAQ
Circle November 23 on the Pomona 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 December 28. The window opens November 13 — the live widget below shows how this year is actually tracking against it.
Pomona closing dates at a glance
| Closing window | November 13 – November 23 |
|---|---|
| Close by (deadline) | November 23 |
| First freeze, 50% probability | December 28 |
| Open by (recommended) | March 14 |
| Opening window | March 7 – March 28 |
| 61°F crossing (7-day mean) | March 28 |
| Swim-season length (80°F+ days) | 144 days |
| NOAA normals station | Pomona/fairplex · 1.6 mi · 999 ft |
Pomona's 144-day warm season leaves comfortable margins on both ends — the windows above aim you at the cheap-chemistry versions of each transition.
Four water checkpoints anchor Pomona's year in the model: mid-April at about 62°F, mid-June at 70°F, mid-August near the 78°F peak zone, and mid-October easing through 69°F. The dates in the table are where those numbers cross the thresholds that matter.
The 12-step Pomona 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
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
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
Drop the level as your cover manufacturer specifies — typically below the skimmer mouth for solid covers. Never drain a pool fully; groundwater pressure can damage the shell.
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Blow out the lines and plug returns
Work line by line: push air until the return spits dry mist, plug it against the flowing air, move on. Skimmer, returns, cleaner line, in whatever order your plumbing prefers — dry pipes are the entire point of closing.
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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 the drains on everything that holds water and let the pad empty completely. Cartridges and small equipment overwinter far better on a garage shelf than outside.
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Set the air pillow and cover
Pillow first, cover second, tension last. A properly centered pillow turns the winter ice sheet from a wall-pressing ram into a harmless dome.
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Note this year's dates
Jot down when Pomona's water actually cooled and when you closed. A two-line note beats memory next November 13 — 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
The November crowd empties shelves in a predictable order. This is the short list worth owning before Pomona's window opens — nothing exotic, just the stuff everyone needs the same weekend.
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Expansion plugs + skimmer guard
The blowout's finishing move — one per return, one for the skimmer.
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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
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
Keeps rain and melt off a solid cover all season.
How Pomona compares locally
Statewide context: across the 147 California cities we model, Pomona's November 23 deadline sits in the earliest quarter. Nearby, Upland (7 mi) closes around November 28 and Chino (8 mi) around November 24 — treat gaps under a week as microclimate noise, not strategy. Spring planning restarts at the opening guide; the Pomona pool season page keeps the whole year in one view.
Every number on this page traces to one instrument cluster: Pomona/fairplex, 1.6 miles north of Pomona's center at an elevation near 999 feet. NOAA computed its 1991–2020 normals from roughly three decades of daily readings — long enough that one strange spring in Los Angeles County barely moves the dates.
Field notes for Pomona owners
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.
Cold water is the whole point
A pool closed at 55°F barely changes all winter: algae are dormant, chemicals hold, and spring opens with a light dusting instead of a bloom. A pool closed at 72°F runs its own quiet ecosystem under the cover for a month. The date matters less than the water temperature it represents.
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.
Pomona 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 Pomona's actual water; the normals say the durable cool-down arrives near November 13, and anything inside the window to November 23 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 Pomona, hold off until the cool-down near November 13 before covering.
Do I need antifreeze in pool lines?
Treat antifreeze as a backup, not a substitute: the real protection is air in dry lines. Where a full blowout isn't possible, pool-grade antifreeze per label is cheap insurance against a cracked pipe — worth it anywhere freezes are routine, and Pomona sees them from about December 28.
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?
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. Pomona reaches freeze territory around December 28 — the checklist above is cheaper than any one of those repairs.
When is the last safe date to close in Pomona?
Our model's practical deadline is November 23 — set by the cool-down plus ten days (the freeze normal, December 28, 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 November 13–November 23 window, none of that drama applies.
Email me when Pomona hits the closing window
Data: NOAA 1991–2020 climate normals via Pomona/fairplex (1.6 mi); live outlook by Open-Meteo. Full attribution on the sources page. Model assumptions and error bars on methodology.