Southern California rain doesn’t drizzle in politely — it stays away for six months and then arrives all at once. That schedule is exactly why the first storm of the season is when windows fail. Caulking that baked all summer, weep holes packed with dust, weatherstripping flattened by a hundred-degree August: none of it announces a problem until water is running down the inside of the glass. A little time spent now to prep windows for rain saves a wet windowsill — or a stained ceiling — in November.
We’ve been repairing windows across Glendora, La Verne, San Dimas, Claremont, Covina, Azusa, Pomona, and Upland since 1989 — 36 years, family owned — and every fall the phone rings the morning after the first real storm. Almost everything those calls describe was findable in September. Here’s the walk-around we’d do at our own houses, in roughly the order we’d do it.
The short version
Walk the outside of the house and check four things at every window: the caulking, the weep holes, the weatherstripping, and the glass itself. Anything cracked, crumbling, clogged, or fogged goes on a list — and that list gets handled before the forecast turns. If you’d rather hand us the list, request a free estimate or call (626) 335-2900.
Why SoCal rain is harder on windows than it sounds
Our rain pattern is feast or famine. The San Gabriel Valley can go from bone dry to several inches in a single atmospheric-river weekend, which means windows here face a stress test instead of a steady drizzle. Wind-driven rain hits vertical glass and stucco for hours, finds every gap summer opened up, and keeps feeding water into it faster than the wall can dry out.
Summer is what opens those gaps. Months of heat and UV shrink and crack exterior caulk, dry out vinyl weatherstripping, and warp the fins on older screens. If you read our guide to prepping windows and screens for Santa Ana season, the logic is the same — the dry season does the damage quietly, and the first weather event sends the bill.
How to prep windows for rain: the 20-minute walk-around
Pick a cool morning, take your phone for photos, and walk the exterior one window at a time. You’re looking at four things per window.
1. Check the caulking where frame meets stucco
Run your eye — and a fingertip — along the bead where the window frame meets the wall. Fresh caulk is flexible and unbroken. Failed caulk is chalky, cracked like dry lakebed, or pulling away from one side of the joint. Hairline gaps matter more than they look: wind-driven rain moves sideways, and a gap the width of a credit-card edge will pass water for hours. Small runs are a straightforward re-caulk; if the bead is failing on every window, have it done in one pass so it all ages together.
2. Find and clear the weep holes
Sliders and most vinyl windows drain through small slots at the bottom of the exterior frame — weep holes. Their whole job is to let rain that gets into the track escape outside. After a dusty SGV summer they’re often packed with dirt, cottonwood fluff, or stucco debris, and a blocked weep hole turns the window track into a bathtub that overflows into the house. Clear them gently with a zip tie or pipe cleaner (nothing sharp — there’s a baffle inside), then pour a little water into the track and watch that it drains out the front.
3. Press-test the weatherstripping
Open each window and look at the pile or bulb seal around the sash. It should spring back when pressed. If it’s flattened, brittle, or detached at the corners, air and water both have a path in — the same failure that makes rooms drafty in January. While you’re there, confirm the window still opens and closes without a fight; a sash that binds usually isn’t sealing either. Our guide to freeing a stuck window covers the safe fixes.
4. Look at the glass itself
Two things disqualify glass from facing a storm. The first is any crack or chip — glass flexes under wind load, and a cracked pane can finish failing mid-storm. Our walkthrough on what to do before a broken-window repair covers how to stabilize one safely until it’s replaced. The second is fog or a milky haze between the panes of a dual-pane unit: that’s a failed seal, and cool, damp mornings will make it dramatically worse. Here’s how to tell whether a foggy dual-pane unit is repairable.
What you find vs. what it means
| What you see | What it usually means | The fix |
|---|---|---|
| Cracked, chalky caulk at the frame edge | Sun-baked sealant has failed | Cut out and re-caulk the joint |
| Water pooling in the track | Blocked weep holes | Clear the weeps; verify drainage |
| Flattened or brittle sash seals | Worn weatherstripping | Replace the pile or bulb seal |
| Fog or minerals between panes | Failed insulated-glass seal | Replace the glass unit, not the window |
| Crack or chip anywhere in the pane | Glass can fail under wind load | Tape, photograph, and schedule glass replacement |
Don’t forget sliders, tracks, and screens
Patio doors deserve their own minute. Vacuum the track, check the weeps at each end, and roll the panel slowly — grinding or dragging means the rollers are wearing, and a door that won’t seat squarely in its jamb won’t seal against wind either. (Rollers are a cheap fix; here’s how sliding door roller repair works.)
Screens don’t keep rain out, but rain season is still when they take damage. Check that frames sit tight in their openings so gusts can’t peel them off, and pull screens from any window you plan to leave cracked open for fresh air — a loose screen flapping against wet glass all winter does neither any good. If the mesh is torn or the frames are racked out of square, our screen shop builds replacements to measure.
Inside the house: condensation season is coming
The first cool, wet week is also when winter condensation shows up — and it fools a lot of homeowners into thinking the window is leaking. Water beading on the room side of the glass is indoor humidity meeting cold glass, not storm water getting in. It matters where the moisture sits, though, because it can pool on sills and feed mildew in the corners. Our guide to window condensation — inside, outside, or between the panes explains how to read each kind and when it signals a real problem.
When to book the repair (hint: not the week of the storm)
Every glass shop in the valley gets busy the same week — the one right after the first storm. Book in early fall and a re-caulk, seal replacement, or window repair is quick to schedule; call during a storm run and you’ll wait behind everyone whose window announced itself the hard way. Insulated-glass units are also built to order, so a foggy-unit replacement carries fabrication time you want on the calendar before the weather turns.
And if the walk-around turns up a window that’s failing on every count — seals, hardware, glass, and frame — rain season is a sensible deadline for a bigger decision. Our guide to the seven signs it’s time to replace a window can help you make that call with a clear head. We handle both sides of that line every week for homeowners from Glendora to Upland.
Quick answers
Do I need to caulk my windows every year?
No. A good exterior bead lasts years. What’s worth doing every year is the five-second inspection — sun exposure varies wall to wall, so south- and west-facing windows in our climate usually fail first while the north side is still fine.
Why does water pool in my window track when it rains?
Usually blocked weep holes, and some pooling is normal by design — tracks catch water and drain it out the front. It’s a problem when the water rises instead of draining, which means the weeps are clogged or the frame has settled out of level.
Is rain getting between my window panes?
No — moisture between the panes is condensation from a failed factory seal, not rain getting in. Rain just makes it visible sooner. The insulated glass unit can typically be replaced without replacing the whole window frame.
The bottom line
Prepping windows for rain is a 20-minute walk and four checks per window: caulk, weeps, weatherstripping, glass. Fix the small stuff yourself, list the rest, and get it scheduled while the sky is still blue.
Or hand us the walk-around entirely. Glendora Window has kept San Gabriel Valley weather on the right side of the glass since 1989 — 4.8 stars across 160+ verified reviews and 50,000+ jobs completed. Request a free estimate or call (626) 335-2900 and we’ll have you ready before the first storm shows up on the forecast.
