A powerful storm is currently strengthening over Southern California, and while that sounds like just another rainy day, there is some serious science making this one particularly dangerous.
Conditions are expected to rapidly deteriorate over the coming hours. Right now, the atmosphere is shifting from providing a beneficial rain to posing a genuine flood hazard. As significant moisture surges toward the California coast, the rain amounts and intensities will increase through the day.
The biggest concern isn’t just how much rain falls, but how fast it comes down. We are expecting rates of 0.5 to 0.75 inches per hour, with some spots seeing up to 1 inch locally.
Anything over 0.30 inches per hour is considered “heavy” rain. A rate of 1 inch per hour is intense enough to overwhelm storm drains and fill neighborhood streets faster than they can drain.
The storm is slamming into the Transverse Ranges—mountain chains like the San Gabriels and Santa Monicas that run east-to-west. When moist air hits these mountains, it is forced upward in a process called orographic lift. This acts like “wringing out a sponge,” causing much heavier rain on the mountain slopes than at the coast. This is why mountain areas could see 3–5 inches of total rain today while coastal areas see 1–2 inches.
If you live near an area recently hit by wildfires, like the Sunset or Palisades fire zones, you are at the highest risk. Burned soil becomes water-repellant, acting more like pavement than dirt.
It only takes about 0.5 inches of rain in an hour to trigger a debris flow—a fast-moving landslide of mud, rocks, and trees. These are unpredictable and can move faster than a person can run.
The worst of the rain and the peak flash flood risk are expected to reach the Los Angeles Metro area after 10:00 a.m. PT and linger into early Tuesday.
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