LOS ANGELES, California — A wet and stormy setup is lining up for California and the Southwest this week, and our forecast team is watching it closely. Tropical moisture will fuel heavy downpours and thunderstorms from Tuesday night October 20 through Thursday October 22. That raises the risk of flash flooding and mudslides in cities like Los Angeles, San Diego, Las Vegas and Phoenix.
What Is Driving This Wet Setup
The main player is an upper-level low spinning just off the California coast. An upper-level low is a storm system high in the atmosphere that spins slowly and can sit in one place for days. As it turns, it pulls moisture from the south straight into the region.
That moisture is coming from the tropics, where warm, humid air is being pushed north toward Southern California and the desert. When that tropical air meets the cooler air from the storm, it creates the perfect setup for heavy rain and thunderstorms.
California Cities in the Path
Our latest forecast shows rain and storms spreading across much of California:
- Los Angeles and San Diego sit in the path of the tropical moisture moving in from the south, putting them at risk for heavy downpours.
- San Francisco is also inside the wet zone, with rain and storms expected during the event.
- Redding in Northern California falls inside the rain area as the storm spreads north.
- Medford and Bend farther north also sit near the wet zone as moisture spreads up the coast.
Flash Flood and Mudslide Risk
The biggest concern with this storm is flash flooding. Tropical moisture can produce very heavy rain in a short amount of time, and the ground cannot always soak it up fast enough. That water runs off quickly into streets, washes and low spots…