Southern California’s summer rains explained
The North American monsoon brings sticky, tropical weather to Los Angeles and showers and thunderstorms mostly to Southern California’s mountains and deserts. Here’s how it works:
1. Late spring and early summer
The subtropical ridge of high pressure is typically over Mexico.
2. July through September
High pressure shifts to the north and expands, bringing heat to the desert Southwest and Southern California.
3. Monsoonal moisture
Clockwise circulation around the high pressure pulls subtropical moisture up from the south.
4. Summer showers and thunderstorms
Monsoonal showers and thunderstorms sometimes spill over from the mountains and deserts into the L.A. Basin.
Sources: Bill Patzert, NASA Jet Propulsion Laboratory; National Weather Service Los Angeles/Oxnard; AccuWeather; Times reporting