Rare September rain returns to Southern California following deadly flash flooding from Mario's remnants
This comes just a few days after the remnants of Tropical Storm Mario brought a surge of moisture into Southern California and parts of the Southwest, resulting in deadly flash flooding.
Rare September rain returns to Southern California, Southwest
An area of low pressure is setting up just off the coast of Southern California and will bring another round of unseasonable rain and potential flooding to the region, as well as parts of Arizona and the lower Colorado River Basin. While more rain is expected across the region beginning Monday, the highest potential for flash flooding in parts of Southern California will occur Tuesday and Wednesday.
SAN DIEGO – An area of low pressure is setting up just off the coast of Southern California and will bring another round of unseasonable rain and potential flooding to the region, as well as parts of Arizona and the lower Colorado River Basin.
This comes just a few days after the remnants of Tropical Storm Mario brought a surge of moisture into Southern California and parts of the Southwest, resulting in deadly flash flooding. Southern California, in particular, doesn't typically see much rain during September.
While more rain is expected across the region beginning Monday, the highest potential for flash flooding in parts of Southern California will occur Tuesday and Wednesday.
SAN FRANCISCO BAY AREA ROCKED BY MAGNITUDE 4.3 EARTHQUAKE MONDAY MORNING
(FOX Weather)
According to the FOX Forecast Center, a low-pressure system in the upper levels of the atmosphere has been cut off from the main jet stream, meaning that it has lost the traditional west-to-east movement of normal weather patterns. This so-called cutoff low is expected to stall off the coast, bringing days of rain to the region.
Similar to the weather pattern last week, this system is also drawing in tropical moisture from the remnants of a tropical system in the Pacific Ocean – Tropical Storm Narda.
This tropical moisture generally enhances the rain produced by any storms.
Car swept away in floodwaters in Barstow, California, on Sept. 18, 2025.
(Barstow Police Department)
Large amounts of rainfall in a short period of time caused flash flooding and debris flows in the hilly terrain of the San Bernardino mountains last week.
The floods claimed the life of a 2-year-old boy in Barstow, California, when the car he and his father were in was swept away Thursday evening. Rescue crews found the father alive, stranded on a makeshift island later that night, but his son's body wasn't found until Friday afternoon.
The San Bernardino County Fire Department said debris flows had left at least 10 people stranded on California State Route 38 last Wednesday night in the San Bernardino mountains. Fire officials said the stranded people were safe, and crews worked to clear the roadway.
The department said mudslides and debris flows had also impacted roads and homes in parts of Forest Falls, Oak Glen and Potato Canyon.
REMNANTS OF MARIO TRIGGER DEADLY FLASH FLOODING, MUDSLIDES AS RAIN SURGED ACROSS SOUTHERN CALIFORNIA
(FOX Weather)
The FOX Forecast Center said Monday's rain will be lighter, with intensity picking up on Tuesday. Another quarter- to half-inch of rain is possible on Tuesday on ground that is still saturated from last week.
NOAA's Weather Prediction Center has issued a Level 1 out of 4 risk of flash flooding for the California coast from San Jose to Santa Barbara Tuesday. The threat expands inland Wednesday to the Nevada border and farther south to parts of Los Angeles.
San Diego received 0.45 inches of rain during the last event, which is well above its average monthly rain for September – just 0.13 inches. This is now the city's seventh-wettest September to date.