Flooding from post-tropical Mario prompts water rescues, mud and debris flows in San Bernardino County, California
Remnants of Tropical Storm Mario brought widespread rainfall to California and the Desert Southwest on September 17 and 18, 2025, prompting water rescues, triggering mudslides, and flash flooding across the region.
Mudflow near Yucaipa, San Bernandino County, California on September 18, 2025. Credit: CAL FIRE San Bernardino/Inyo/Mono Unit
Moisture from the remnants of Tropical Storm Mario reached California and parts of the Desert Southwest on September 17, producing heavy rainfall that led to flash flooding, mudslides, and debris flows.
The National Weather Service (NWS) placed more than 7 million people under flood watches across Southern California and neighboring states, citing particular concern for mountainous regions and burn-scarred slopes vulnerable to debris flows.
In California’s San Bernardino County, flooding on September 18 prompted water rescues, including one in the area of Boulder Avenue and Baseline Street in the City of Highland.
Mudslides and downed power lines were reported near Yucaipa, while in nearby Oak Glen, mud and debris flow caused the closure of Oak Glen Road from Chagall to Potato Canyon. In Kern County, vehicles were trapped in mud on Highway 14.
Rainfall totals over the past 48 hours have ranged from 1 mm (0.05 inches) to 5 mm (0.20 inches), with many foothill and mountain areas recording up to 13 mm (0.50 inches), meteorologists at NWS Los Angeles/Oxnard said at 23:20 PDT on September 18 (06:20 UTC, September 19).
The Flood Watch for northern Ventura County and northern portions of Los Angeles County has been allowed to expire as more intense thunderstorm and shower activity ended by the end of September 18.
Rainfall totals in San Diego County coastal areas reached up to 15 mm (0.58 inches), with most sites reporting between 8 and 13 mm (0.30 to 0.52 inches).
In the San Bernardino County mountains, totals peaked at 68 mm (2.68 inches) in Fawnskin, 58 mm (2.30 inches) in Forest Falls, and 53 mm (2.09 inches) at Big Bear Lake Dam, NWS San Diego reported at 18:18 PDT on September 18 (01:18 UTC, September 19).
In Riverside County mountains, Snow Creek near Idyllwild recorded 68 mm (2.68 inches), Tick Ridge 46 mm (1.81 inches), and Mount San Jacinto 44 mm (1.73 inches).
The San Diego County desert region reported some of the heaviest totals in the area, including 44 mm (1.72 inches) at Borrego Palm Canyon and 36 mm (1.43 inches) at Coyote Creek.
In Coachella Valley, the highest amounts included 37 mm (1.46 inches) at Whitewater Trout Farm and 23 mm (0.91 inches) at Agave Hill, while Morongo Valley received 22 mm (0.87 inches).
Lingering moisture and remnant energy from former Tropical Storm Mario will continue to bring heavy rain to parts of California, the Great Basin, and the Southwest on Friday, September 19.
An isolated threat of flash flooding existed along higher terrain from California’s central valleys eastward through the central Great Basin and into the Southwest.
NWS noted a more concentrated threat in the central Sierra Nevada, where upslope flow enhanced rainfall. A Slight Risk of Excessive Rainfall (level 2 of 4) was in effect.
Heavier rainfall and the flash flood threat were expected to subside into the evening hours. On Saturday, storm chances are forecast to shift northward from the northern Great Basin into the central Rockies, while lingering in the Southwest. However, the storms are expected to be more scattered with lighter rainfall totals.
Despite the widespread precipitation, meteorologists noted that the event will not provide significant long-term drought relief. While the moisture is beneficial in the short term, it is insufficient to reverse persistent dry conditions across the Southwest.
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
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