An unusual weather pattern for July is bringing a chance of dry lightning and scattered showers to parts of Southern California this weekend, which has raised the risk for fire starts, flash flooding and debris flows, the National Weather Service said.
The early monsoonal moisture brought showers and storms across Orange County and the Inland Empire late Thursday and into early Friday, with the system moving toward the Los Angeles, Ventura and San Bernardino county mountains by Friday afternoon, according to the National Weather Service. Thunderstorms were most likely to hit the the San Gabriel Mountains and foothills and the Antelope Valley in Los Angeles County. Storms were also expected across the San Bernardino County mountains and surrounding high desert.
As of Friday afternoon, the weather service had issued flash flood warnings for Lake Arrowhead, Blue Jay, Cedar Glen, Big Bear Lake and Arrowbear Lake in the San Bernardino Mountains, warning of “life-threatening flash flooding of creeks and streams, urban areas, highways, streets and underpasses.” In parts of those mountainous areas — popular for summer outdoor adventures — forecasters expected rainfall rates up to and over an inch of rain per hour, likely to cause localized flooding for a brief period through 4 p.m.
“Turn around, don`t drown when encountering flooded roads,” the weather service warned. “In hilly terrain there are hundreds of low water crossings which are potentially dangerous in heavy rain. … Move away from recently burned areas. Life-threatening flooding of creeks, roads and normally dry arroyos is likely. The heavy rains will likely trigger rockslides, mudslides and debris flows in steep terrain, especially in and around these areas.”
Depending on the strength of the rain pockets and thunderstorms, the weather service warned other areas could also see localized flooding and strong winds. In certain burn scars, particularly the footprints of the 2024 Bridge fire that burned near Wrightwood and the Eaton fire in and around Altadena, there’s an elevated risk for “more significant debris flows,” the weather service warned.
“We’re going to keep a close eye on things,” said Joe Sirard, a meteorologist with the weather service’s Oxnard office.
Sirard said those storms also bring with them the possibility of wildfires.
“There is dry lightning potential,” Sirard said. “Sometimes you might get a rain shaft with lightning, but the lightning can occur and strike outside of the rain shaft.”
Sirard said the conditions driving the rare thunderstorms aren’t the typical summer monsoonal pattern in which moisture flows from the desert southwest into Southern California. Rather, this one is fueled by a low-pressure system in northern Mexico pulling air south, creating similar outcomes.
“Any time during the summer when we get moisture at mid-levels in the atmosphere and some mechanism to help destabilize the atmosphere … [there’s a] slight chance of showers and thunderstorms,” Sirard said.
