Thunder, lightning and spells of intense rain moved through west San Bernardino and Riverside counties before sunrise Monday, and more storms were possible near the Cajon and San Gorgonio passes later in the day, a National Weather Service meteorologist said.
More storms Monday afternoon could be a concern in the San Jacinto Mountains, where recent fires left more than 70 square miles of watershed vulnerable to post-fire erosion, flash flooding and debris flows.
They could also impact the Cleghorn and Inspiration burn areas near the 15 Freeway in Cajon Pass and State Route 18 in Waterman Canyon.
"We've got isolated storms this morning," Greg Martin of the Weather Service in San Diego said in a phone interview before 6 a.m. "The primary concern this afternoon will more activity over the San Bernardino mountains and desert areas.
"We could also see activity in the San Jacinto Mountains," Martin said. "That could include the recent burn areas."
The Silver Fire broke out Aug. 7, destroyed 48 structures including 26 homes, and scorched more than 30 square miles from Poppet Flats to Twin Pines and Cabazon. The Mountain Fire started July 15, destroyed 23 structures including 7 homes, and it blackened more than 40 square miles near Idyllwild.
The Cleghorn and Inspiration fires broke out Aug. 17 north of Redlands and Loma Linda and scorched more than 100 acres before they were declared contained Sunday.
The Weather Service issued an advisory early Monday for the mountains on both sides of the San Gorgonio Pass for more monsoonal moisture and widely scattered thunderstorms in the mountains and deserts of San Bernardino and Riverside counties.
"The thunderstorms will produce lightning strikes . . . locally strong gusty winds . . . and brief heavy rainfall," the Weather Service advised. "Isolated flash flooding is possible where thunderstorms track repeatedly across the same area . . . Mainly for San Bernardino County desert areas."