A voluntary evacuation order was issued Monday for residents living in the Cranston Fire burn area due to thunderstorm conditions stemming from Hurricane Rosa, with flood and mudslide risks exacerbated by hillsides stripped of vegetation by the arson-caused blaze.
The National Weather Service issued a flash flood watch for parts of Riverside County that began at noon and will continue through Monday evening.
“Flash flooding can happen anywhere, but of particular concern will be fresh burn scars where heavy rain can cause a cascade of rocks, debris and mud down canyons and steep slopes,” according to the NWS.
The Riverside County Emergency Management Department on Saturday warned residents near Idyllwild and Lake Elsinore that rain in the Cranston and Holy fire areas could trigger mud and debris flows in locations where the vegetation was consumed by the fires.
“Powerful mixtures of mud, rocks, boulders and trees” could flow into streets, backyards and homes, depending on the speed and mass of the runoff, the department warned.
Much of the hurricane’s moisture dissipated Sunday as it moved into colder waters off the Baja California peninsula, NWS forecaster Ivory Small said.
Rosa was a Category 4 storm on Thursday, but had been downgraded to Category 1 by Sunday.
But enough moisture remained to prompt the NWS to issue a flash flood watch for the deserts and mountains of southeastern California and western Arizona.
Meteorologists say the storm will dump about an inch-and-a-half of rain in mountain areas, a half-inch in the Coachella Valley and a half-inch to three-quarters of an inch in some high deserts areas, such as the Morongo Basin, through Tuesday.
Riverside is expected to receive nearly a quarter-inch of rain through Tuesday, according to the NWS.
Periods of localized heavy rain could cause flooding in poor drainage areas and normally dry washes and arroyos in the flash flood warning area, which includes eastern Riversive County and all of Imperial County, the NWS said.
“After (Monday’s) activity in the afternoon, it should be weakening,” Small said. “On Tuesday, the sun starts to become more dominant and the clouds from the dissipating hurricane push east to Arizona.”
Flash flooding in the Coachella Valley caused a portion of a bridge to wash out in the Salton Sea community of North Shore Monday, trapping a driver whose pickup truck landed in the canal below.
The eastern portion of the bridge near Avenue 70 and Cleveland Street washed out, leading officials to close the roadway. The truck driver had to be cut out of the vehicle by county firefighters, but declined to be taken to a hospital.
Officials from Riverside County Transportation Highway Operations said it was uncertain how long it would take for the bridge to be repaired.
The rain from Rosa isn’t all that’s in store for the region. A separate, more winter-like system could bring more rain into the area on Wednesday, Small said.
On Monday afternoon, the County Emergency Management Department issued a voluntary evacuation order for burn area residents in Hurkey Creek, Lake Hemet, Apple Canyon and Fleming Ranch.
Two care and reception centers were opened for evacuated residents, at Idyllwild School, 26700 state Route 243, and Pathfinder Ranch in Mountain Center, 35510 Pathfinder Road.
Further alerts will be posted to www.RivCoReady.org/AlertRivCo .
Evacuation warnings — which are advisory but recommend that people take precautions and be prepared to go — generally will be issued 24-48 hours before a storm, officials said. Evacuation orders will be issued 6-12 hours before impacts.
Riverside County and some municipal fire departments will have sandbags available in limited quantities.
More information is available at www.RVCFire.org, or by contacting individual fire stations, officials said.