Hurricane remnants plus winter storm could slam Riverside mountains over 6 days

INDIO, Calif. – The remnants of Hurricane Rosa plus a winter storm were expected to drop half an inch of rain in the Coachella Valley beginning tonight and 1.5 inches of rain over six days in the mountains west of there, a National Weather Service forecaster said.

The Riverside County Emergency Management Department on Saturday warned residents near Idyllwild and Lake Elsinore that six days of rain in the Cranston and Holy fire areas could trigger mud and debris flows around 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 was dissipating 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.

There will still be enough moisture left to prompt the NWS to issue a flash flood warning for the deserts and mountains of southeastern California and western Arizona.

Small amounts of rain were expected to fall Sunday night, with the real activity expected Monday afternoon.

Meteorologists say the storm will dump 1 to 1.5 inches of rain in mountain areas, 0.25 to 0.75 inch in the Coachella Valley and .25 to .5 inch in some high desert areas, such as the Morongo Basin, through Tuesday.

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 Riverside County and all of Imperial County, forecasters said.