Heavy Rainfall Poses Flood, Debris Flow Risks in Riverside County

Heavy Rainfall Poses Flood, Debris Flow Risks in Riverside County

News Staff

A storm bringing with it heavy rainfall and strong winds moved into the Inland Empire Thursday, prompting mandatory evacuation orders in parts of the Temescal Valley and Lake Elsinore due to fears of mudslides, debris flows and flash-flooding along burn-scarred areas in the Cleveland National Forest.

Around 10 a.m., the National Weather Service issued a flash flood warning for Riverside County and parts of Orange County that will remain in effect until at least noon due to the threat of flooding in the Holy Fire burn area.

Forecasters said radar showed “very heavy rainfall entering the Holy burn scar,” according to the NWS. “Flash flooding will likely begin shortly and debris flows will likely begin in Trabuco Canyon and possibly in the Indian, Temescal, Coldwater, Horsethief, Rice, McVicker and Leach Canyons which drain towards Lake Elsinore. Debris flows can more quickly and with little warning.

“Some locations that will experience likely flooding include western Lake Elsinore, Temescal Valley and Ortega Highway 74,” according to the NWS.

In a 24-hour period ending at around 10 a.m., the storm had dropped 0.63 of an inch of rain in Corona, 0.30 of an inch in Riverside, 0.63 of an inch in the San Gorgonio Pass near Banning and 1.93 inches near Silverado, according to the NWS. Palm Springs and Cathedral City in the Coachella Valley had no recorded rainfall.

The county’s Emergency Management Department declared the need for immediate evacuations around 3 p.m. Wednesday, replacing a prior warning in which residents were advised to voluntarily relocate ahead of the heavy rain, which is expected to peak late Thursday morning.

The mandatory evacuation applies to Lake Elsinore residents along Alberhill Ranch Road and Amorose Street, residents west of Laguna Avenue, as well as residents on Glen Eden Road south of Corona, the Glen Ivy Hot Springs community, the Horsethief Canyon community and the area around McVicker Park in Lake Elsinore.

A map delineating exactly which neighborhoods are impacted is available at http://rivcoready.org/Have-a-Plan/Flooding/Storm-Ready .

A care and reception center is open at Temescal Canyon High School, 28755 El Toro Road in Lake Elsinore.

Residents can house large and small animal at the care and reception center at the San Jacinto Valley Animal Campus, 581 South Grand Ave. in San Jacinto.

The National Weather Service is forecasting up to one inch of rain in Lake Elsinore, Corona and Riverside with the heaviest rainfall expected late Thursday morning.

The county mountains are expected to receive up to 3.75 inches of rainfall Thursday, according to the NWS. Snow levels are predicted to drop to 6,000 feet.

The NWS issued a winter weather advisory for portions of the Riverside County mountains above 6,000 feet from noon Thursday to 2 a.m. Friday.

The Coachella Valley will receive around two-tenths of an inch of rain and the San Gorgonio Pass near Banning is expected to see up to 2 inches of rain, according to the NWS.

A flash flood advisory will be in effect from 6 a.m. Thursday to 3 a.m. Friday for the Riverside County mountains, the San Bernardino County mountains and Orange County inland areas, which includes a small southwest portion of Riverside County west of La Cresta.

The burn-scarred slopes — the result of the August Holy Fire that began on the Orange County side of the Cleveland National Forest — are highly susceptible to heavy runoff that could prove damaging, according to county officials.

Multiple community meetings have been held over the last two months to inform residents of the risks and what to do in the event of a big storm. The Holy Fire, allegedly the work of an arsonist, scorched roughly 23,000 acres.

Rainfall is expected in the burn zone created by the 13,000-acre Cranston Fire, but officials do not anticipate the rain will be heavy enough to trigger debris flows. But both Idyllwild and Pine Cove were included in a flash flood watch in effect until 3 a.m. Friday, but as of 3 p.m. Wednesday no evacuation orders had been issued for the area.

The storm was generating strong, gusty winds, prompting the NWS to issue a wind advisory from 8 a.m. to 6 p.m. for the San Gorgonio Pass near Banning, the county valleys, Idyllwild and Pine Cove. The Coachella Valley was not included in the wind advisory.

Rainfall rates of around one-half inch per hour will be possible on the southwest facing slopes of the San Gabriel and San Bernardino mountains late Thursday morning, said NWS meteorologist Greg Martin. The heaviest rainfall is expected to clear the mountains by Thursday afternoon followed by widespread rainfall Thursday evening.

High temperatures Thursday are expected to reach 63 degrees in Riverside, 56 in the county mountains, 68 in the San Gorgonio Pass near Banning and 75 in the Coachella Valley.

A second, weaker storm is expected to bring rain Saturday afternoon into Sunday morning.