A powerful storm moved toward the Southland Thursday, threatening to cause mudslides and debris flows and prompting officials in one city to issue mandatory evacuation orders before any rain even started falling.

Duarte city officials said the alert level for neighborhoods below the Fish Fire burn area would be raised to red beginning at 7 a.m. Friday, with mandatory evacuation orders taking effect for residents of 180 homes. Classes for Friday were also canceled at Valley View School in anticipation of the storm.

Volunteers were going door-to-door in affected neighborhoods Thursday afternoon, notifying residents about the evacuation orders, and telling them they can voluntarily leave their homes beginning Thursday night. An evacuation center will be set up at the City Hall Community Center, 1600 Huntington Drive.

“Evacuated residents are encouraged to bring medicines and any other items they may need for a minimum 48-hour period,” according to a notice issues by the city. “Meals will be provided to all evacuees and L.A. County Animal Control has made their mobile shelter on site for those that need to bring animals.”

Rain is expected to start falling in the area Thursday night and continuing through Saturday morning, including unusually heavy rainfall on Friday as a result of the region’s most powerful storm so far this season.

Up to an inch of rain per hour is expected in some areas on Friday, with the approaching storm system tapping into a so-called atmospheric river, sucking up volumes of warm moisture, forecasters said. Early estimates are that the region will receive 2-6 inches of rain in coastal and valley areas and between 5 and 10 inches in the San Gabriel mountains and foothills, they said.

The first wave of rain will begin along California’s Central Coast Thursday, then move south and into Los Angeles and Ventura counties Thursday night, with a stronger wave generated by a second storm system slamming into the Southland Friday morning.

“Strong southerly winds combined with ample moisture will lead to periods of very heavy rain, with rain rates at times of around 1 inch per hour,” according to the National Weather Service. The rain is expected to taper off Saturday morning, causing the threat of flash flooding to disappear around noon, although scattered showers are possible through Saturday evening.

“There will be the threat of flash flooding with mud and debris flows in and around the recent burn areas, especially with Friday’s storm,” according to the NWS.

A flash flood watch will be in effect from Friday morning through Saturday morning, with the greatest threat of flash flooding developing in areas below slopes denuded in wildfires, according to the NWS. Widespread urban roadway flooding is also possible, along with flooding in creeks and small streams, and rock and mudslides, especially near canyon roadways, warned an NWS statement.

In Duarte, residents were warned to keep vehicles, trash bins and other obstructions off roadways, and a series of streets were closed in advance of the storm. Closures were ordered at Royal Oaks and Greenbank; Bettyhill and Conata; Royal Oaks and Mel Canyon; eastbound Fish Canyon at Mel Canyon; westbound Fish Canyon at Mel Canyon, Mountaincrest and Deerlane; Brookridge and Tannencrest; and Sunnydale Drive and Westvale Road.

Glendora city officials issued a yellow alert, also ordering residents to remove vehicles and other obstructions from streets to ensure they are not washed away in a mudflow or obstruct emergency vehicles trying to reach the area.

High surf is expected along the coast through Sunday as a result of a large storm-generated westerly swell, with the biggest surf expected Saturday. A high surf advisory will be in effect from 7 Thursday evening until 7 a.m. Sunday, said the NWS, warning of surf of 6 to 9 feet Thursday, increasing to 8 to 13 feet on Saturday before diminishing that night.

“Large waves and strong rip currents will increase the risk of ocean drowning for swimmers and surfers,” according to the NWS statement. “Large breaking waves can cause injury, wash people off beaches or rocks and capsize small boats near shore.”

Also in effect and affecting sailors is a small craft advisory that will be in effect from 9 Thursday evening to noon Friday and a gale watch — issued in cases of winds of between 34 and 47 knots — from Friday afternoon through late Saturday night. During that period, there could be combined seas of 14 to 17 feet and inexperienced mariners should stay off the water, the NWS said.

In the mountains, heavy snow is expected at higher elevations, along with damaging 70-mile-per-hour gusts, the NWS said. The snow level will vary from as low as 6,000 early Friday to 8,000 feet Friday night, then fall back to 6,000 feet. A winter storm warning will be in force in the San Gabriel mountains from Friday morning through Saturday morning.

Between 1 and 2 feet of snow are possible above 8,000 feet and between 6 and 12 inches above 6,000 feet.

“Heavy snow, gusty winds, low visibility in blowing snow, and icy roads make for dangerous driving conditions,” according to the NWS. “Only travel in an emergency,” an NWS statement said, adding motorists traveling in mountain areas should have a flashlight, food and water, and extra clothing and blankets.

The region has been rained on a great deal more than usual. Normally, downtown L.A. would have received 8.96 inches of rain by this time of the year in the season that runs from October to April, but it already has had 16.25 inches, according to NWS forecasters.

The NWS forecast a combination of foggy and partly skies in Los Angeles County Thursday and highs of 61 degrees Fahrenheit on Mount Wilson; 63 in Avalon and at LAX; 65 in Long Beach; 66 in Lancaster; 67 in San Gabriel and Saugus; 68 in downtown L.A., Pasadena, Burbank and Palmdale; and 70 in Woodland Hills.

Partly cloudy skies were forecast in range County, along with highs of 62 in Newport Beach and Laguna Beach; 63 in San Clemente; 68 in Anaheim; 69 in Fullerton; 70 in Irvine; and 71 in Yorba Linda.

Friday’s temperatures will be between 2 and 12 degrees lower, then will fall slightly on Saturday amid showers. More rain is expected Tuesday.

—City News Service

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