Flash flood warnings issued in LA County. See the storm timeline

Flash flood warnings and widespread flood watches are in effect Saturday as the second wave of a mid-November storm unleashes steady rain in Southern California, raising the threat of flooding and debris flows in the region’s recent wildfire burn areas.

Parts of Los Angeles County, including the Malibu area, Torrance, Inglewood and Compton, were under flash flood warnings expected to continue into midday. A flash flood warning also was issued for most of Ventura County, including Oxnard and Simi Valley.

Evacuation orders were in effect for some properties considered at high-risk for debris flows in the Palisades, Eaton and other fire zones. Evacuation warnings were in place for other burn areas, meaning residents should be prepared to leave.

The system, which could also produce thunderstorms, hail and even small tornadoes, moved into Santa Barbara and Ventura counties Thursday night and brought scattered showers to Los Angeles County Friday. Rainfall was expected to intensify Saturday morning with flood watches in effect and through Saturday night for parts of Los Angeles, Orange, San Bernardino and Riverside counties.

Rainfall rates of up to 1 inch per hour are possible, increasing the flood risk.

About 23 million people are under some type of flood alert Saturday.

Here’s what to know about the mid-November storm.

Storm timeline

• Overnight and early Saturday morning: Steady rain with increased threats for flooding and debris flows. Flood watches go into effect for a widespread area until 10 p.m. A flash flood warning was in effect for the Malibu area and other parts of LA County until noon. Expect moderate to heavy rain between 5 a.m. and midday.
• Midday Saturday: Rainfall rates reach their peaks with an increased chance for thunderstorms.
• Saturday evening: Rainfall starts to wind down, but showers continue into the night.
• Sunday: Lingering showers, but most areas will start to dry out.

A separate, but less powerful, system appears on track to deliver more rain early next week.

Temperatures will be in the 60s for most of the region. Strong wind gusts are possible.

Rain and snowfall estimates

• Most areas: 2 to 5 inches. Normal precipitation for November in downtown Los Angeles is 0.76 inches.
• Mountains and foothills: 3 to 6 inches
• Snow levels: Around 8,000 feet, lowering to 6,000 feet Thursday night into Friday. A few inches are possible at resort level.

If Los Angeles receives more than 2.43 inches of rain Saturday, this will be the wettest November on record. The current mark was set in 1985. 

Rainfall estimates and the storm timeline might change, depending on the path of the storm.

Evacuations

On Friday morning, the city of Los Angeles said evacuation orders were issued for “select vulnerable properties within burn scar areas” beginning at 8 p.m. Friday through 8 a.m. Sunday. LAPD Chief Jim McDonnell said the evacuation warnings that had been issued in the Pacific Palisades, especially areas near the burn scar zones, are now under evacuation orders “due to the increased risk of mud and debris flow.”

“Recent burn areas, including those impacted by the January 7 wildfires, remain highly susceptible to mud and debris flows,” the city said in a statement. “Residents in these areas are urged to stay vigilant, monitor official weather updates, and avoid unnecessary travel during the storm—especially if they have been advised of potential mudflow risks in their neighborhoods.”

Los Angeles’ Emergency Operations Center will activate at 6 p.m. Thursday.

Evacuation warnings also were issued Friday for parts of Ventura County.

“If your home is within the impacted area, please evacuate before 8 p.m. tonight,” McDonnell said. “Take your family, pets, medications, important documents, and any essentials you may need.”

Similarly, Los Angeles County updated the evacuation warnings to orders in Altadena, urging those who live in recent burn areas to leave their neighborhoods by 8 p.m. Friday. The evacuation order was expected to expire at 8 a.m. Sunday.

In San Bernardino County, an evacuation warning is in effect for Mount Baldy Village, northeast Yucaipa, East Highland, Wrightwood, Seven Oaks and Forest Falls.

Debris flow risk

After months of mostly dry weather in Southern California, dry soil can quickly become over-saturated and unable to adequately absorb moisture. The result can be damaging mudslides and debris flows, which collect large rocks, trees, branches and other items as they move downhill, sometimes with alarming speed.

In wildfire burn areas, the risk is higher. Burned soil repels water, meaning debris flows can be triggered with much less rainfall that areas with healthy vegetation.

Road closures

In the Palisades Fire area, Caltrans will close Topanga Canyon Boulevard between Pacific Coast Highway and Grand View Drive at 10 p.m. Thursday. Caltrans officials said motorists should expect the stretch to remain closed at least through the Friday morning commute, but potentially through the weekend, depending how the storm develops.

That stretch of Topanga Canyon has been undergoing nightly repairs, with the road closed between midnight and 5 a.m.

California drought update

Moderate to severe drought was reported in pockets of Southern California with most of the state drought-free, according to Thursday’s Drought Monitor update.

Nine percent of California was in severe drought, the second-least severe of the Monitor’s four drought categories. Areas include most of Orange County, western Riverside County and slivers of San Bernardino County.

About 32 percent of the state was in moderate drought. Nearly 50 percent of California was drought-free.

At this time last year 5 percent of the state was in severe drought with 17 percent in m moderate drought. Three months ago near the end of a hot and dry summer, 23 percent of the state was in severe drought with nearly 40 percent in severe drought.

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Source: NBC Los Angeles