With more rain on the way, officials warned Sunday of an increased risk of mudslides in burned areas of Los Angeles County, and a 10% to 20% chance of severe flooding and debris flows that could damage roads and homes in and around the devastated areas. wildfires.
“This is a worst-case scenario to prepare for,” said Kristan Lund, a meteorologist with the National Weather Service in Oxnard.
“We are increasingly concerned about burn scars,” said Lund. The scorched trail of the Eaton fire, which blackened more than 14,000 acres, is of particular concern. “These floods and these debris flows can happen in and around or under these burn scars.”
This article is provided free of charge to help keep our community safe and supported during these devastating fires.
A flash flood watch went into effect at 10 a.m. Sunday and will continue until 4 p.m. Monday for areas burned by the Eaton fire in the Altadena and Pasadena areas; the Palisades and Franklin fires in the Pacific Palisades and Malibu areas; the Hughes fire around Lake Castaic; and the Bridge fire in the San Gabriel Mountains west and southwest of Wrightwood. The flood watch started six hours earlier than expected.
“The greatest risk of debris flows will be after 4 p.m. Sunday,” the weather service said.
If you’re not sure you’re close enough to the burn scar, “pretend you are,” Lund says. However, a city like Montebello – which is only 10 miles from the Eaton fire’s scorched area – is not considered close.
(National Weather Service)
“When you’re near a fire, you want to be on the prepared side,” Lund said. Steps people can take to avoid being in or near the area from Sunday afternoon to Monday afternoon; using sandbags to protect property; and, for people who decide to stay, collect supplies in case road access is blocked.
The term “landslide” is an all-encompassing term that can describe any movement of rocks, dirt or debris downhill. “Debris flows” can occur when water flows quickly down and, apart from mud, picks up stones, branches and sometimes large rocks. This is also considered a type of shallow landslide, which can be deadly.
An animated infographic shows the waste flow in action
Landslides are dangerous after a wildfire because the heat of the fire causes the soil to repel water. When the rainfall rate is high — falling more than half an inch per hour — water can begin to flow uphill, instead of percolating underground, and can begin to pick up rocks and debris.
“It definitely has to do with the track of the storm,” Lund said. “They are a major force in the debris flow. They are recent burn scars; they are close to vulnerable communities or infrastructure.”
The terrain is also at risk from this storm. The burn scars are on the south-facing slopes of the mountains, and the storm’s moisture is being drawn south, forecasters said.
Those features can create “very heavy rain in those areas,” Lund said.
The storm’s three-day forecast rainfall totals continue to rise. On Monday, Covina could receive 1.32 inches of rain; city LA, 1.14 inches; Long Beach, 1.12 inches; Canoga Park, 1.05 inches; Santa Clarita, 1.04 inches; Fillmore, 1.02 inches; Redondo Beach, 0.95 inch; and Thousand Oaks, 0.87 inch.
(National Weather Service)
Besides the risk of debris flows, there is the possibility of water spilling over the ocean, as well as damaging winds, and strong thunderstorms, Lund said.
And heavy rain can still happen even if you can’t see lightning or hear thunder. But if you hear or see thunderstorms, “you’re probably going to have higher amounts of rain,” Lund said.
There is a 15% to 25% chance of thunderstorms across the entire Southern California area that includes the recently burned areas, said Carol Smith, a meteorologist with the weather service. Thunderstorms can bring a chance of rainfall of half an inch per hour to three quarters of an inch per hour in isolated areas.
Rainfall rates in excess of half an inch per hour can cause debris flows in burned areas.
Smith said the Palisades fire area could see more than an inch of rain; Eaton’s fireplace can be up to 2 inches.
(National Weather Service)
Light rain started to fall across the area on Saturday night.
The storm will bring the first significant rain of the year. Much of Southern California is still in “extreme drought” and some southern areas and much of the state are still in severe drought, according to the US Drought Monitor.
Officials advised residents in burned areas to use sandbags to direct flow and protect property, clear drainage channels, and obey evacuation orders on debris-covered streets. They also said that residents should keep garbage cans and cars on the street so that storm water can flow freely and avoid contact with dirty runoff.
“If the emergency services say to avoid a certain area, please do that,” Smith said.
Source link
