The winter’s biggest storm is expected to hit Southern California later this week, and, once again, it could mean trouble for areas affect by this season’s devastating wildfires.
The storm will work its way south, hitting the San Luis Obispo area on Tuesday night, then move through Santa Barbara and Ventura counties on Wednesday. The highest risk for the Los Angeles area is expected to come Wednesday night through Thursday morning, according to the National Weather Service.
“This is the big one,” says weather service meteorologist Eric Boldt. “This is the largest storm of the winter.”
Along the coast, up to four inches of rain could fall by the end of the 72-hour event, while mountains and foothill areas could get up to six inches. The high rainfall totals could cause rivers and streams to swell, and in areas that have recently burned, that could create problems, Boldt says.
A significant storm system still on track to bring rain to #SoCal Tue-Thu! Flash flooding possible in many areas, flooding& debris flows possible near recent burn areas. #CAstorm#Cawxpic.twitter.com/fNIvBrc489
— NWS Los Angeles (@NWSLosAngeles) March 18, 2018
Recently burned areas, like those recovering from the La Tuna Canyon fire or the Creek fire, are covered in ash and other material that doesn’t absorb water. Heavy rain runs off recently burned soil “as it would run off of pavement,” says the weather service. That can lead to issues with debris flow and mudslides.
How rapidly the rain falls is another factor in the damage it can do. Forecasters say there’s a 20 percent chance that an inch of rain could be falling per hour at the peak of the storm.
”If the 2-4 inches of rain falls gently over the whole 72 hour period, not a lot is going to happen,” Andrew Rorke, a senior forecaster with the weather service, tells KPCC. But if the rain falls in big surges, that could be a problem, “and unfortunately we are forecasting a couple big bursts of rain.”
According to the weather service, Downtown Los Angeles has seen just 3.4 inches of rain since October 1, the start of the wet season. That’s roughly a quarter of the 12.6 normal rainfall total.
Rapidly developing Pacific storm with #PineappleExpress connection looks truly spectacular on satellite imagery today. Main event not expected in #SoCal until later Wednesday and Thursday (slightly delayed), but no decrease in intensity. #CAwxpic.twitter.com/0znlA5FnQU
— Daniel Swain (@Weather_West) March 19, 2018