The risk of debris flow — a type of landslide that can cause severe damage — around recently burned areas in Los Angeles County is growing as this weekend’s rains approach.
There is now a 10% to 20% chance of significant debris flow for sensitive recently burned areas of L.A. County; that’s up from an earlier estimate of 5% to 10%. The chance of debris flows for other burn scars remains 5% to 10%.
Of the burn scars, the Eaton and Palisades burn scars are of the most concern.
“The most likely outcome is that there might be some shallow debris flows that are kind of minor impacts, but there’s enough of a threat that we definitely at least want to highlight that,” meteorologist Ryan Kittell of the National Weather Service said Friday afternoon.
The period of most concern, which could bring the highest intensity of rainfall over this storm system, is from 4 p.m. Sunday to noon Monday. That is also the time period when thunderstorms could emerge over the region.
There is a 15% to 25% chance of thunderstorms anywhere, and anytime, during this rain event, Kittell said.
A flood watch will be in effect from 4 p.m. Sunday through 4 p.m. Monday for recently burned areas, including the Eaton, Palisades, Franklin, Hughes and Bridge fires. The flood watch will not cover the Mountain fire burn scar in Ventura County.
Forecasters are anticipating isolated areas that could see rainfall rates of half an inch to three-quarters of an inch per hour, Kittell said. Those are rates that have the potential of producing debris flow if they emerge over recently burned areas.
But most areas should see rainfall rates of one-tenth of an inch to one-quarter of an inch of rain per hour. That rate is of an intensity that is beneficial and isn’t intense enough to start producing mud flows or a debris flow.
Accumulated rainfall totals between Saturday and Monday could be higher than initially expected. Los Angeles and Ventura counties now could see between half an inch to an inch, and up to 2 inches in the mountains.
The increased rainfall forecast is a result of the low pressure system, dropping in from Canada, appearing to veer a little bit more to the west — a little bit more off the coast of Southern California — than initially expected, which would make this storm wetter.
Snowfall levels also could be higher than initially projected. Snow levels could fall to as low as 3,500 feet above sea level, and six to 12 inches of snow could fall on the San Gabriel Mountains. There could be 1 to 2 inches of snow on the Grapevine section of the Interstate 5, but there could be less or more, Kittell said.
Expect delays on mountain roads, Kittell said.
This story originally appeared on LA Times
