"The region's first major winter storm could bring rain to Ventura and Santa Barbara counties where the Thomas fire has burned as well as precipitation to residential areas in Los Angeles where other recent blazes have left hillsides bare of vegetation and prone to mudslides and flooding.
"We have a lot of steep, fire-denuded hill slopes where a lot of heavy rain at once could cause flooding and debris flows," said Paul Meznarich, U.S. Forest Service spokesman for the Thomas fire, told CNBC. "We want rain but we don't want a lot of it coming down hard in a short period of time because that brings its own problems with it."
The National Weather Service is forecasting there could be about 2 to 4 inches of rain in the foothills and mountains areas of some of the recent burned areas from the approaching storm. There also is significant rain forecast for the coastal and other areas of the region.
Jayme Laber, a hydrologist at the NWS office in Oxnard, California, said forecast models are showing that rain rates Tuesday into Wednesday in recent burn areas could approach a rate of about one-half-inch an hour, or enough to trigger flashfloods and debris flows.
"Any recent burn area is considered a risk for mud and debris flow in the event there is a large amount of rain," said Capt. Erik Scott of the Los Angeles Fire Department."
https://www.cnbc.com/2018/01/04/aft...ifornia-braces-for-new-threat--mudslides.html