“A dangerous scenario is unfolding,” the National Weather Service (NWS) warned early Wednesday.

The NWS’ Weather Prediction Center issued a rare Level 4 out of 4 “High Risk” of flash flooding for places just north of Los Angeles in Santa Clarita, Burbank and Glendale through Christmas morning.

Los Angeles itself is under a Level 3 flood threat, as the region, home to more than 12 million people, prepares for a widespread 3 to 5 inches of rain within a 24-hour period.

Flash flood warnings were issued early Wednesday across Santa Barbara and Ventura counties.

LA officials emphasized the severity of the flood threat on Tuesday, asking people to stay aware as they celebrate Christmas Eve and prepare for potential flash flood emergencies.

This comes after days of rain have saturated soils, creating prime conditions for dangerous flooding. Mudslides and debris slides are expected, according to the NWS.

The Los Angeles Fire Department has issued evacuation warnings for debris flows for several areas around burn scars from January’s wildfire disaster through 11 p.m. Thursday.

Ash from wildfires creates burn scars—a water-repellent coating that prevents the ground from absorbing water and causes the area to be predisposed to flash flooding and debris flows.

People near the Palisades and Eaton Fire burn scars were urged to take protective action earlier in the week.

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The Los Angeles County Department of Public Works distributed sandbags in Altadena and other vulnerable communities.

Visit the City of Los Angeles website for the latest on evacuation orders.

The FOX Forecast Center warns that as the system moves onshore, atmospheric instability will be high enough to trigger severe thunderstorms, some of which could even produce a tornado.

In addition to the heavy rain, this storm system could pack wind gusts up to 80 mph along the coast.

Wind Alerts have been issued for most of the California coast through Thursday.

This comes after an atmospheric river soaked the region over the weekend and produced deadly flash floods in the northern part of the state.

The rain snarled holiday travel and could cause yet more delays Wednesday at San Francisco International and Los Angeles International Airport.