Dangerous holiday storm heads to Southern California: Timeline

LOS ANGELES - A powerful storm system fueled by an atmospheric river is expected to bring dangerous weather conditions to Southern California beginning Tuesday and lasting through the duration of Christmas week.

Forecasters warn of heavy rainfall, strong winds, possible thunderstorms, and changing snow levels that could impact coastal areas, valleys, and mountain communities over several days. Evacuation warnings have also been issued for recent burn scar zones.

Weather Forecast for Tuesday, Dec. 23

The latest forecast and air quality conditions for the greater Los Angeles area, including beaches, valleys and desert regions.

What we know:

Widespread rain in Los Angeles, Orange, Riverside, Ventura, San Bernardino and San Diego counties is expected to begin Tuesday and will intensify going into Christmas Eve and Christmas Day. 

‘Bullseye of this atmospheric river’

"This is all aided by an atmospheric river tapping into all of that moist air mass and all that moist air coming up from the south and southwest. So, we are going to be the bullseye of this atmospheric river here and the impacts are quite great, explained FOX 11 Meteorologist Maria Quiban. 

Southern California prepares for heavy rain, flooding

A powerful winter storm will bear down over Southern California during Christmas week.

Evacuation warnings

Evacuation warnings have been issued for the following burn scar areas:

• Kenneth Fire
• Palisades and Mandeville Canyon
• Eaton Fire
• Sunset Fire
• Topanga Canyon closure (Pacific Coast Highway to Grand View Drive)

How much rain is expected? 

Rainfall totals between Tuesday and late Thursday could reach two to six inches for coastal and valley areas, while mountains and foothills could see six to ten inches, with additional rainfall expected on Friday.

During downpours, flash flooding and mud and debris flow could occur. The storm could also bring gusty winds of 60 mph or more, making for the possibility of weak tornadoes. 

What are the anticipated snow levels? 

Snow levels will initially remain high due to warm air from the south but are expected to drop to between 5,000 and 6,000 feet late Thursday into Friday.

"A lot of our mountain locations or at least some could wake up to a white Christmas on Thursday," said Quiban.

Timeline:

The peak of the winter storm is expected to bear down on Christmas Eve and Christmas Day. See a timeline below. 

• Tuesday, Dec. 23: Widespread light rain begins later in the day and will intensify overnight.
• Christmas Eve: The peak of the storm is expected to drench the region with heavy rain, along with strong winds, with chances of thunderstorms.
• Christmas Day: A second impulse will move across Southern California, bringing another round of gusty winds and heavy rain. Snow is expected at the resort level, the National Weather Service said.
• Friday, Dec. 26: Cooler temperatures and more rainfall are expected. Snow levels will drop to around 5,000 feet.

What's next:

The storm is expected to taper off beginning early Saturday and will dry out for the rest of the weekend into early next week.