By Reginald Stanley. Posted December 21, 2021, 7:06 PM.

An atmospheric river event is forecast to bring an active period of wet, stormy weather to Southern California later this week, leading from Thursday up through Saturday (Christmas Day).

The heaviest rain and mountain snow late Thursday night through Friday morning, with that storm departing the region Friday evening. Localized flash flooding is possible during this time period from the coasts to the mountains and even deserts, according to the National Weather Service. In the coasts and valleys, precipitation totals between one and two inches are predicted through Friday morning, with potentially higher amounts in favorable foothill and mountain locations. Snow levels are expected to remain fairly high during the brunt of the storm, hovering around 8000 feet above sea level, however snow levels may drop to 7000 feet or lower throughout Friday as colder air moves in, while precipitation moves out.

A second, weaker storm will follow late Friday night and into Christmas Day, with lower snow levels in the 5000 to 6000 foot range. Precipitation amounts from that system is forecast at approximately 1/2 inch in the valleys and coasts, and up to 1.25 inches in the mountains and favorable foothill communities by the end of Saturday. Residual moisture is expected to clear out from the region overnight into Sunday morning. A chilly weather pattern under a longwave trough could bring additional wet weather chances around the New Year.