By Reginald Stanley. Posted December 22, 2019, 8:12 PM.

Following a period of high pressure and offshore flow, a significant pattern change is taking place across California this weekend as a large trough brings in a Pacific storm front over the region late Sunday.

The trough is expected to usher in several significant Pacific storms throughout the week, with the first arriving tonight and continuing through Monday. Light, intermittent showers are forecast to occur between storms as well, before a second, colder storm arrives late Christmas Day through Thursday. Precipitation amounts through Tuesday are predicted to fall between 0.5 and 1 inch across much of the Inland Empire and San Diego County, with locally higher amounts up to 1.5 inch possible in favorable locations. Higher precipitation amounts between 1 and 2 inches are predicted across lower Los Angeles and Orange counties, as well as Ventura County. The eastern valleys, including Hemet, San Jacinto and Anza, are predicted to be somewhat drier with precipitation amounts between 0.25 and 0.5 inch through Tuesday. Less than 0.25 inches is predicted across the deserts. Snow levels are forecast to fall to between 5000 and 6000 feet above sea level Monday, with heavier snow above 7000 feet.

A second, colder Pacific storm front will arrive late Wednesday night, and will continue into Thursday. Widespread precipitation is expected, however intensity remains uncertain due to computer forecast model differences. Details including snow levels and precipitation amounts will be updated throughout the week as the storm dynamics become more certain.