As the new year begins, another series of atmospherically fueled storms is poised to flood California. The threat of flooding will return to the state just days after devastating storms over Christmas week caused rivers to swell and soil to inundate.
The midweek storm lacks the extreme elements of last week’s flooding, but it arrives with the limits already reached. With little room for additional water, rainfall amounts, not total precipitation, will determine whether there will be a problem as California enters the new year under another active weather pattern.
The first low pressure system is expected to reach Southern California late on New Year’s Eve, then spread north through much of the state into the new year. The National Weather Prediction Center threatened Level 2/4 flooding for much of Southern California on Wednesday and Thursday.
Coastal and valley areas such as downtown Los Angeles could see 1 to 2 inches of rain, while hilly and mountainous areas could see 2 to 4 inches. Even moderate torrential rainfall can cause flooding, landslides, and debris flows, especially near burn scars and steep terrain.
Evacuation warnings have been issued for some areas of Los Angeles County near recent burn scars as rain began falling Wednesday night. The voluntary warning begins at 11 a.m. Pacific Time and is intended to give residents time to prepare for possible debris flows and landslides.
The Wrightwood area of San Bernardino County, which was damaged by Christmas Eve flooding and the remains of the Bridge Fire, is under another evacuation order as debris flows and the threat of debris flows return.
California Governor Gavin Newsom announced that the state had pre-positioned workers and equipment to Los Angeles and Ventura counties before the rains arrived.
The timing makes it especially interesting in Southern California, where the 137th Tournament of Roses Parade will be held Thursday morning in Pasadena. Rain falling Wednesday night could affect parade participants camping along the route, with the downpour continuing into Thursday morning. According to the National Weather Service, the rainy Rose Parade is expected to be the first since 2006.
This system is just the first of three systems in the conga line that could affect flooding conditions through early next week. Conditions will change late Friday into Saturday as colder air reduces snowpack below major mountain passes, including Interstate 80 through Donner Pass. More than a foot of snow could fall at Sierra Nevada ski resorts, but the exact snowfall amount remains unknown and could make mountain travel dangerous.
