Life-Threatening Flood Risk for 94% of California Population

On the heels of a significant storm that brought heavy rain, strong winds and mountain snow to the West this week, another system will arrive over the weekend and into early next week, bringing widespread major impacts and travel disruptions. The storm, the latest and most significant in the current 'atmospheric river' setup, will begin to spread moisture ashore in California Saturday night and slowly move inland through Monday. AccuWeather expert meteorologists say that the impacts from the storm will include major flooding, blizzard conditions in the mountains, power outages, landslides, road washouts and life-threatening conditions in some communities. Rounds of large waves from the storm will pummel the California coast into next week. There will be the potential for overwash, coastal erosion, and property damage.  

AccuWeather Senior Director of Forecasting Operations Dan DePodwin stated, “Roughly 94% of California's population, up to 37 million people, is at risk for life-threatening flooding. Due to the numerous mountains and hills, even just a few inches of rain can cause significant flooding. The greatest risk of a widespread flooding disaster is expected across the canyons and hills of southern California, especially in Ventura, Santa Barbara and Los Angeles counties.”

The heaviest rain is expected to focus from near San Francisco to just near and just north of Los Angeles, where several inches may pour down over a couple of days. Locally higher amounts are likely over the west- and southwest-facing slopes of the Coast Ranges. The canyons and hillsides just north of Los Angeles and then westward to Point Conception are at greatest risk for a flooding disaster as 8-12 inches of rain can lead to road washouts and landslides. Burn scar areas are also more susceptible to flooding.

Because of this storm coming only a couple of days after another storm soaked and blanketed the state-- travel and flooding problems from this next storm may be more extensive and much worse than those from the first storm. Expect major urban and small stream flash flooding as well as significant rises on some of the larger rivers in the region with flooding in unprotected areas.  

Strong winds can also accompany the storm and cause power outages. Coastal California and the mountains of southern California through the Sierra are at greatest risk for 50-70mph wind gusts while much of the rest of the state can experience 30-50 mph gusts.

The combination of snow from this upcoming storm and the one that ended Thursday may deliver 5-10 feet of fresh snow on the high country of the Sierra Nevada. The anticipated snowfall should put the Sierra snowpack back on track and then some for the winter. 

Rainfall from this storm and the one earlier this week will push totals since the start of the rainy season in early October to well above the historical average in many cases. Downtown Los Angeles could come close to doubling its pre-storm total of 5.23 inches from Tuesday in less than a week. Rainfall in San Francisco could surpass 15 inches from Oct. 1.