All Weather News

Flash Flood Threat for California

14 Nov 2017, 4:26 pm

The latest Pacific storm is set to bring heavy rain and snow to the West Coast of the United States.  The heaviest rainfall will occur in Washington and Oregon; however, northern areas of California may pick up as much as 6 inches.  Travel will be impacted from Seattle south to San Francisco Wednesday into Thursday.

A big concern with the incoming rain will be the threat of flash flooding in California.  Burn scar areas in Santa Rosa and other nearby communities ravaged by the state’s deadliest wildfire disaster in October will be most susceptible to flooding.

Locations that are downhill and downstream from burned areas are most at risk for mudslides and debris flows, especially near steep terrain.  Rainfall that would normally be absorbed into the ground will run off very quickly in burn scar areas.  Burned soils repel water much like asphalt or concrete.  As a result, much less rain is required to produce a flash flood.  In this case, a forecast of just 1 to 3 inches in the Santa Rosa, Napa, and Sonoma areas is cause for concern.

Beyond the middle of the week, another Pacific storm will impact northern California by Sunday.  This is the start of the rainy season for the West Coast, after all.

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Meteorologist Joe Astolfi

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