Heavy rain to enhance flood, mudslide risk in California through Saturday

By Renee Duff, AccuWeather meteorologist
April 07, 2018, 6:54:23 PM EDT

Residents of California are being put on alert for a renewed risk of flooding, mudslides and travel disruptions through the first part of the weekend.

A plume of moisture from the tropical regions of the Pacific Ocean, also known as an atmospheric river, will take aim at Northern and central California through Saturday.

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“This atmospheric river will bring periods of heavy rain to Northern and central California through the first half of the weekend,” said AccuWeather Meteorologist Brett Rathbun.

The heaviest rain will sweep across the region through Saturday.

A total of 1-3 inches of rain may pour down on the communities of Redding, San Francisco, Sacramento and Santa Rosa. This is enough rain to raise the risk of urban and flash flooding.

Heavy rain on Friday afternoon and night led to flooding around San Francisco and Santa Rosa, California, triggering some road closures around the cities. Debris flows were reported in San Mateo County early Saturday morning.

On Friday, Yosemite National Park announced that Yosemite Valley will be closed due to anticipated flooding. The park will evaluate the conditions on Sunday morning and will open as soon as it is safe for visitors. The remainder of the park will remain open, conditions permitting.

Airline passengers with flights through San Francisco International Airport should anticipate delays, while drivers along Interstate 5 can expect times of reduced visibility and slow travel.

Motorists should turn around and find an alternate route if standing water is encountered on the roadways. Some roads may be closed due to high water or debris.

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Even higher rainfall totals, on the order of 3-6 inches or more, are expected for the west-facing slopes of the coastal ranges and northern and central Sierra.

Snowfall will be limited to the highest peaks of the Sierra for the duration of the event. However, enough cold air may be pulled in at the tail end of the storm for precipitation to end as snow over Donner Pass.

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At intermediate elevations, the combination of rainfall and melting snow may trigger rises on small streams and rivers that can lead to flooding.

Around recent burn areas, including the Tubbs Fire, mudslides and debris flows will be a concern.

People who live downhill of burn scars should heed all evacuation notices that are issued. Having an emergency go bag ready is vital in the event of a quick evacuation.

"Despite the threat for flash flooding and mudslides, this rain will help to further fill area reservoirs prior to the dry season this summer," Rathbun said.

Gusty winds may kick up along the coast and over the ridges. The risk of fallen trees and power lines will be heightened due to the saturated ground.

The risk of flooding will lessen heading into Southern California, where the heaviest rainfall will miss to the north. At most, Los Angeles may be dampened by a few showers on Saturday.

"While rain is not uncommon across California during April, a storm of this magnitude is a bit unusual," Rathbun said.

January and February are typically the wettest months of the year in California, with average rainfall rapidly declining from March to April and May.

Fortunately for those hoping to get outside this weekend, Sunday will feature much nicer weather conditions.

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