(Bloomberg) -- A powerful Pacific storm is set to slam into California and the Pacific Northwest, bringing hurricane-like winds and heavy rains that could touch off mudslides in areas burned by this year’s wildfires.
The storm off the coast of Washington will direct “a fire hose” of moisture onshore, starting Saturday and continuing through Monday, said Lara Pagano, a senior branch forecaster at the U.S. Weather Prediction Center. The worst impacts will be in California, where 8 to 10 inches of rain in a few hours could wash mulch and dead trees down hillsides and drop snow by the foot across mountain tops. “We have a big one coming up here and it is going to be impacting much of the West,” Pagano said by telephone. “The impacts are hurricane-like in terms of its winds and wave action, but the actual system itself isn’t a hurricane.” Often called atmospheric rivers, these big Pacific storms can pump as much water as the mouth of the Mississippi River when they crash ashore. A U.S. Army Corps of Engineers study found such events caused 84% of flood damage across 11 western states over a 40-year period. On average, they cause about $1.1 billion in damage.
Flood watches stretch from the Oregon border almost as far as Bakersfield in the south, the weather service said. In addition, high surf warning bringing waves of up to 30 feet are forecast to crash into the coastline from Oregon to south of San Francisco. Winds could reach 45 mph gusting up to 70 mph in some places, and could reach inland into Nevada and Utah. “Periods of heavy rain are expected Sunday morning through Monday morning,” according to the National Weather Service in Sacramento. “This could bring potential ash and debris flows over recent burn scar areas.”
Mud from heavy rain can fill a house in seconds and many areas across California urged residents to evacuate now or be prepared to do so. Santa Barbara County issued an evacuation warning for several canyons in the area, according to a tweet.
The storm has some positives. It could quench wildfires burning across Northern California and help alleviate drought, which currently affects all of California. Fires have killed 3 people, burned almost 2.5 million acres and destroyed 3,629 structures so far this year, according to state statistics.
Like hurricanes, atmospheric river events are ranked on a scale of 1 to 5. Much of coastal Oregon and Northern California will be facing category 4 intensity with some areas reaching 5, according to the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography.
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