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Atmospheric river returns to the West Coast

By Jennifer Gray, CNN meteorologist

Another deluge is on tap for the West this week as a series of systems line up and take aim at the Pacific Northwest coast.

These storms have the potential to cause major flooding and landslides in areas that are already saturated with rain. The first system is winding down. It brought heavy rain, snow and gusty winds to parts of the Washington, Oregon and Northern California coasts.

Parts of Northern California saw wind gusts as high as 50 to 60 mph Tuesday morning. Crescent City reported the highest gust at 65 mph.

“By late Thursday an atmospheric river event is expected to begin,” said the National Weather Service in Seattle.

This next event will bring an abundance of moisture, mostly to Washington and Oregon.

An atmospheric river is a plume of moisture that streams in off the Pacific Ocean. Similar to a fire hose, it shoots moisture into one area for an extended period of time, resulting in heavy rain.

This particular event will be a level four out of five on the atmospheric river scale.

Mudslides and flooding concerns

The NWS office in Seattle is concerned about landslides.

“Due to the wet start to the month and this additional rainfall the soils are fairly saturated. Additionally, high winds are causing trees to fall and adding to the general instability of soils,” the weather service said.

The other concern will be flooding. Some areas in the mountains that currently have snow below 9,000 feet will be getting all rain with this system.

Heavy rain on top of snow, results in the snow melting quickly and rushing down the mountains, creating more flooding hazards. “Heavy rains and melting snow will cause rivers … to rise dramatically though Friday,” the weather service said.

There’s still some forecast uncertainty

There are still quite a few questions as to where exactly the heaviest rain will fall.

With these kind of systems, sometimes it’s not about how much rain you see, but how quickly it falls.

“Rain amounts over a 48- to 54-hour period could exceed 4 to 7 inches in the hardest-hit areas of the north Coast Range and the south Washington/north Oregon Cascades and foothills,” the weather service in Portland, Oregon, said.

More widespread rainfall amounts look to stay under 2 inches, but even forecasting that is a challenge at this point. Coastal areas of Washington and Oregon could see 3 to 6 inches of rain from this system.

Why this rain won’t help the drought

While rain is needed in the West, most of the rain that will fall with this event won’t be falling where the West needs it most.

There is no drought in western Washington, where the flood threat is, and the areas that are in drought aren’t getting as much rain.

Northern California needs an exceptional year to try to get back to somewhat normal water levels.

It’s going to take a more consistent rainfall over the entire winter season to improve the drought.

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