Pacific Northwest Braces For Atmospheric Rivers, Flooding Over Next Few Days

Atmospheric rivers could bring up to 10 inches
of rain in the next few days parts of the Pacific
Northwest, raising flooding fears. This map is
forecast rain for the next 7 days. 

The Pacific Northwest has a wet, dark reputation this time of year. The people are nice enough, the weather is not. Sufferers of seasonal affective disorder will do well to avoid places like Seattle and Portland this time of year. 

Usually, it's a grinding, boring day after day realm of drizzle, light rain, fog and chill. Sometimes, though, things can really get out of hand. 

The next few days look what one of those out of hand periods.

A strong atmospheric river is due to hit Washington and Oregon beginning tomorrow and lasting through much of the week. This long lasting deluge is sure to cause at least some flooding and landslides as inches and inches of rain bombard the western halves of Washington and Oregon. 

Some areas of Washington and Oregon could get four to as much as 10 or more inches of rain by Wednesday night.   The Willamette Valley, which runs roughly from Portland to Eugene, Oregon, is expecting three to five inches of rain. 

The Seattle metro area could get two to five inches of rain, which means clogged drains and street flooding, landslides on steep slopes and shallow-rooted trees toppling over as soil turns to loose mud. 

But the real problem looks like it will be in the Cascade Mountains east of Seattle and Portland, and the Olympic Mountains of northwest Washington. 

Five to ten inches of rain could pour down on these mountains, which would quickly race down steep slopes into populated valleys below.  

The atmospheric river - really a series of atmospheric rivers - are tapping into tropical moisture which of course involves warm air. That means snow levels will be high.  You'll probably have to get above 6,000 above sea level to hit snow. That leaves only the higher peaks and volcanoes in the wintry weather. . 

The higher the snow level, the more water will race down the slopes, which is why everybody is so worried about flooding. Flood watches are up for all of the western third of Washington and much of western Oregon. 

Officials in both states said people in flood prone areas should have spent Saturday and as much of the day Sunday as they could getting ready for high water. 

It's always hard to predict exactly how high rivers will get in these situations. But the flood-prone Snoqualmie River is forecast to reach near major flood stage Tuesday, then have a secondary major flood stage peak on Thursday. 

Some of the flooding could extend across the border to Vancouver Island and other areas of southwest British Columbia, Canada, but the worst effects still look like they'll hit south of the border. 

The Cascade Mountains will wring out some of the moisture, so eastern Washington won't get much rain. But the storms will then hit the mountains of Idaho and western Montana, where more rain and snow will fall.

The snow levels in Idaho will be oddly high because of the warm air. Elevations below 8,200 feet or so will probably see mostly rain.  

This type of weather pattern often brings incredibly strong winds to parts of Montana and Wyoming, so those two states will be looking out for that this week.  

Late this week, the super rainy weather in the Pacific Northwest will slow down or stop for about a week, give or take. Then the atmospheric rivers might resume again.