CNN
—
More than 10 million people were under flood warnings across the Pacific Northwest on Tuesday as a powerful storm surge Attacks the region Already wetted by previous atmospheric rivers with heavy rainfall.
More than 8 inches of rain has already fallen in the region in the past 24 hours and rivers are beginning to rise to flood stage, with many rivers forecast to reach major flood levels in the next 24 hours.
In Washington, The Skagit And Snoqualmie Rivers are of particular concern, with roads, farms and even some residential areas predicted to flood. Water levels of areas Skokomish Rivers in western Washington rose to moderate flood stage Tuesday morning Grace River Heavy flooding in southern Washington.
More heavy rain on Tuesday will only worsen parts of Oregon’s Cascade Mountains, southern Washington and northwestern California. According to the Weather Forecast Center, there is a slight risk of heavy rain, or a Category 2 of 4, on Tuesday.
A flood watch extends from coastal Oregon and Washington to northeastern Washington and northern Idaho. While most expire on Wednesday, some last until Thursday.
Washington’s Olympic Mountains could get more than a foot of rain, and stacks could see 5 to 9 inches, the weather service said. Along the coast, residents can expect 3 to 5 inches and 1 to 3 inches in inland lowlands.
cnnweather
As of Tuesday morning, there will be additional rain.
Monday and Tuesday Atmospheric River already records impressive total: Olympic National Park in Washington record 8.67 inches in the last 24 hours More rain will come.
The weather service advises flooded residents to stay indoors or seek higher ground if shelter is not available.
Thursday and Friday, storm activity is forecast to decrease across much of the Northwest, but showers and some high-altitude snow are possible.
But the interval of wet weather may be short-lived. Forecast computer models show some early signs of another atmospheric river hitting the region by the end of the week.
Once this week’s atmospheric river comes to an end on Wednesday, the exact strength and overall impact of this potential event will become clear.
A sequence of atmospheric rivers is called a AR family, started on Saturday and didn’t leave much of a gap before the Monday night set-up. This lack of recovery time is a major factor in increasing flood risk.
Parts of Utah and Colorado received snow on Monday, bringing snowfall totals to several feet in some places throughout atmospheric river events. 50 inches in Collins, Utah, 49 inches in Rabbit Ears Pass, Colorado.
A stage 4 of 5 storm surge is forecast to hit the entire coast of Oregon this week. The storm surge peaked at 5 out of 5 in the northwestern part of the state Monday night into early Tuesday morning.
But this latest round of moisture has also brought warmer temperatures, including a high of 65 degrees in Portland, which tied the city’s all-time high for December last year, 1993.
These warm conditions have promoted snowmelt across the Pacific Northwest and lead to excess runoff and rising creeks and streams.
Heavy rainfall also increases the risk of landslides or debris flows in wildfire-burned areas because the subsoil has less capacity to absorb moisture.
Not all atmospheric river phenomena are bad. In fact, AR event stages 1 and 2 are often considered beneficial rains and are much needed across the western United States to produce water supply levels. But AR event levels 4 and 5 are more dangerous than beneficial because the flooding and travel hazards outweigh the benefits.
CNN’s Alison Sinzar and Sarah Tonks contributed to this report.
