Category 5 atmospheric river – stretching 2,700 miles across the Pacific – soaks the northwestern United States

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So far this year, Seattle has seen nearly 6.5 “of rain. With an additional 2-4 inch forecast, the city could receive about 25% of its annual precipitation by Jan. 15 from the Atmospheric River. that soaks the region.

“This soggy start could propel Seattle to its only wettest start to the year on record. The previous wettest period of January 1 to 15 occurred in January 1956, when nearly 7 inches fell in the first half of the month, ”CNN meteorologist Pedram Javaheri said.

Atmospheric rivers are long, narrow regions of the atmosphere – like rivers in the sky – that carry water vapor, according to the National Oceanic and Atmospheric Administration.

This atmospheric fluvial event is rated as Category 5 – the highest level – by the Center for Western Weather and Water Extremes. The potential for flooding is huge, with around 15 million people under some sort of watch or board. Parts of western Washington could see 300% of normal precipitation, according to the Weather Prediction Center.
“Soil saturation levels currently vary from 75 to 95% along the western third of the region. It won’t take a lot of rainfall to cause surface flooding, ”Javaheri explains.
View forecasts across the countryand

There is also a lot of heat in the average atmospheric levels during this particular atmospheric river event. This will increase snow levels to altitudes above 6,000 feet in much of the Cascades with rain falling below that level.

“This will further exacerbate concerns about the flooding as heavy rains fall on heavy snow. The threat of rapid melt, increased runoff and flooding of rivers downstream is something everyone in western Oregon and Washington should be on the alert for, ”says Javaheri.

Higher elevations in Washington could see 2 to 4 inches of rain over the next 24 hours, increasing the risk of flooding and landslides.

The forecast models show the humidity - shown in blue - extending over thousands of kilometers.

Precipitation at low elevations is expected to be between 1 and 2 inches during this time.

In Portland, Oregon, the National Weather Service Office has forecast up to 7 inches of rain for the highest terrain and up to 2 inches for the lowlands until Wednesday morning. Along with this, a strong wind warning is in effect.

Two to four inches of additional precipitation is possible for the Pacific Northwest

Wind warnings extend across the entire Oregon coast, where gusts could reach up to 75 mph. This raises concerns about downed trees, power outages, and possible dangers along Interstate 5.

The impacts of the record-setting wildfires also increase the flood threats for Oregon. According to the Oregon Department of Forestry, more than a million acres have burned. These remaining burn scars make the threat of flooding even greater, due to the charred soil with no vegetation to absorb rainwater. This increases the possibility of flash floods and landslides due to soft ground.

The guilty

The meteorological phenomenon at the origin of all these rains is called an atmospheric river. They are essentially rivers of high humidity in the atmosphere. They carry abundant moisture from tropical regions and release it to other regions in the form of rain or snow.

According to NOAA: “These vapor columns move over time, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi.”

Not all atmospheric rivers are bad. Many times they carry very beneficial rains to areas that need it. Many areas along the west coast will receive 30% to 50% of their annual precipitation in a few events of this type.

However, with a stronger event, it can lead to dangerous flooding and potentially fatal landslides. The atmospheric river that stretches from Hawaii to the west coast was coined the “Pineapple Express” and is one of the most famous atmospheric rivers.
A December 2019 study published by researchers at the Scripps Institution of Oceanography suggests that over the past 40 years, atmospheric rivers have posed a flood risk of $ 1.1 billion for each of those years along the West Coast.

This particular atmospheric river has a range of 2,700 miles with a bull’s-eye on the northwest. That equates to the distance from Seattle to Miami as the crow flies, and the humidity it carries could potentially put January 2021 on the record books.

Hurricane chasers head for the west coast

This atmospheric fluvial event is so large that hurricane chasers will pass through it, dropping buoys.

“In order to truly understand the significance of an atmospheric river event, you have to get close to it. Hurricane hunters fly in and collect valuable data that forecasters then use to determine how a particular atmospheric river will affect the river. Pacific Coast region, ”says CNN meteorologist Allison Chinchar.

It’s their second flight of the season and something they do regularly.

“The Hurricane Hunters first started flying in atmospheric rivers in February 2016 and have sent 6 to 12 flights from January to March since. By itself, it is not that unusual for them to participate in this event, although it’s a popular misconception that once the winds of hurricane season die off, their role also disappears, ”says Javaheri.

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