An extreme atmospheric river causes significant flooding across the Pacific Northwest

Heavy, record-breaking rainfall is causing significant flooding, avalanche, and landslide risk across America's Pacific Northwest.

An extreme atmospheric river event, also known as the Pineapple Express, has drenched portions of western Washington and Oregon. While rain started over the weekend, Monday saw the heaviest rainfall with several large metro areas like Seattle and Portland, breaking daily records.

The deluge has prompted the National Weather Service to issue Flood Warnings and Watches due to excessive runoff affecting rivers, creeks, streams, and other low-lying and flood-prone locations. Several warnings will likely remain active until Wednesday as river levels slowly return to normal. Video shows flooded roads in Des Moines, Washington on Monday:

Seattle saw 2.97 inches of rain on Monday. According to the National Weather Service, this was the first 2+ inch total in February in 26 years. It was also Seattle's 10th-wettest day of all time and the 3rd-wettest February day.

Additionally, Seattle usually only sees one day per year with daily rainfall totals of 2 inches or greater. This year it has already occurred twice, on January 6 and February 28.

Other daily records set in Washington on Monday include:

Several Oregon locations also experienced astonishing rainfall totals. The most notable was at Astoria, where 2.98 inches was recorded for the calendar day. More than double the old record of 1.40 inches set on February 28, 2013.

Warm southerly flow also caused snow levels to rise considerably along the Cascades. Heavy rain over a deep snowpack is a particularly dangerous situation as it can weigh down on the existing snow and cause large avalanches. On Monday, the Washington Department of Transportation was clearing snow off of US 2 near Stevens Pass after an avalanche occurred in the area.

While rain will remain in the affected areas through Wednesday, it will be more spotty and less persistent. Conditions should continue to slowly dry out allowing river levels to recede and snow levels to gradually lower, decreasing the risk for river flooding and avalanches. The rest of the week will be mostly dry with the return of unsettled weather by next week.