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Weekly Weather Event -Week of September 13th

September 18, 2021

The Pacific Northwest is set to see some much needed rain this weekend. A strong cold front and strong atmospheric moisture is set to bring heavy rain throughout western Washington and Oregon, and the heaviest totals are expected along the Olympic Peninsula, coastal ranges, and the Cascades. This system will also mark the first strong atmospheric river event of the cool season.

Atmospheric are long, narrow regions within the atmosphere that transport high amounts of water vapor. One of the most well known atmospheric rivers is the Pineapple Express, an atmospheric river that brings moisture from the tropics near Hawaii to the West Coast of the United States.

When these rivers make landfall, they tend to bring strong rain or snow. Stronger systems can result in flooding and mudslides, especially if they stall over land. However, atmospheric rivers also can bring much needed precipitation and help build snowpacks in the winter time. They are especially crucial in the Western U.S. where atmospheric rivers can contribute to nearly half of annual precipitation.