What atmospheric rivers actually mean for the Pacific Northwest


Natasha interviews Dr. Andrew Martin, Research Assistant Professor, Department of Geography, Portland State University

PORTLAND, Ore. (KOIN) — When meteorologists and forecasters say “atmospheric river” in articles or on-air, there is nothing furtive about it, we are forecasting wet weather somewhere for the West Coast. What you may not realize, is how important or detrimental atmospheric rivers may be for Portland and all the surrounding communities around Washington and Oregon.

The KOIN 6 Weather team is keeping an eye on a strong atmospheric river that’s expected to arrive later this week.

Information regarding atmospheric rivers has come from research and information produced by the National Oceanic and Atmospheric Administration (NOAA), which you can visit here.

What exactly is an atmospheric river? It’s the horizontal transport of water vapor that is typically rich from tropical or extratropical moisture. These transient rivers meander and develop from support aloft.

Atmospheric rivers are mostly long and narrow fluid streams; however, they still encompass a relatively large area. Some atmospheric rivers may reach 250 to 375 miles wide, which is enough to impact Washington and Oregon typically in one event. What you may not know is that 30 to 50 percent of the annual precipitation for West Coast states comes from multiple atmospheric river events in a year (NOAA). That means, at times, we are rather dependent on these atmospheric river events to bring us the water that we naturally need.

Now, some of these atmospheric river events may supply extreme amounts of water in a short period of time. According to NOAA’s Earth System Research Laboratory (ESRL), these atmospheric river spikes in the winter may produce 7.5 – 15 times the average flow of liquid water at the mouth of the Mississippi River. Talk about teeming with moisture! These may lead to local flooding, landslides, mudslides, and other natural disasters due to the overload of water.

Lastly, this particular kind of atmospheric river is called the Pineapple Express, which is a non-technical term to refer to an atmospheric river with moisture coming in from the Hawaiian Islands region.

If you’re interested in learning about “Precipitable Water” and “Atmospheric Rivers,” you can watch the video below.

With all of this wet weather in store for the region, many may be wondering what the chances are for the greater Portland and Vancouver areas to see snow in time for Christmas.

Listen to the latest Your Weather Podcast episode on iTunes, Podbean or Spotify, or listen below:

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