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Atmospheric River dumping heavy rain into the Pacific NW October 31, 2012

Posted by mikeheard in Uncategorized.
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A plume of subtropical moisture, aka “AR” atmospheric river, is setting up off the west coast today and targeting the pacific NW. The attached image shows the amount of water vapor in a column of air with the white and blue colors indicating the highest values.

This atmospheric river will likeImagely dump several inches of rain between Portland, OR and up through the Pugent Sound in Washington State. Flood watches and advisories have been issued along the pacific NW coastal areas over the next 48 hours. This rich moisture will weaken considerably as it migrates into the inland NW and into NW Montana.

Astoria, OR picked up 2.49” of rain Tuesday October 30th and month to date precipitation is soaring up to almost 12” for October and for 2012 an impressive 61.55” of rainfall, which is 15.61” above normal.

Portland, OR precipitation for October is up to almost 6”, Seattle is up to 6.14”, Spokane, WA is at 1.50” and Kalispell, MT is up to 2.65”, Missoula 1.82” and Butte with only .36”.

Atmospheric Rivers (AR) are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics. On average, 30%-50% of annual precipitation in the west coast states occurs in just a few AR events, thus contributing to water supply. The strongest ARs can create major flooding when they make landfall and stall over an area.

A well known example of a type of strong AR that can hit the U.S. west coast is the “Pineapple Express”, due to their apparent ability to bring moisture from the tropics near Hawaii to the U.S. west coast. Average ARs are 400-600 km wide.

You can track atImagemospheric rivers on weather satellites using the Total Precipitable Water imagery at this link: http://tropic.ssec.wisc.edu/real-time/mimic-tpw/global/main.html

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