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Daryl Ritchison, WDAY, Published December 01 2012

Weather Talk: ‘Pineapple Express’ brings heavy rain to California

Rivers flood. We know that all too well here in the Red River Valley. But another kind of river has been causing flooding in California that might be less familiar – an atmospheric river.

Atmospheric rivers are narrow regions in the atmosphere, often 100 to 300 miles in width, that contain high concentrations of water vapor. Like real rivers, they come in all shapes and sizes and often contain meanders. Using specialized satellite data (water vapor imagery), these rivers of concentrated water vapor are often easily detected.

One type of atmospheric river is the so-called “Pineapple Express,” when tropical moisture near Hawaii is transported into the West Coast. These narrow flows of moisture can also come from nontropical sources, and that has been the case with the heavy rain that has been impacting northern California in recent days.

Although these atmospheric rivers can cause flooding, more often they just bring beneficial moisture to the western region.

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or write to WDAY Stormtracker, WDAY-TV, Box 2466, Fargo, ND 58108

Read the blog at http://stormtrack.areavoices.com/.