Wednesday, November 28, 2012

California Flood Threat

While it is not an ARkstorm, California will be falling victim to an "atmospheric river" which is expected to cause extensive flooding this week. From Weather.com:
Meteorologists use the term "atmospheric river" to describe a long, narrow plume piping deep moisture from the tropics into the mid-latitudes. . . .

Amazingly, according to NOAA's Earth System Research Laboratory (ESRL), a strong AR can transport as water vapor up to 15 times the average flow of liquid water at the mouth of the Mississippi River!

Suffice to say, if an AR stalls over a particular area, significant flooding can be the result. . . . 

. . . The soaking starts Wednesday as the initial frontal system sweeps into the West Coast.

This first system should be a quick mover. While rain and high-mountain snow is forecast primarily for California, but also into western Oregon and parts of western Washington, precipitation amounts Wednesday should be relatively "routine", for a Pacific frontal system in the wet season.

Then, the "atmospheric river" makes landfall.

Beginning Thursday, the upper-level pattern will begin to tap into an atmospheric river of moisture extending from just north and west of Hawaii to the West Coast.

Most importantly, that plume of moisture won't move appreciably for a couple of days, perhaps through Sunday, aiming its firehose of moisture at northern California and, perhaps, southwest Oregon.

Therefore, some locations, particularly in the coastal ranges of northwest California and the Sierra foothills, will likely pick up over 10 inches of total rainfall through this weekend, leading to flash flooding, river flooding and, in recent burn areas, debris flows.

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