December 2, 2012 - Northern California
is experiencing the first days of what weather forecasters are warning will be a long series of torrential rainstorms that could cause serious flooding across the northern one-third of the state. The relentless storms are being driven by a feature in the atmosphere you have probably never heard of: an atmospheric
Oh, and another atmospheric river created the worst flooding since the 1960s in western England and Wales
this past week, where more than 1,000 homes had to be evacuated.
An atmospheric river is a narrow conveyor belt of vapor about a mile high that extends thousands of miles from out at sea and can carry as much water as 15 Mississippi Rivers. It strikes as a series of storms that arrive for days or weeks on end. Each storm can dump inches of rain or feet of snow. For more details, see this feature story that Scientific American
has just published, written by two experts on these storms.
Scientists discovered atmospheric rivers in 1998 and have only recently characterized them fully enough to allow forecasters to warn of their arrival. They can strike the west coasts of most continents, but California
seems to be a prime target.