First Alert Weather In-Depth: It is an atmospheric river

ROCHESTER, N.Y. – This is weather terminology that is not heard very often here in Rochester. It is called an “atmospheric river.” This is a concentrated, narrow band of high density moisture that is focused off of the Pacific Ocean and can stretch for over a thousand miles. This moisture plume comes into the California area and has been ongoing for several weeks. This atmospheric river has been intensified by a series of storms that helps to drive a lot of that moisture right into California.

Believe it or not there is a positive side to this event. The benefit is the huge amount snow falling in the Sierra Mountains. Remember, the folks out west have been in a drought for the last decade, but portions of the Sierra Mountains have measured almost twice as much snow, compared to their usual snowfall for this time of the year. No doubt they will need much more in the coming season, but this will go a long way to improve the dry conditions for the short term.

However, there is a negative side to all of this precipitation and some people would say it is too much of a good thing. Heavy, torrential rainfall in the lower elevations is producing mudslides and road closures. For example, San Francisco got a near record amount of rainfall with thousands of evacuations due to flooding.  And they could receive another 8 inches of rain in the coming days which would obviously expand the flooding.