The past six months or so have been punctuated by a series of extreme weather events in North America, from strong winter storms to rapid snow melt to tornadoes of unusual intensity, most recently in Massachusetts, far from their typical range.
Often such anomalies are ascribed to El Niño events -- accumulations of unusually warm water in the equatorial Pacific the prior December -- or La Niña, the opposite. According to NASA Science News, however, the 2011 events seem to result from an unusually free-wheeling jet stream, which in turn results from "La Nada" -- a lack of a strong Pacific temperature signal in either direction.
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