From Michelle Williams, NASA's Goddard Space Flight Center

Though the summer heat and humidity makes it seem like a lifetime ago, the record-breaking snows in the eastern U.S. last winter are not something we will soon forget. Several feet of powder fell on most of the Mid-Atlantic region during February 2010, and a study from Columbia University’s Lamont-Doherty Earth Observatory gives us new insight into what caused the freaky weather.

A rare combination of weather — not climate — patterns seems to be the culprit. El Niño produced abnormally wet conditions in the southeastern U.S.; a negative North Atlantic Oscillation pushed frigid Arctic air down from the North. This collision of moisture with abnormally cold air led to more than six feet of snow over the region between December 2009 and February 2010.

The visualization above, derived from the Goddard Earth Observing System Model Version 5 (GEOS-5) and created by NASA Goddard's Scientific Visualization Studio, shows the first wave of the February snowstorms hitting the East Coast about four seconds into the animation. The second wave forms off the west coast of Mexico's Yucatan peninsula — about twelve seconds in — and then pummels the East Coast.

Cross posted and adapted from NASA’s What on Earth blog. Michelle is based in Washington, D.C.