The unusual Buenos Aires snowfall of July 2007

Buenos Aires lies near the east coast of South America at about 34 degrees S where snow is extremely rare. The only events measured in the city had occurred before 1930. The high latitude causes of the widespread snowstorm of 9th July 2007 are discussed, making it an extraordinary case in light of the historical record. Here, we show that this event can be linked to unprecedented seasonal circulation anomalies in the sub-Antarctic, featuring a dipole around the Antarctic Peninsula that drives the cold advection toward mid-latitudes. Our index suggests that conditions have become more favorable for cold surges over mid-latitudes with a repetition of widespread snow over mid-latitudes in 2009. Copyright (C) 2010 Royal Meteorological Society