The violent thunderstorm that struck Potsdam and St. Lawrence County July 17 appears to have been a downburst or a microburst preceded by a gust front. Anna Costanzo photographed the storm billowing up next to Lawrence Avenue Elementary School as she was looking west as the storm moved east. The clouds hanging down are a shelf cloud. (This cutline has been corrected from what was originally posted). For more details on the technicalities of the storm from an expert at St. Lawrence University, click here.