A climatology of freezing rain in the Great Lakes region of North America

A 15-yr climatology of freezing rain surrounding the Great Lakes region of North America has been constructed using data from rawinsondes, surface stations, and gridded reanalyses from the National Centers for Environmental Prediction. This climatology reveals that there is a general increase in the freezing-rain frequency from west to east; however, the distribution shows large spatial and temporal variability. Most freezing-rain events are short lived and occur near sunrise between the months of December and March. Continuous freezing rain typically lasts less than 1 h, with 7% of events lasting longer than 5 h. Most freezing rain is associated with extratropical cyclones, occurring northeast of the cyclone center in the presence of midlevel upward vertical motion, and air that is nearly saturated at low and midlevels, subfreezing near the surface, and warm (>0 degree C) at low levels ( approximately 850 hPa). The location of the mean extratropical cyclone track during freezing-rain events in the Great Lakes region east of 87 degree W and the climatological cyclone track during January partially explains the eastward increase in freezing-rain frequency. Additionally, it appears that the proximity of the Atlantic Ocean to the area east of 81 degree W provides a large moisture source for these events, while western events appear to receive moisture from the distant Gulf of Mexico. The Great Lakes appear to have some effect on reducing the occurrence of freezing rain very near the western shores.