Wintertime Air Parcel Trajectories for Great Lakes Five-Lake Lake-Effect Days

Surprisingly little is known about the origination and movement of air masses that lead to cold-season lake-effect development in the Great Lakes region. This study examines air parcel trajectories connected to air masses that cause lake-effect cloud bands over each of the five Great Lakes on a single day. These five-lake lake-effect (5LE) days can have substantial impacts on residents of the Great Lakes region from the widespread lake-effect conditions. A database of identified lake-effect days was used to select 166 5LE days during the 20 winters of 1997/98 – 2006/07, which made up 18.4% of all winter days within that time period. NOAA’s HYSPLIT model was used to create a 27-member ensemble of 120-hour back-trajectories starting over each of the Great Lakes on every 5LE day to examine the origination and movement of air parcels that led to lake-effect over each lake. North America and adjacent oceanic regions were divided into 11 different subregions to examine the large number of parcel pathways during the 166 5LE days. Air parcel origination 120 hours prior to a 5LE day was highly variable: over 50% of air parcels started in the Northwest region while regions including Hudson Bay (20%), Greenland (10%), and the American West (10%) contained most of the other parcels. While the origination region can notably vary with respect to 5LE day and lake, there is limited variability of air parcel origination and movement pathways from month to month during the winter.