Climatology of Fronts and Associated Surface Baroclinic Zones in the Great Lakes Region

Frontal and trough passages over the Great Lakes are a critical factor in influencing weather in the region. For example, fronts often have a significant role in the initiation and evolution of severe thunderstorms, winter storms, and lake-effect snow storms. A six year climatological study was undertaken to understand the spatial distribution and temporal frequency of fronts and troughs in the region. National Center for Environmental Prediction (NCEP) surface analyses and North American Regional Reanalysis data were used to determine the frequency of different frontal types in relation to each of the Great Lakes and the association of baroclinic zones relative to analyzed fronts. Frontal locations and evolution were determined by examining the six-hour surface analyses (00, 06, 12, 18 UTC) for January 2000 through December 2005. A total of 2,173 fronts and 1,075 troughs were identified during the six year period investigated. Cold fronts were the most frequent frontal type, followed by stationary, warm, and occluded fronts, respectively. Lake Michigan experienced the highest number of frontal passages while Lake Ontario experienced the least. The analyses also provide information regarding the intra-annual and interannual variability of fronts and troughs.

Surface baroclinic zones were identified using two-meter potential temperature analyses. Our investigation identified the presence of both strong and moderate surface baroclinic zones defined as having a potential temperature gradient between 3.5 and 7.0 °C (100 km)^-1 and greater than 7.0 °C (100 km)^-1, respectively. Approximately 50% of the fronts in the Great Lakes region were associated with moderate or strong surface baroclinic zones, with very few fronts associated with strong baroclinic zones. Warm and stationary fronts were the frontal types most often coupled with baroclinic zones. Troughs were subdivided into synoptic, sub-synoptic, and mesoscale troughs. It was found that synoptic-scale troughs generally were not associated with baroclinic zones, while mesoscale troughs were more often associated with moderate and strong baroclinic zones.