A Climatology of Predecessor Snow Events on the eastern Great Lakes

During the winter months, the Great Lakes region is repeatedly affected by lake-effect snow events. These events often occur following the passage of a cold front, as a prevailing westerly or northwesterly wind sets up, resulting in heavy accumulations to the east and southeast of the lakes. However, under certain environmental conditions, this paradigm can be reversed and lake-effect snow can occur on the western sides of the lakes. One way in which this reversal is realized is when air ahead of a warm front of an approaching extratropical cyclone is cold enough as to allow the lake-effect snow to form under easterly flow. This predecessor snow event (PSE) is subsequently exacerbated by synoptic-scale precipitation associated with the approaching extratropical cyclone.

The purpose of this study is to present a climatology of all easterly winter-time wind events over Lakes Erie and Ontario for a 5-year period, encompassing the cold months (November through March) of the winters 2011/12 through 2015/16. An easterly wind event is defined when at least three surface observation stations near one of the two lakes has easterly surface winds for at least one three-hourly period utilizing the Weather Prediction Center’s surface analysis archive. During this 5-year climatology, 130 such events were found. From these 130 events, a more in-depth analysis of those associated with lake-effect snow will be discussed. Preliminary results indicate that there were 20 such events during this time period, with the majority (17) of them being characterized as PSEs with an extratropical cyclone approaching from the central Mississippi Valley coupled with an Arctic anticyclone centered over southern Quebec producing easterly flow over the eastern Great Lakes region. Environmental conditions such as inversion height, 850-hPa temperature, lake temperature, boundary-layer shear, and boundary layer wind speed will be analyzed to determine common conditions associated with these PSE events.