Heavy snow climatological research at NWS Louisville is being conducted as part of a COMET Cooperative Research Project between NWS Louisville, NWS St. Louis, and Saint Louis University (SLU). Our specific goal to develop seasonal heavy precipitation climatologies over the middle Mississippi and Ohio River Valley. This goal is a large endeavor, requiring review of many past precipitation events in order to develop composite surface and upper-air charts for different types of heavy precipitation producing weather systems during different times of the year. However, this effort is valuable since such climatologies, in conjunction with scrutiny of individual weather systems, ultimately are quite useful to meteorologists in recognizing overall patterns and parameters that typically are conducive to heavy rainfall and snowfall. SLU project members have produced statistical analyses for numerous years of data for warm season heavy rainfall events across Kentucky and southern Indiana. They also have developed various composites of different patterns that produce heavy rainfall in the Ohio Valley. Heavy rainfall events are defined as sufficient coverage of 2 inch or more reports in a 24-hour period.
Meanwhile, NWS Louisville members are focusing on producing a climatology and composite charts for heavy snowfall events for Kentucky and southern Indiana. A heavy snow event is defined as 4 inches or more in a 24-hour period covering a sufficient portion of a state climatological region. We have produced snow statistical analyses for Kentucky and southern Indiana from 1982-1996, and have developed composites of several individual events. From these composites, we have noted at least two significantly different synoptic patterns associated with heavy snowfall across the Ohio Valley. The first pattern consists of relatively weak surface and 500 mb system development. This pattern features a southern stream shortwave within a broad southwest flow at 500 mb, a low-level jet and strong isentropic lift ahead of the shortwave, the presence of a jet streak across the Great Lakes with substantial along-stream wind variation in the entrance region of the jet (i.e., winds accelerate quickly into the jet), and frontogenesis across the Ohio Valley within the right entrance region. The northern jet streak also seems to play a significant role in holding cold air in place across the Ohio Valley despite warm advection from the south. The second pattern is associated with strong surface and upper-air development, including East Coast snowstorms that can bring heavy snowfall to eastern Kentucky, and slow moving closed off lows and deep easterly flow that can lead to significant snow across parts of Kentucky and Indiana if temperatures are cold enough. We will investigate additional individual cases and construct more composites in our research in order to substantiate these findings.
Here, we present preliminary results from our heavy snow climatological research. Click on the various links to view our research results for the specified events.Kentucky and Southern Indiana Climatological Regions; Heavy Snow Statistics (Histograms)