Synoptic Patterns Associated with Northeast and Southeast Ice Storms

Abstract:

Wintertime storms that produce precipitation events such as snow, freezing rain, and ice pellets cause significant damage to utility services and disrupt travel. These synoptic systems involve deep isothermal regions where warm, moist air over-runs surface sub-freezing air. However, little else is known about the synoptic evolution of the storms. Therefore this study analyzes the dynamic and thermodynamic conditions of ice events along the east coast.

The National Climatic Data Center (NCDC) Storm Events Database is used to pull the dates of ice events from the Northeast and Southeast climate regions for 1996-2013. We find that Southeast ice storms often cover a large geographical region, while Northeast ice storms tend to be much smaller but more frequent. We utilize Geographic Information Systems (GIS) to relate the spatial coverage of our ice events to population density in order to compare the impacts of the events in the two regions.

Next, we analyze the synoptic control of ice storms from both regions in an effort to explain what causes the size differences. For the ice storms gathered from the Storm Events Database, composites are generated for sea level pressure, 2-meter temperatures, 850-hPa temperature and 850-500 hPa thickness, and vorticity parameters, from reanalysis data. A comparison of the composites for the Southeast and Northeast storms suggests that the size differences relate in part to the thermal structure produced by cold air damming. The ice events are also associated with objectively identified cyclone tracks, and we find that cyclone forward speed is inversely proportional to the size of the ice storm produced.