Student Seminar Series
Department of Atmospheric & Oceanic Sciences
a talk by
Synoptic-dynamic and thermodynamic conditions distinguishing long- and short-duration freezing rain events
Freezing rain can have devastating impacts, from dangerous road conditions to tree and power line damage leading to long-lasting power outages. Still, freezing rain remains a major forecast challenge. Because of its typically light intensity, the severity of a freezing rain event is closely related to its duration. Most freezing rain events persist only for a few hours, as the diabatic processes associated with phase changes in the above-freezing warm layer aloft and near-surface below-freezing cold layer act to destroy these layers. For freezing rain to persist for many hours, compensatory mechanisms such as cold-air advection in the cold layer must be present to offset these diabatic effects.
Here, we examine the thermodynamic and synoptic-dynamic characteristics impacting freezing rain event duration over the United States and Canada using surface and upper-air observations from 1979–2016. Upon identifying freezing rain events at 579 surface stations, we perform a comparison of the thermodynamic profiles observed at the onset of long-duration (6 or more hours of freezing rain) events with those that have led to less-severe short-duration (2-4 hour) events. In this presentation, we focus on the south-central United States, where a disproportionately high number of extremely long duration (18+ h) freezing rain events have been observed relative to the frequency of freezing rain overall there. Through an examination of synoptic composites produced for each event type, we identify key differences in the patterns leading to prolonged events and those that result in only short-duration cases.
Wednesday Jan 22/ 2.30 PM/ Room 934 Burnside Hall