Strong Extratropical Cyclones leading to Noteworthy Cool-Season Extreme Weather Events over Central and Eastern North America

Noteworthy cool-season extreme weather events (EWEs) occurring over central and eastern North America are typically associated with strong extratropical cyclones (ECs) that are governed by varying combinations of baroclinic, diabatic, and barotropic processes.  The opportunity to investigate the ways in which baroclinic, diabatic, and barotropic processes evolve and combine to produce strong ECs motivates this study.  We envision a three-dimensional phase space in which the relative contributions of baroclinic, diabatic, and barotropic processes may be quantified during the evolution of strong ECs, and hypothesize that the majority of strong ECs will cluster along the high ends of the baroclinic and diabatic axes in this envisioned phase space.  A 1979–2016 climatology of strong ECs leading to noteworthy cool-season EWEs over central and eastern North America will be constructed and applicable metrics of baroclinic, diabatic, and barotropic processes will be selected to test this hypothesis using the 0.5° NCEP Climate Forecast System Reanalysis.  The 1979–2016 climatology will be used to identify the combinations of baroclinic, diabatic, and barotropic processes most likely to yield strong ECs over central and eastern North America.

In addition to identifying the combinations of baroclinic, diabatic, and barotropic processes most likely to yield strong ECs over central and eastern North America, the 1979–2016 climatology will be used to establish the importance of geographical location, season, and teleconnection pattern in determining the combinations of baroclinic, diabatic, and barotropic processes most likely to yield strong ECs.  Representative case studies of strong ECs leading to historic cool-season EWEs over central and eastern North America will be presented in this study to illustrate the climatological results.  The "Superstorm" of 12–14 March 1993 (SS93), a strong EC that led to one of the most destructive cool-season EWEs in modern history, will be presented as an example of a strong EC that is hypothesized to form in association with dominant contributions from baroclinic and diabatic processes.  The "November Cyclone" of 9–11 November 1998 (NC98), a strong EC that led to a destructive cool-season EWE in the central and upper Midwest, will be presented as an example of a strong EC that is hypothesized to form in association with dominant contributions from baroclinic processes.  The baroclinic, diabatic, and barotropic processes associated with SS93 and NC98 will be quantified and placed within the context of the envisioned three-dimensional phase space in order to determine the significance of these respective ECs relative to the 1979–2016 climatology.