Persistence and Dissipation of Lake Erie- and Lake Ontario-Crossing Mesoscale Convective Systems

Mesoscale convective systems (MCSs) are ubiquitous features across the Upper Midwest during the warm season. Forecasting the evolution of these MCSs becomes difficult as they traverse the Great Lakes. Conventional wisdom suggests that these MCSs might weaken upon crossing the typically cooler waters of the Great Lakes. However, many MCSs have been observed to persist or even intensify upon traversing Lakes Erie and Ontario. Since populated cities are located downstream of the Great Lakes, it is critical to be able to assess whether these MCS will persist or dissipate. This presentation will document environmental and lake characteristics associated with Lake Erie- and Ontario-crossing MCSs in order to ascertain the spectrum of situations under which lake-crossing MCSs persist and dissipate.

Climatological results indicate that of 59 mature MCSs that crossed Lakes Erie and Ontario during the warm seasons of 2002–2007, 26 (44.1%) persisted while 33 (55.9%) dissipated. May was the most common month for MCSs to cross the lakes and was the only month that features more persisting MCSs than dissipating. The large-scale environment offers clues as to whether the MCSs will persist or dissipate. MCSs often persist in environments with robust CAPE and shear downstream of the lakes. In addition, persisting MCSs were often located in the core of an intense 850-hPa low-level jet stream and on the anticyclonic shear side of a strong 200-hPa jet stream. Selected compositing and observational case study results will accentuate the climatological findings in an attempt to highlight the differing combinations of environmental and lake conditions that distinguish between MCSs that persist and those that dissipate.