J5.9 A climatological analysis of deep convection interactions with the Lake Erie marine boundary layer

Wednesday, 4 August 2010: 12:00 AM
Red Cloud Peak (Keystone Resort)
Thomas E. Workoff, Systems Research Group, Inc. and NOAA/NCEP/WPC, College Park, MD; and D. A. R. Kristovich and N. F. Laird

The effects that the Great Lakes have on deep convective systems are poorly known. This study examines the effect that Lake Erie, and its corresponding marine boundary layer (MBL), have on pre-existing convective storms which propagate over the water surface. To do this, data collected from the 2001-2007 period was analyzed to identify trends in storm behavior over Lake Erie based on season, time of day, convective type and changes in surface-based atmospheric instability due to the lake.

Results of the climatological study identified 89 cases of pre-existing convection (>45 dBZ) that moved over Lake Erie during the 7-year period. Of these storms, 24 were classified as ‘clusters', 20 ‘isolated', 27 ‘linear' and 18 ‘complex.' The evolution of each type of convective system, depicted by changes in the storm's maximum base reflectivity after spending 30 and 60 minutes over the water, was related to environmental parameters characterizing the change in surface conditions over Lake Erie. These parameters were created from hourly surface observations in an effort to measure changes in the surface characteristics of the boundary layer from land to lake, as well as estimate MBL stability, among others.

Analyses revealed that noteworthy systematic changes in the maximum reflectivity of the systems do not occur until 60 minutes over the water. Additionally, cluster and isolated systems tend to weaken in cases where the MBL is convectively unfavorable (i.e. reduced surface-based instability), while linear and complex systems tended to be less affected the MBL, regardless of the MBL conditions. Correlations conducted between several parameters and maximum reflectivity change suggest that no one parameter is the cause of the observed storm behavior over the lake, although linear systems showed high correlation of storm weakening in cases of small low-level (2.5 km) vertical wind shear. The results of statistical analyses of parameter/storm intensity relationships, as well as an individual case study examining the effect of the MBL on a mature squall line, will be presented.

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