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

The effects of the Great Lakes on deep convective systems are poorly known. This can create a complex problem for forecasters responsible for areas over or downwind of a lake, as it is uncertain how storm intensity and structure will be affected by passage over the water surface. This paper describes results of one component of a Cooperative Program for Operational Meteorology, Education, and Training (COMET) project that seeks to improve understanding and forecasting of convective systems crossing Lake Erie.

WSR-88D radar, surface, buoy, and rawinsonde observations collected from 2001-2009 were used to characterize atmospheric conditions upwind of the lake and within the marine boundary layer (MBL) as well as storm behavior over Lake Erie. In total, 111 cases of pre-existing convection (>45 dBZ) moving over Lake Erie during the 9-year period were identified. Of these storms, 30 were classified as ‘clusters', 25 ‘isolated', 34 ‘linear' and 22 ‘complex.'

Analyses revealed that noteworthy systematic changes in the maximum reflectivity of the systems were generally not observed until 60 minutes over the water. Cluster and isolated systems tended to weaken in cases where the MBL was convectively unfavorable (i.e. reduced surface-based instability), while linear and complex systems tended to be less affected by the MBL, regardless of its characteristics. Linear correlations between the various environmental parameters and changes in maximum reflectivity of the convective system were generally weak, suggesting that no single parameter fully explained the observed storm behavior over the lake. However, isolated systems showed a statistically significant correlation between storm weakening and colder over-lake surface air temperature conditions. Analysis of linear systems indicated a statistically-significant weakening trend as low-level (3 km) vertical wind shear decreased. The results of statistical analyses of parameter/storm intensity relationships, including multivariate and non-linear analysis, as well as an individual case study examining the effect of the MBL on a mature squall line, will be presented.