MCS Initiation and Development Influenced by the Land/Lake Thermodynamic Contrasts near the Great Lakes

One of the primary considerations for the impact of the Great Lakes on MCS development is the (potential) temperature gradient close to the surface across the land/lake boundary. Rotunno et al. (1988; hereafter RKW) have shown that the balance between a convectively-generated cold pool and low-level shear determines the structure of quasi-linear MCSs. The addition of a dome of relatively cold air over the lake surface would alter the RKW cold pool/shear balance and could thus be important to the intensity and structure of convection as it approaches, traverses, and leaves the lake. If the cold dome over the lake can develop into a deep near-surface cold layer, the resulting effect may approach the scale and magnitude of the cold pool generated by an MCS. At any point in the development of lake-influenced MCSs, the depth of the cold dome over the lake (especially when compared to the depth of the MCS-generated cold pool) should be an important consideration.

This study will focus on a climatology and selected case studies of MCSs that form and intensify as a result of the presence of the Great Lakes. Upstream of the lake, the combination of forcing for ascent by the lake's cold dome and a pre-existing cold pool could cause especially strong lift between the surface cold regions. Later, the conglomeration of an MCS cold pool and a lake-generated cold dome could cause the convection to weaken and/or become elevated (as the near-surface air is too stable to lift). Downstream of the lake, convection moving off the cool lake would have an apparent cold pool in place, which could lead to MCS (re)development more rapidly into the optimal or mature stage (as defined in RKW). It will be shown that the shear profile and the balance of both the lake and MCS cold pools are important for diagnosing the nature and longevity of MCSs influenced by the Great Lakes.