Abstract
A primitive equation model was utilized to describe the initial fields of atmospheric motion, temperature and humidity for the case of a snow-squall situation over Lake Ontario. Of primary interest in this study is the initial vertical velocity field which was obtained through solving a three-dimensional vertical velocity equation. Conventional surface mad upper winds and geopotential heights for ten isobaric surfaces were plotted on a large area base map and subjectively analyzed. Then these analyses were transferred to a local area base map for Lake Ontario. Initial data consisted of winds over the region of interest and geopotential heights on the boundary.
The model produced initial vertical velocities that were consistent with the commonly associated features of the reported weather, and also with some earlier subjective estimates. Analysis of the vertical velocity field revealed that the ascent over the south-central side of the lake resulted primarily as a consequence of the imbalance between the configurations of the thermal stability and advection fields. Latent heat of vaporization released from condensation caused by the large-scale ascent also helped to intensify the mesoscale vertical velocities. Further analysis of the vertical velocity disclosed that the initial intensity at 900 mb was not very sensitive to orography.
