The Utility of Additional Soundings for Forecasting Lake-Effect Snow in the Great Lakes Region

Abstract

The impact of initializing a mesoscale model with additional sounding data over the Great Lakes region is investigated. As part of the Lake-Induced Convection Experiment (Lake-ICE) field study during the winter of 1997/98, six supplementary Cross-chain Loran Atmospheric Sounding System (CLASS) units and three Integrated Sounding System (ISS) units were used in addition to those from the standard synoptic upper-air network. The three ISS units were in the vicinity of Lake Michigan, and the six CLASS units were in the data-sparse region of central and northeastern Ontario and western Quebec. The Pennsylvania State University?National Center for Atmospheric Research fifth-generation Mesoscale Model running on a doubly nested grid is used to simulate the lake-effect snow event of 4?5 December 1997. This model output from a 30-km horizontal resolution grid shows that the six CLASS soundings capture a warm layer below 850 hPa that appears to be the result of diabatic heating from the Great Lakes. This leads to an improved simulation of the surface pressure fields over the course of the simulation. A nested 10-km horizontal resolution grid shows that the initialization data from the CLASS sites seemed to have a greater influence on the propagation of a mesoalpha-scale trough that caused significant snowfall to the lee of Lake Michigan than data from the ISS sites. The inclusion of the CLASS sounding data changes the track of the precipitation maximum by approximately 25 km and agrees better with reflectivity data from the Weather Surveillance Radar-1988 Doppler. Implications for forecasters in the Great Lakes region are discussed.