Grant: Engage Plus Grants Program

The Weather Network provides radar-based six hour nowcasts on their web site, based on extrapolation of radar imagery. The aim is to evaluate and improve the performance of these forecasts which use a version of MAPLE (the McGill Algorithm for Prediction by Lagrangian Extrapolation). One goal in Phase I has been to see over what lead time, under various circumstances, nowcasting procedures give reliable results. In Phase I we are focusing on the southern Ontario region where lake effects can strongly influence winter snowfall.Depending on the circumstances forecast reliability varied from 1-6 hours but with lake effect snow squalls, which generally remain in a relatively fixed location, MAPLE tends to advect them away and forecast reliability is poor.In Phase I we are evaluating and testing ways in which these nowcasts could be improved through better determination of advection velocities and storm cell evolution and by a better understanding of the role of lake effects. This can lead to more accurate determinations of the location and intensity of precipitation. In lake effect snow squalls individual cells generally form over water, travel downwind and decay over land and the area of precipitation is more or less stationary. We find that careful adjustment of some of the parameters used within MAPLE could improve performance in these cases, and we are developing methods to handle such features, and thus give longer lead times and improved and better defined forecasts for heavy winterprecipitation. The aim in Phase II will be to extend this work to summer precipitation events, both in the Great Lakes area butalso in areas near the Rocky Mountains where orographic effects can also lead to stationary precipitation patterns.