Radar observations of lake breezes in southern Manitoba, Canada

Lake breezes are thermally direct circulations that form as a result of the differential heating of land and water surfaces. While these events are generally well understood, studies on smaller lakes have been relatively scarce, and none have examined lake-breeze circulations in southern Manitoba. Lake breezes can have strong influences on the local climate, ranging from influencing meteorological conditions, to lake-breeze fronts acting as triggers for convective storms. The objectives of this paper are to provide a radar-based climatology of lake-breeze fronts and characteristics, an assessment of the different types of lake-breeze circulations, and the meteorological conditions in which they occur. Between 2008 and 2013, 205 lake-breezes fronts were noted on radar in southern Manitoba over the summer months (JJA) accounting for 37% of study days. Lake- breeze fronts were detected most frequently on Lake Manitoba, in particular along its eastern shore. Lake breezes were found to occur on average on 11-12 days of each month (JJA). These findings agree well with reported frequencies for other lakes in North America such as the lakes within the Great Lakes region, though are lower than most recent findings in southern Ontario. In an effort to validate these findings, a broad comparison between the radar analysis and a more complete analysis using satellite and surface stations is provided for 2013, which demonstrated that radar is more accurate for detecting breezes around Lake Manitoba than around Lake Winnipeg.Lake-breezes circulations originating on Lake Manitoba and Shoal Lakes were classified into three types according to the circulation types developed by Sills et al. The distribution of types for Shoal Lakes was found to be similar to that reported by Sills et al., with ‘moderate deformation' circulations being the most frequent. Finally, a brief meteorological analysis was completed for each day of this study. Wind direction and wind speed appeared to have a higher correlation with the frequency of lake breeze events as compared to other limiting factors such as temperature or precipitation days.