Severe thunderstorms and Flash Floods over Southwestern Québec on May 29th 2012

On May 29th 2012 a number of lines of severe thunderstorms formed along, and in front of an important cold front in Southern Quebec. Approximately 70 mm of rain fell on downtown Montreal in one hour causing flash flooding. Hail with a diameter of two inches was reported in the Montérégie and damaging wind gusts occurred in the Upper Gatineau, suburban Montreal and areas close to the New York state border. This poster will look at the analysis process from the forecast desk on that day, including the evaluation of the air mass leading up to the storms, radar sequences from the most intense cells and the timing of watch and warning bulletins. Some local aspects which contributed to the intensity of these storm cells are also investigated, including a stationary convergence zone along the Saint-Lawrence river valley.