The June 2013 Flood-producing Extreme Rainstorm over Southern Alberta

A devastating flood-producing rainstorm occurred over southern Alberta, Canada during the period 19-22 June 2013. The long-lived heavy rainfall event was a result of complex interplays between topographic, synoptic, convective processes, which rendered the accurate simulation of this event a challenging task. The Weather Research and Forecasting (WRF) Model was used to simulate this event and the simulated precipitation is evaluated by comparison with several observed datasets. Results show that both the timing and location of the model precipitation agree closely with the observations, indicating that the WRF model is capable of reproducing this type of severe event. The model diagnoses show that most of the precipitation were produced by orographic lifting, mid-troposphere cyclonic vorticity advections and lower tropospheric frontogenesis. The HYSPLIT back trajectory analysis and regional water budget assessments using WRF simulation outputs suggested that the moisture for the precipitation was mainly from regional scale moisture convergence by advection across a significant part of the continent, especially the recycling of the antecedent soil moisture through evapotranspiration over the Canadian Prairies and US Great Plains. A small part of the moisture can be traced back to the northeastern Pacific but direct uptake from the Gulf of Mexico was not a significant source of moisture.