An Overview of the Historic 19-20 June 2012 Flash Flood Event in Duluth, MN and Adjacent Areas of Northern Minnesota and Northwest Wisconsin

Historic heavy rains and flash flooding affected a large part of northern Minnesota and far northwest Wisconsin on 19-20 June 2012. Widespread rainfall amounts exceeding 6 inches fell over much of east central and northeast Minnesota, and adjacent parts of far northwest Wisconsin, with a large geographic area centered near Duluth, MN receiving in excess of 8 inches of rain in less than a 24 hour period, and maximum measured storm-total rainfall amounts up to 10.10 inches. Precipitation analysis of this event from the Duluth, MN observing site indicates 9 separate time periods between roughly 4 PM June 19 through 12 PM June 20 where 1-minute rainfall rates exceeded 3 inches per hour for a time. For northern Minnesota, such rainfall rates and amounts are estimated to have annual probability of occurrence of less than 0.3 percent, and an approximate return period between 300 and 500 years. The combination of heavy storm total rainfall and intense rainfall rates led to severe flash flooding across much of east central and northeast Minnesota and far northwest Wisconsin, including the Cities of Duluth, MN and Superior, WI. Within the City of Duluth, preliminary storm damage estimates exceed $100 million as of mid July 2012.

This presentation will discuss the scientific aspects of heavy rainfall and flash flood processes during this event, and the unique operational and topographic challenges presented by the terrain in the severely affected areas. In addition, this is perhaps the most significant heavy rain/flash flooding event not driven by a tropical weather system in the continental U.S. to yet be observed by an operational polarimetric WSR-88D radar, and we will present a preliminary assessment of the performance of KDLH dual-pol radar data during this event. Finally, we will also briefly discuss significant river flooding that persisted for 2 weeks in the aftermath of this event, and the long-term impacts to infrastructure, transportation and the recovery process across the region.