In this event, which occurred ahead of Tropical Storm Erin, a southerly stream of deep tropical moisture (precipitable water values >50 mm) moved poleward and intersected a northwest-to-southeast oriented quasi-stationary baroclinic zone beneath the equatorward entrance region of an upper-level jet streak over the upper Midwest. A slow-moving convective system developed and produced widespread heavy rainfall, with local amounts exceeding 380 mm (15 inches) that resulted in destructive and deadly flooding in Minnesota and Wisconsin. Observations and numerical simulations using the Weather Research and Forecasting (WRFARW) model indicate that low-level frontogenesis was maximized during the overnight hours of 19 August 2007 and provided the forcing for vigorous ascent during the mature stage of the PRE. A simulation in which the moisture attributable to TS Erin was removed shows a 25% reduction in the total precipitation and a 50% decrease in the maximum precipitation over the PRE region compared to the control simulation. The extent of this decrease in total precipitation in the dry run underscores the importance of moisture originating from TS Erin in transforming a heavy rain event into a high-impact, record-breaking rain event.