High impact weather events are defined as hurricanes, tornadoes, hail, high winds, droughts, floods and flash floods and severe general storms. Recent examples of these events include the Atlanta floods of 2009, the May Day 2010 severe flash flood and tornado assault on Memphis, Tennessee and the concurrent flash flooding of central Tennessee and Kentucky and the April 26/27, 2011 concurrent tornado and flooding events . The flash flooding and tornado events in northern Arizona in October 2010 preceded the major tornado, high winds and flooding of October 26-27, 2010 as "a meteorological bomb" storm developed over the northern Mid-West and then traversed the country.

Less than one year later the epic spring snowmelt flooding in the Central United States produced significant flooding along the Mississippi River. As the flood head reached the South, its arrival coincided with the deadly April 27, 2011 tornado outbreak. In turn, the tornado outbreak was preceded by a night of severe thunderstorms with high winds and flash flooding rainfall. The storms cut electrical power used for communications and siren warning in several communities impacted by the deadliest tornadoes. Fortunately cell and smart phones managed to bridge some of the communications gaps but not all.

Final example is the recent passage of Hurricane and Tropical Storm Irene up the East Coast and into New England. Again this hurricane wielded multiple assaults with high surf, high winds, severe weather and catastrophic flooding. In many cases communities were simply overwhelmed by the event when it occurred. However social media played a role in passing warnings other media were not able to accomplish.

The hallmark of these high impact weather events is that concurrent severe weather events occurred with severe or major riverine flooding. Most hazard mitigation and community response plans focus on the singular occurrence of different forms of high impact weather not the concurrent occurrence of several forms of events. These high impact events should provide the impetus for the development of emergency response decision support systems that tie together weather prediction, communication of the threat and community response actions.

This paper will evaluate the timing and types of severe weather events that concurrently occurred and produced a high stress on the emergency management community.