Utilizing established techniques in forecasting the potential for derecho development

An analysis of the long-lived,damaging wind event of 20 April 1996 is presented. This case study is an example of a "dynamic" long-lived bow echo event, or derecho. The Johns and Hirt 1987 Derecho checklist and parameters gained from the 1992 Duke and Rogash "dynamic" derecho study have been examined to show that these parameters can be used operationally to determine the potential for a long-lived severe wind event.

The 20 April 1996 long-lived bow echo event was part of a large severe weather outbreak that originated in eastern Iowa, Illinois and southeast Missouri during the afternoon of 19 April 1996. During the early morning of 20 April 1996, a line of severe thunderstorms continued their southeast movement into northwest Tennessee and moved rapidly eastward, causing extensive wind damage as it progressed across middle and east Tennessee.

This paper will show that the potential for this type of widespread wind event can be recognized, with early recognition being better utilized to inform the public of the possibility of impending severe weather. Early recognition of this type of damaging wind event can lead to the issuance of a Hazardous weather outlook to highlight the possibility of severe weather. The initial issuance of the Hazardous weather outlook (Special Weather Statement), around eight hours in advance of this particular event gave local emergency management officials, local media and residents time to prepare for the possibility of this severe weather event.

Although this was a continuation severe weather event, the use of the Johns and Hirt Derecho checklist and severe weather parameters gained from the 1992 Duke and Rogash "Dynamic" derecho study were used by forecasters to aid in the pattern recognition of this long-lived damaging wind event around eight hours before the event occurred. This project was developed to aid forecasters in the detection of future long-lived bow echo events in the lower Ohio and Tennessee valleys.