Tuesday, 13 January 2004
Learning from a null derecho event—the convective forecast for 08 July 2003
On the late evening of 07 July, 2003 and the early morning of 08 July, 2003, several favorable atmospheric parameters were in place to support the development of a long lived and widespread bow echo event (derecho) over Nebraska, yet some parameters were absent. The event did begin with severe thunderstorms initiating over western Nebraska, but rapid dissipation followed the development of the severe storm complex. This resulted in a "null event" for a severe weather outbreak, and it is worthy of close examination. This event did not evolve as many forecasters anticipated. Often case reviews are conducted for those events in which significant severe weather occurred, but little attention is given to those events that resulted in a false alarm. Much can be learned from studying these null events, and the end result is a greater understanding of the conditions that are required for the positive occurrence of the severe weather events.
This paper will go into detail reviewing the environmental surface and upper air parameters, as well as the resulting observed storms from a radar perspective. Earlier works will be referenced to compare the parameters with this event to the suggested parameters specified by other researchers. A clear picture of why this event did not materialize will be presented, with the primary goal of pointing out those environmental parameters that need to be present for derecho development but were not present for this event. If forecasters have a better understanding of the necessary ingredients, and a more complete conceptual model of environments that do support, and do not support derechoes, more accurate predictions of these phenomena should result.