The 8 May 2009 "Super Derecho": A Land-Hurricane?

December 03, 2009

Morris Weisman (NCAR)

Hosted by Sue van den Heever

Abstract

During the morning of 8 May, 2009, a large bow echo system developed over Kansas and proceeded eastward, producing an extensive swath of severe wind damage from eastern Kansas through southern illinois. During its most intense phase, the bow echo occluded, producing an eye like structure similar in many respects to tropical cyclones. Indeed, much of the wind damage with this system was associated with an intense (10 mb) mesolow located at the tip of the occlusion, well behind the leading gust front. This system was forecast in realtime 24h in advance with the WRFARWmodel, using a 3 km horizontal grid interval, accurately reproducing the observed occluded eyelike structure and accompanying intense mesoslow. This surprisingly accurate forecast allows for an unprecedented analysis of the structure and evolution of such a unique convective system, as well as offering, through sensitivity testing, a sense of the predictability of such events. Preliminary results of this ongoing analysis will be presented, along with comparisons to idealized model representations of such bow echo systems and observations of other significant derechoes.