3.2
Outstanding issues related to bow echoes and derechoes component of BAMEX
Morris L. Weisman, NCAR, Boulder, Colorado; and R. J. Trapp
Bow echoes and derechoes continue to pose a significant forecast problem over much of the nation. Although there has been much research to date on the dynamics and severe weather potential of these phenomena, there has never been an observational program that has collected sufficient kinematic and thermodynamic data to truly document the lifecycle of these events and to test recent hypotheses as to the critical physical processes involved. Clearly, many outstanding issues still remain. For instance, while most of the arguments proposed to explain the development of severe winds within bow echoes depend on the development of a strong, deep cold pool and associated mesohigh, severe bow echoes and derechoes can occur at night in the presence of a stable nocturnal boundary layer that does not as readily support the generation of the strong surface cold pool. Observational studies also suggest the importance of pre-existing, line-normal thermal boundaries to the formation, propagation, and severe weather associated with bow echoes. Most numerical studies of bow echoes to date, however, have only considered highly idealized environments, characterized by horizontally homogeneous initial states. Issuing appropriate warnings for bow-echo tornadoes is especially problematic. More often than not, there is no readily identifiable supercell signatures or mid-level mesocyclone preceding such tornadoes. The fact that non-supercell tornadoes develop primarily northward of the apex of the bow has not yet been explained. The identification of Doppler radar precursors, such as MARC (Mid-Altitude Radial Convergence), to help forecasters warn for severe wind events, are progressing, but need more detailed datsets to better understand their relationship with severe wind production and to refine its applications. These, and other issues will be reviewed and discussed in the context of planning for BAMEX operations.
Session 3, Bow Echo and MCV Experiment (BAMEX) Symposium
Monday, 12 August 2002, 4:30 PM-6:00 PM
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