Tuesday, 25 October 2005
Alvarado F and Atria (Hotel Albuquerque at Old Town)
The first week of July 2003 saw four separate bow echo events propagate across the upper Midwest. The environment ripened for convection as moisture pooled along baroclinic zones, leading to surface dewpoints in excess of 20∞C. Warm advection and the associated isentropic upglide over the baroclinic zones allowed for continued moisture infusion. Steep mid-level lapse rates, along with daily diabatic heating allowed for destabilization of high CAPE atmospheres as each day progressed. In each case, shortwave disturbances helped to strengthen the upper-level flow, which aided in the generation of bow echoes once organized mesoscale convective systems (MCSs) developed. Additionally, potential vorticity anomalies were present, providing another dynamical contribution to the environment. Deep layer shear in excess of 40 knots favored bow echo evolution throughout the time period. During each event the intensification of the nocturnal low-level jet further enabled high equivalent potential temperature/CAPE (surface based) air to accelerate poleward where it was intercepted by the eastward traveling MCSs. As a result of a combination of these factors, the upper Midwest saw extensive wind damage during this period associated with the bow echoes.
Bow echoes are often thought of in an idealized sense. However, complex interactions occurred on both the synoptic and mesoscale with each event. This led to a unique radar representation in each of the separate cases as different dynamic and thermodynamic factors coexisted. In addition, preliminary results show that the Great Lakes influenced the bow echoes, at some times leading to intensification and others to weakening. Fortuitously, these four bow echoes occurred during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX), three of which took place during intensive observing periods (IOPs). This allowed for unparalleled observation during the events of these interactions as careful forecasting took place throughout their lifecycle.
Radar composites will be presented for each of the bow echo events. In addition, model forecasts, satellite imagery and surface observations that enhance the analysis of the radar data will be utilized. Supplementary observations from P-3 aircraft as well as dropsondes released in the vicinity of the bow echoes augment the other data. These all contribute to an understanding of the synoptic and mesoscale environments present in the upper Midwest during this week, which allows for each distinctive bow echo to be examined in great detail. http://www.atmos.albany.edu/student/nmetz/ABQfigures.html
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