Observed Bow Echo events during the first week of July 2003 concurrent with BAMEX

The first week of July 2003 saw three 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. 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. The purpose of this presentation will be to discuss storm-environment interactions during the three bow echo events.

These complex interactions occurred on both the synoptic and mesoscale during each event. Although each case differed in some respects, the cold pool created from each MCS and resulting outflow boundaries helped to focus and initiate new convection the next day. In addition, preliminary results show that the Great Lakes influenced the bow echoes leading to both convective intensification and weakening depending upon the conditions. Fortuitously, these three bow echoes occurred during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). This allowed for unparalleled observation of these interactions as careful forecasting occurred throughout the lifecycle of the events. Analysis of the radar data, along with model forecasts, satellite imagery and surface observations contribute to an understanding of both the synoptic and mesoscale environments present in the upper Midwest during this week. Additional observations from P-3 aircraft as well as dropsondes released in the vicinity of the bow echoes augment the other data.