A cold season bow echo in a high shear, low CAPE environment: synoptic-scale environment and mesoscale evolution

An intense convective line and subsequent bow echo traversed across the lower Mississippi Valley on 9 March 2006 and was responsible for a number of damaging wind reports across central Mississippi and Alabama. A deep mid-level trough over the central United States was responsible for a particularly intense wind field throughout the atmosphere. Large values of deep layer shear and low-level directional shear were juxtaposed with the location of the convective line and bow echo. Although strong low-level warm air advection was occurring, widespread cloud cover associated with a warm conveyor belt / LLJ feature was prevalent in the pre-convective line environment, which did not allow for any marketable destabilization. The strength of the LLJ ahead of the convective line is of particular interest, where 850-hPa winds exceeded 36 ms-1. Convective instability was only realized very close to the convective line, although CAPE values did not exceed 500 J kg-1. The synoptic environment was consistent with the findings of Burke and Schultz (2004) for cold season bow echo events over the Tennessee and Mississippi Valleys.

The significance of the synoptic and mesoscale conditions will be quantified through climatological anomalies based on NCEP/NCAR Regional Reanalysis Data, and directly compared with additional significant cold season bow echo events as identified by Burke and Schultz (2004). Additional analysis will be performed using high-resolution WRF simulations of the convective line. Preliminary simulations have done a good job in reproducing the convective elements of the squall line. The numerical simulations, along with observations, will be used in an attempt to explain the kinematic and thermodynamic processes within a high-shear, low-CAPE bow echo occurring during the cold season (cold season is defined as 1 October to 30 April).