A series of hourly mesoscale analyses detailing the evolution of
surface features prior to and during the 27 May 1997 central Texas
tornado outbreak will be presented. It will be shown that the initial
thunderstorms formed near Waco along a nearly stationary
northeast/southwestoriented dry line, at the time the feature was
being overtaken by a slow moving cold front. The simultaneous
approach of an undular bore-type internal gravity wave, traveling
southwest across the region, also appeared to play a role in
convective initiation. The wave was formed by an overnight MCS in
Arkansas and moved nearly perpendicular to the merging boundaries
over central Texas. Evidence will be presented to suggest that the
gravity wave was influential in not only triggering the first storms,
but also in modulating the development of new cells southwest of the
initial activity. It will also be suggested that as the wave
continued southwest and encountered a region where it was oriented
more parallel to the boundaries over south Texas, thunderstorms
simultaneously erupted along the remaining portion of the boundaries.
Given the close proximity of adjacent convective cells in this
region, and the presence of steep lapse rates and mid level dry air
to support down draft development, this activity quickly evolved into
a damaging bow echo, in contrast to the supercellular convection
which prevailed farther north.