Wednesday, 14 August 2002
Rapid supercell storm and tornado development along a boundary
A very well documented case study involving the interaction of a pre-supercell storm with a well-defined thermal boundary is examined with a
variety of data sources. The storm developed on the cold side of the
boundary and then intensified upon approaching the boundary from the cold
air side. Rapid storm intensification, accompanied by the development of a
low-level mesocyclone and tornadogenesis occurred as the storm intersected
the boundary. This paper documents the evolution of the boundary and storm
using an array of 15 surface stations, the UAH Mobile Integrated Profiling
System (MIPS), WSR-88D data, and GOES visible imagery. The boundary was
reinforced during the preceding night by evaporative cooling of rain north
of the boundary. The boundary receded northward during the morning hours
from a location just south of the MIPS. Thus, the MIPS provides a good
definition of the boundary structure, and of the boundary layer properties
just south of the boundary. The boundary then remained in a quasi-stationary position within a network of surface stations between 1600-1900
UTC. Solar heating south of the boundary reinforced the strong temperature
gradient, and the flow around the boundary exhibited increasing cyclonic
shear with time. Several minor convective initiation events were
associated with the boundary. Despite its sharp contrast and convergent
nature, it was not well depicted in GOES visible imagery. In this case
there is sufficient surface data to estimate gradients in kinematic and
thermodynamic properties over the mesoscale domain where the supercell
storm evolved.
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