A Lowtop, HP Supercell in West Virginia


A goal of SWAT has always been to search out unique, tornado-producing thunderstorms from all regions of the U. S.  We were excited to discover this storm in West Virginia that we have termed a lowtop-high precipitation (lowtop HP) supercell.  The storm occurred in early January with a low tropopause, and it exhibited a very unique morphology.  The storm persisted for about three hours, and resulted in two tornadoes and three severe wind reports.

Tests of the NSSL algorithms on this data have yielded very favorable results.  Presented here are various WSR-88D radar images from the Charleston, WV (KRLX) radar. Included in some of the images is output from NSSL's Mesocyclone Detection Algorithm (MDA) , Tornado Detection Algorithm (TDA), and Bounded Weak Echo Region Algorithm (BWER).  A yellow circle represents a mesocyclone as detected by the MDA.  The red-in-yellow circle represents a mesocyclone whose base is at the lowest radar scan (where it is a more likely tornado threat).  A red triangle indicates the location of a tornado vortex signature as detected by the TDA.


Description:  The reflectivity loop captures some sense of the structure of this storm throughout its lifetime.  Tornadoes were embedded in the center of the storm, behind an arcing band of convection.  The storm appears to be HP.  Select reflectivity cross sections reveal the low-topped nature of the storm.

Initial Structure:

First Tornado, near Murphytown: Second Tornado, near Moundsville: Description:  When the Level II radar data begins recording at (04:07), the storm already has an impressive structure.  The MDA detects mesocyclones both with the central storm, and in the new convection that arcs outward.  A BWER is also observed in the area between the two mesocyclones.

From this point, the MDA proceeds to track an unusually steady state mesocyclone with this storm for 40 minutes, at which time it produces its first tornado.  A time-height trend shows the mesocyclone to strengthen significantly just prior to tornadogenesis.  A closer examination of the reflectivity and velocity data shows shear through the depth of the storm at (04:48).  However, this shallow storm is only sampled on the lowest four tilts, and tilt four views the divergent, upper region of the storm.  The tornado near Murphytown did considerable damage to a few structures outside of town; the damage was rated F2.

One hour, and three severe wind reports later, a second tornado touches down south of Moundsville.  This tornado, although a weak F1, would track 11 miles over 15 minutes.  By this time, the storm is far from the radar location, presenting a challenge to the MDA.  Range folded echos become a problem, and the storm can only be scanned on the lowest three radar tilts;  the mesocyclone on the lowest two radar tilts.  The MDA, though, has been designed to detect lowtop mesocylones, even at long range.  Color coded attributes in the meso table alert the forecaster to the strength of the detection.

Link to the NWSFO in Charleston, WV