NSSL SWAT Case Study - 28 October 1998:

Mini-supercells in Central Oklahoma

The October 28th, 1998, an "outbreak" of mini-supercells occured in Central Oklahoma.  One brief tornado was reported southest of Guthrie Oklahoma.  These storms has radar characteristics of "normal" supercells, but were dwarfed representations.  Presented here are a few radar images of these storms.

The near-storm enviroment of the day was characterized by very large shear values but weak instability.  A proximity sounding at OUN showed a rather low EL (~600mb), owing to very low-topped storms (15-20 Kft).  No cloud-to-ground electrical activity was measured with these storms.

Presented here are various WSR-88D radar images from the Norman, OK (KOUN) radar. Included in some of the images is output from NSSL's Mesocyclone Detection Algorithm (MDA).  A cyan circle represents a 2D vortex feature (from a constant elevation angle) as detected by the MDA.

Description:  The particular mini-supercell SE of Guthrie reportedly produced a brief tornado.  Another mini-supercell is also N of Meridian and may have produced a brief tornado.  Note the weak vortex signatures on the eight-panel display.  Although these signatures have not attained classic "mesocyclone" strength, they are significant relative to the events of this day (since tornadoes were reported), and relative to the strengths of vortices observed on other tornadic mini-supercell storms (see studies by Burgess et al., and Grant and Prentice).  A vertical cross-section through the storm reveals a bounded weak echo region (BWER) and the low top (~20 Kft). Description:  Other mini-supercells also occurred, with this one near Edmond, OK.  This storm prompted a tornado warning from the NWSFO Norman, as its radar characterstics resembled the previously tornadic storm SE of Guthrie.  Note the weak vortices on this storm (and the others nearby), and this storm has a very prominent BWER and low-top.
  Description:  Note, on this vertical cross-section, the "extra" reflectivity patch up to near 37 Kft.  Is this some precipitation from a portion of the storm that "broke through" the 600 mb EL up to the tropopause?

Finally:  Putting these storms in perspective, we borrow the famous "Three Supercells" image of the three tornadic storms with varying horizontal scales.  Here's an image of the Guthrie storm in comparison to the "Three Supercells". Note that the Guthrie storm is of a horizontal scale between the Phoenix storm (the smallest) and the Colorado storm (the middle).


© Greg Stumpf

© Greg Stumpf


Back to NSSL SWAT Case Study Table of Contents Page.