NSSL SWAT Case Study - 13 June 98 Oklahoma City Dryline Supercell Tornadoes


 
This page provides a preliminary look at the Oklahoma City (KTLX) WSR-88D radar data from Saturday, the13th of June, 1998.  Oklahoma City experienced its first significant tornado since 1992.  The supercell thunderstorm responsible produced occassional tornadoes, some damaging, as it moved from western Canadian county across Oklahoma couny and into Lincoln county where it weakened.  The most destructive tornado struck north Oklahoma City near Interstates 35 and 44, and has been given a preliminary ranking of F2 on the Fujita tornado damage scale.

Presented here are various WSR-88D radar images from the Oklahoma City (KTLX) WSR-88D radar. Included in some of the images is output from NSSL's Mesocyclone Detection Algorithm (MDA) and Tornado Detection Algorithm (TDA).  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 as detected by the TDA.

Description:   The Guthrie storm began its tornado development around 2308 UTC when an RFD began to descend to the ground from the back side of the storm updraft.  The KTLX base storm relative velocity image at 2308 UTC showed near uniform inflow into the storm with no evidence of rotation.  The reflectivity pattern, however revealed a small hook shape associated with a mid-level mesocyclone (2308 UTC).   Further evidence of a mid-level meso existed at radar Sweep 4.

The RFD made its first significant appearance at the base scan at 2320 UTC.  The RFD was clearly evident by 2332 UTC.  A tornado developed at the north side of the RFD; it then occluded and moved north.  The Six Panel image illustrates the tornado formation sequence.  The RFD gust front is evidenced by the green pixels which denote winds inbound toward the radar.  The tornadic circulation is denoted by side by side inbound and outbound velocities which are located at the north end of the RFD gust front.  The Four Panel image follows the parent thunderstorm as it dissipates.  The storm had been moving east, making use of the strong directional shear in the environment.  The four panel image clearly shows how the storm began to lift northward and weaken as a result.
 

Description:  Just as the Guthrie storm was dying off, a new supercell was growing in strength in western Canadian county.  At 2350 UTC the storm had an impressive reflectivity structure.  A tornado warning was issued at 2356 UTC as the mid-level meso strengthened.  No circulation was evident at base scan, but there was greater than 30 knot inflow into the storm (bright pink areas - bottom left), and the Sweep 2 images show a strong circulation/hook echo aloft (right).  The hook echo and circulation developed to base scan level by 0003 UTC.

A tornado subsequently formed northwest of El Reno.  The exact time and location of this tornado are still being investigated.  The Six Panel Tornado Sequence follows the storm through the time when the tornado most likely occurred.
 

Description:  Following the El Reno tornado, this supercell thunderstorm went through a period of Reorganization upon approaching northwest Oklahoma City.  Between 0048 UTC and 0054 UTC a vivid hook echo materialized and base scan circulation increased dramatically.  At 0103 UTC a water spout formed on Lake Heffner and quickly moved onshore doing significant damage.

The 0106 UTC and 0112 UTC storm relative velocity images were truly scary, showing an intense mesocyclone just above the ground in a densely populated area.  The 0124 UTC reflectivity image is equally as scary; when a "blob" of reflectivity is observed at the end of a "fish-hook," a tornado is almost a guarantee.  As it turned out, the meso dropped occasional tornadoes across north Oklahoma City with the most intense damage being F2.  There were no fatalities and no serious injuries.  The storm's circulation broke apart as it left Oklahoma City (0130 UTC - 0142 UTC).    


Here's Jim Ladue's page on the 13 June 1998 OKC storm.

 

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