NSSL SWAT Case Study - 18 March 1996 Alabama

This day saw an late winter tornado outbreak in Alabama.  Nearly the entire state experienced thunderstorms, many of them severe.  Several tornadoes occurred when isolated storms developed in front of an advancing squall line.  Outflow from the squall line acted to enhance rotation in the isolated storms.  This is another of the many cases from around the country which NSSL is using to test its Mesocyclone Detection Algorithm (MDA).

Presented here are various WSR-88D radar images from the Birmingham, AL radar (KBMX).  Included in some of the images is output from NSSL's Mesocyclone Detection Algorithm (MDA). A yellow circle depicts a mesocyclone.  A red-in-yellow circle indicates the mesocyclone extends to the lowest elevation scan of the radar (extists near or ar the base of the storm) where it is a more likely tornado threat.

Description:  Around 2245 UTC the KBMX radar went down with a pseudo-MCS entering Alabama.  Supercells were occurring to the south of this feature.  When the radar put out it's next product at 2319 UTC, a number of small cells had gone up simultaneously ahead of the main area of storms. Description:  This circulation was very interesting, a brief but intense spin-up.   Several heavy to severe storms moved across the radar site.  No mesocyclones were evident until the time of the radar frames above.  The circulation existed momentarily to a depth of several thousand feet but had disapated considerably by the time of the next volume scan.  Later, trees were reported down,  and the event was classified as wind damage.  Given the strength of the circulation, however, and its low elevation, there may have been a very short-lived, small tornado. Description:  All significant tornadoes occurred in east central Alabama.  (First Image), the isolated storm at the bottom left was preparing to produce its first F2 tornado which is shown in the (Second Image)(Third Image), a cross section, illustrates the Bounded Weak Echo Region associated with the tornado.

This storm remained a long track cyclic supercell, and, later in its life, it was caught from behind by the advancing squall line (Fourth Image-the cyclic supercell is identified by the number 625).  Outflow from the squall line (Fifth Image) enhanced the latest in a series of tornadoes, and may have contributed to it's producing F3 damage near Jackson's Gap in Tallapoosa County.  Jackson's Gap had also experienced a small F1 tornado less than two hours earlier.

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