Wednesday, January 30, 2013

Observed environment of killer tornado in Adairsville GA

On January 30, a discrete cell moved northeastward from central AL to nwrn GA... by which time a long-lived QLCS began to "absorb it" from behind.  Storm motion was 50-55 kt during this period as it gradually curved from direction ~210° to ~225°.  Just about the time it was becoming absorbed by the QLCS (~1615Z) the cell spawned a rather substantial-looking tornado in and around the city of Adairsville GA.  This tornado killed at least one person and overturned numerous vehicles per the LSR.  WFO Peachtree City, 55nm to the SSE of the tornadic storm, launched a special RAOB about 45 minutes us a somewhat rare look at the observed environment of a tornado.  A link to a short video clip of the tornado is here:

I modified the RAOB very slightly via cooling the near-surface layer a bit to be perhaps more representative of the inflow; while the surface wind on the RAOB looked sufficiently representative.  Am not getting terribly cute regardless given some showers existed in the inflow environment.

Here are some of the parameters from the modified RAOB.  Should note first, the often typical "weaker SRH" (due usually to a more veered sfc-kink shear vector and/or a weaker LLJ) NAM solution actually was more correct by comparison than the RAP solution was.  Usually the RAP is the winner in this department.  Also, the 2-6 km anticyclonic kink/subtle veer-back-veer pattern with height--and associated SR-flow weakness--fcst by both the NAM and the RAP...which I've found present in a good handful of observed tornadic supercell environments...was not present whatsoever via the RAOB.  i.e., the cell likely had favorable SR flow at all levels.  The angle between the surface to kink shear vector and the storm motion is less than 60 degrees... not atypical of many tornadoes in the ern United States--in fact the hodograph itself is quite reminiscent of some past sig tor events' observed hodographs in MS/AL/TN.  And finally, the RAOB hodograph's "Bunkers right mover" fcst motion for this cell during its tornadic phase nailed the observed motion, with the direction essentially spot on and the speed very close or a touch faster than observed (not surprising given the somewhat shallow convective layer?).  The storm was certainly an EL-buster based on the echo tops/visible satellite presentation.

Sfc T/Td: 68/64°F
SBCAPE: 440 J/kg
SBCIN: 12 J/kg

ML T/Td: 71/63°F
MLCAPE: 428 J/kg
MLCIN: 1 J/kg

0-3 km MLCAPE: 139 J/kg
MLLCL: 566 m
MLLFC: 669 m

0-1 km SRH: 344 m2/s2
0-3 km SRH: 495 m2/s2
0-6 km bulk shear: 75 kt
storm motion: 228° @ 53 kt