MESO: Mesoscale Discussion 2184

ACUS11 KWNS 200650
SWOMCD
SPC MCD 200650
TNZ000-MSZ000-ARZ000-LAZ000-200745-

MESOSCALE DISCUSSION 2184
NWS STORM PREDICTION CENTER NORMAN OK
1250 AM CST THU DEC 20 2012

AREAS AFFECTED...ERN AR...NRN LA...WRN MS AND WRN TN

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 200650Z - 200745Z

PROBABILITY OF WATCH ISSUANCE...95 PERCENT

SUMMARY...A NEW WW WILL BE COORDINATED AND ISSUED SOON TO THE EAST
OF WW/S 686 AND 687...WITH THE NEW WW LIKELY INCLUDING ERN AR...NRN
LA...WRN MS AND PERHAPS PARTS OF WRN TN. DAMAGING WINDS WILL BE THE
PRIMARY THREAT...THOUGH A TORNADO OR TWO CANNOT BE RULED OUT.

DISCUSSION...LATEST TRENDS IN SURFACE OBSERVATIONS AND OBJECTIVE
ANALYSES INDICATED THE PRE-SQUALL LINE/COLD FRONT AIR MASS ACROSS
ERN AR INTO FAR WRN TN AND SWD IS SLOWLY MODIFYING WITH SURFACE
DEWPOINTS INTO THE LOWER 50 AROUND KMEM. MODIFIED 06Z LIT SPECIAL
SOUNDING SUGGESTED SURFACE DEWPOINTS OF 59-60 F ARE NEEDED FOR
PARCELS TO BE SURFACE-BASED. PREDOMINANT DEEP LAYER SHEAR VECTORS
ORIENTED PARALLEL TO THE EWD MOVING SQUALL LINE AND STRONG FORCING
FOR ASCENT WITH THE CENTRAL PLAINS STORM SYSTEM WILL TEND TO
MAINTAIN A LINEAR STORM MODE WITH DAMAGING WINDS THE PRIMARY THREAT.
HOWEVER...LARGE HODOGRAPH CURVATURE NOTED ON THE 06Z LIT SOUNDING
ALSO SUGGESTS A TORNADO THREAT CANNOT BE RULED OUT...ESPECIALLY WITH
ANY EMBEDDED MESOVORTICES IN THE LINE.

STORM MOTIONS OVER NERN TX/FAR NWRN LA ARE AT 40-45 KT WHILE FARTHER
N INTO NRN AR MOTIONS ARE AT 35-40 KT. DESPITE THE DIFFERENT
SPEEDS...THE SSW-NNE ORIENTATION OF THE LINE WILL RESULT IN MUCH OF
THE MS RIVER REGION BEING AFFECTED BY THESE STORMS AROUND 10Z.

..PETERS/EDWARDS.. 12/20/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MEG...JAN...LZK...SHV...

LAT...LON 31919369 34209257 36459123 35949037 35908891 33418973
32039056 31729113 31729223 31919369

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