[BNAWX] Severe Storm Outlook Narrative

[EMWIN Server]

ACUS11 KWNS 201008
SWOMCD
SPC MCD 201008
ALZ000-TNZ000-MSZ000-LAZ000-ARZ000-201115-

MESOSCALE DISCUSSION 2186
NWS STORM PREDICTION CENTER NORMAN OK
0408 AM CST THU DEC 20 2012

AREAS AFFECTED...ERN AR/WRN TN/LA/MS/WRN AL

CONCERNING...SEVERE THUNDERSTORM WATCH 688...

VALID 201008Z - 201115Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 688
CONTINUES.

SUMMARY...A THREAT FOR DAMAGING WINDS AND A TORNADO OR TWO PERSISTS
ACROSS WW 688...WITH RECENT TRENDS IN STORM INTENSITY/LIGHTNING DATA
SUGGESTING THESE THREATS TO BE GREATEST ACROSS AR/TN/NWRN MS
PORTIONS OF THIS SVR TSTM WATCH.

MEANWHILE...NEW CONVECTION/TSTMS WILL CONTINUE TO DEVELOP OVER SERN
LA AND SRN MS...WITH THIS ACTIVITY TRACKING ENEWD INTO CENTRAL/SRN
AL.  THIS WARM SECTOR ACTIVITY MAY WARRANT A SEPARATE WW.

DISCUSSION...TRENDS IN REGIONAL RADAR IMAGERY/LIGHTNING DATA SHOWED
SUSTAINED TSTMS/QLCS PROGRESSING EWD INTO NWRN MS...AND APPROACHING
FAR WRN TN.  DESPITE WEAKER INSTABILITY IN THESE AREAS /MUCAPE
200-400 J PER KG/...STRONGER FORCING FOR ASCENT/DPVA ATTENDANT TO
THE STRONG SHORTWAVE TROUGH MOVING TOWARD THE MID MS/LOWER OH/TN
VALLEYS WILL MAINTAIN QLCS WITH EWD EXTENT.  WFO/S MAY NEED TO
EXTEND THE NRN PART OF WW 688 EWD TO INCLUDE MORE OF SWRN TN AND NRN
MS EARLY THIS MORNING.

THE SRN EXTENT OF THE QLCS HAS BECOME LESS INTENSE /I.E. LACK OF CG
LIGHTNING/ ACROSS NERN TO SWRN LA. THIS IS LIKELY DUE TO A MIDLEVEL
WARM LAYER NOTED ON THE 06Z SLIDELL SPECIAL SOUNDING. ALTHOUGH THIS
LINE HAS WEAKENED...GREATER CONCERN EXISTS IN THE PRE-FRONTAL WARM
SECTOR ACROSS SERN LA TO SRN MS WHERE RICH MOISTURE EXISTS WITH
SURFACE DEWPOINTS AROUND 70 F.  RADAR IMAGERY SHOWED SOME LOW LEVEL
ROTATION WITH THE CONVECTION/TSTMS TO THE SSW-NNE OF KBTR.  THUS...A
TORNADO THREAT MAY BE DEVELOPING WITH THIS PRE-FRONTAL ACTIVITY AS
IT PROGRESSES ENEWD ACROSS SRN MS TO CENTRAL/SRN PARTS OF AL THIS
MORNING.  VWP DATA AT SLIDELL HAS SHOWED 40-45 KT 850 MB FLOW BEING
MAINTAINED WITH LOW LEVEL SPEED SHEAR AND HODOGRAPH CURVATURE /0-1
KM SRH AROUND 200 M2 PER S2/.

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

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

ATTN...WFO...OHX...BMX...HUN...MOB...MEG...JAN...LIX...LZK...
LCH...SHV...

LAT...LON   30899297 32469200 33499115 34859055 35469039 35438881
            34958751 32998767 31438793 30658887 30369048 30209152
            30899297


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