[BNAWX] Severe Storm Outlook Narrative

[EMWIN Server]

ACUS11 KWNS 172044
SWOMCD
SPC MCD 172044
TNZ000-MOZ000-ARZ000-MSZ000-LAZ000-172145-

MESOSCALE DISCUSSION 2065
NWS STORM PREDICTION CENTER NORMAN OK
0344 PM CDT WED OCT 17 2012

AREAS AFFECTED...PARTS OF CENTRAL AND ERN AR/FAR NERN LA/FAR NWRN
MS/FAR WRN TN/MO BOOTHEEL

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 172044Z - 172145Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...SHORT TERM MODEL TRENDS CONTINUE TO SUGGEST TSTMS WILL
DEVELOP ALONG A PRE-FRONTAL TROUGH/DIFFERENTIAL HEATING BOUNDARY
EXTENDING FROM NORTH CENTRAL-NERN AR TO SOUTH CENTRAL AR BETWEEN
22-23Z.  ADDITIONAL STORMS SHOULD ALSO FORM ALONG THE COLD FRONT AS
IT REACHES CENTRAL AR LATE THIS AFTERNOON/EARLY EVENING.  A
MOISTENING BOUNDARY LAYER AND STRENGTHENING...VERTICALLY VEERING
WINDS WILL SUPPORT A TORNADO THREAT...IN ADDITION TO DAMAGING WINDS.

DISCUSSION...18Z SOUNDINGS AT LZK/SHV BOTH INDICATED MOISTENING OF
THE BOUNDARY LAYER BENEATH A CAP BASED AROUND 850 MB WHICH FOR NOW
IS MAINTAINING SURFACE-BASED INHIBITION.  ADDITIONAL MOISTURE RETURN
INTO THE NRN EXTENT OF THE LOWER MS VALLEY COMBINED WITH SURFACE
HEATING...WHICH HAS BEEN STRONGEST ACROSS SRN/ERN AR PER VISIBLE
SATELLITE IMAGERY AND SURFACE OBSERVATIONS...WILL FURTHER
DESTABILIZE THE AIR MASS /MLCAPE APPROACHING 1000 J/KG OVER SRN-SERN
AR LATE THIS AFTERNOON/.  THE 18Z SOUNDINGS ALSO INDICATED 850-700
MB LAYER WINDS HAD BACKED SOME SINCE 12Z AND STRENGTHENED...WITH AN
INCREASE IN WLY MIDLEVEL WINDS ALSO NOTED.  THESE KINEMATICS ARE
SUSTAINING LOW LEVEL HODOGRAPH CURVATURE WITH SURFACE-1 KM SHEAR
AROUND 40 KT FOR A TORNADO THREAT AND EFFECTIVE BULK SHEAR OF 40-50
KT FOR STORM ORGANIZATION.

UNCERTAINTIES REMAIN ABOUT THE DEGREE OF DESTABILIZATION AND AMOUNT
OF FORCING FOR ASCENT ATTENDANT TO A DIGGING NWLY MID-UPPER LEVEL
JET AND TROUGH TO SUPPORT TSTM DEVELOPMENT ACROSS THE DISCUSSION
AREA.  HOWEVER...TRENDS IN SHORT TERM MODELS /HRRR AND 12Z 4 KM
WRF-NMM/NSSL/ CONTINUE TO SUGGEST FACTORS WILL BECOME JUXTAPOSED
ACROSS CENTRAL AR BETWEEN 22-23Z...WITH ADDITIONAL STORM DEVELOPMENT
ALONG THE COLD FRONT BY EARLY EVENING ACROSS CENTRAL AR.

..PETERS/THOMPSON.. 10/17/2012

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

ATTN...WFO...PAH...MEG...JAN...LZK...SGF...SHV...

LAT...LON   34119273 35459216 36509166 36568987 36438943 35398977
            33999057 32979103 32759160 32959248 32999295 34119273



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