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000
ACUS11 KWNS 171839
SWOMCD
SPC MCD 171839
ALZ000-MSZ000-172015-

MESOSCALE DISCUSSION 0667
NWS STORM PREDICTION CENTER NORMAN OK
0139 PM CDT FRI MAY 17 2013

AREAS AFFECTED...MS...AL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 171839Z - 172015Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...TSTMS ARE EXPECTED TO CONTINUE TO TRACK EAST FROM NERN MS
INTO NRN AND CNTRL AL THROUGH THE LATE AFTERNOON AS A WEAK UPPER
LEVEL DISTURBANCE MOVES EAST FROM THE LOWER MS RIVER VALLEY.
ADDITIONAL STORM DEVELOPMENT ALSO SEEMS POSSIBLE FROM CNTRL AND ERN
MS EWD INTO AL AS AIRMASS CONTINUES TO DESTABILIZE WITH HEATING OF
THE DAY. IN ADDITION TO LOW PROBABILITY TORNADO THREAT...A FEW OF
THE STRONGER STORMS MAY PRODUCE HAIL.

DISCUSSION...LIFT ASSOCIATED WITH A WEAKENING SHORTWAVE TROUGH NOW
CROSSING THE LOWER MS VALLEY WILL CONTINUE TO ACT ON A MOIST AND
SLOWLY DESTABILIZING AIRMASS ACROSS MS/AL THIS AFTERNOON. DESPITE
AREAS OF THICKER CLOUD COVER SOUTH OF THE ONGOING WEAKLY ORGANIZED
MCS OVER NERN MS AND NWRN AL...A GRADUAL INCREASE IN CAPE AND
DECREASE IN INHIBITION HAS OCCURRED AS SFC TEMPS HAVE WARMED TO NEAR
80F. LOW LEVEL ASCENT OVER THE REGION MAY INCREASE ALONG A THERMAL
GRADIENT/WARM FRONT BETWEEN THE MCS TO THE NORTH AND BROKEN
CLOUDINESS SOUTH. IN THE NEAR TERM...MESOSCALE ASCENT AND POTENTIAL
STORM INITIATION MAY BE MAXIMIZED ACROSS CNTRL MS TO WCNTRL AL WHERE
LOW LEVEL SWLY FLOW OF 25-30KT INTERSECTS THE WEAK BOUNDARY. A
SMALLER SCALE MID-LEVEL IMPULSE SPREADING EAST FROM NRN LA MAY ALSO
ENHANCE THE POTENTIAL FOR STORM INITIATION THROUGH LATE
AFTERNOON/EARLY EVENING.

A WLY MID-LEVEL SPEED MAX OF ABOUT 50KT ASSOCIATED WITH THE MS
VALLEY SHORTWAVE WILL CONTRIBUTE TO DEEP LAYER VERTICAL SHEAR
SUPPORTIVE OF UPDRAFT ROTATION/PERSISTENCE IN ANY STORMS THAT CAN
DEVELOP. VWP DATA ACROSS THE REGION ALSO DEPICTS MODEST DIRECTIONAL
SHEAR THAT COULD FAVOR LOW LEVEL STORM ROTATION AND A LOW CHANCE OF
A TORNADO. THE COMPACT AND WEAKENING NATURE OF THE MID/UPPER FORCING
DOES SUGGEST THAT OVERALL STORM COVERAGE MAY BE LIMITED WITH THE
BEST CHANCE FOR SEVERE WEATHER OCCURRING FROM LATE THIS AFTERNOON
INTO EARLY EVENING BEFORE DECREASING. A WATCH MAY BE NEEDED WITHIN
THE NEXT 1-2 HOURS IF STORM DEVELOPMENT AND ORGANIZATION BECOME MORE
APPARENT.

..CARBIN/WEISS.. 05/17/2013

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

ATTN...WFO...BMX...HUN...MOB...MEG...JAN...

LAT...LON   33369011 32879031 32479044 32129029 31889010 31838985
            31668957 31588887 31628806 31608742 31778661 32028618
            32278605 32668572 32918563 33368552 33458552 33758559
            33948557 34208580 34428615 34428641 34478670 34548707
            34498739 34318774 33948807 33858841 33718863 33658886
            33498982 33369011