DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 271958
SWODY1
SPC AC 271955

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0255 PM CDT SAT APR 27 2013

VALID 272000Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT FROM
SW TX TO PARTS OF AR/TN/MS/AL...

...AR/TN/MS/AL...
PRIMARY CHANGE TO THE PREVIOUS OUTLOOK FOR AR/TN/MS/AL WAS A SMALL
WWD EXTENSION OF THE SLGT RISK AREA INTO CNTRL AR. AFTERNOON SURFACE
OBSERVATIONS AND VISIBLE SATELLITE LOOP SHOW THE PRIMARY SURFACE LOW
MOVING EWD FROM W-CNTRL AR INTO CNTRL AR. CUMULUS FIELD IS BEGINNING
TO SHOW SIGNS OF DEEPENING INVOF THIS FEATURE AS TEMPERATURES OVER
SRN AR CONTINUE TO WARM THROUGH THE 70S. GIVEN MODERATE CAPE AND
SUPERCELL WIND PROFILES...ANY STORMS THAT MATURE OVER CNTRL/SRN AR
WILL BE CAPABLE OF PRODUCING LARGE HAIL...DAMAGING WINDS...AND AN
ISOLATED TORNADO.

OTHERWISE...MAJORITY OF THE PREVIOUS OUTLOOK APPEARS TO BE ON TRACK.
SURFACE LOW PRESSURE IS FORECAST TO ADVANCE ENEWD TOWARD THE LOWER
OH VALLEY BY EVENING...WITH A WARM FRONT CURRENTLY ANALYZED FROM SRN
AR INTO NRN MS AND NWRN AL LIFTING NWD INTO WRN/MIDDLE TN...WHILE A
COLD FRONT MOVES EWD INTO THE LOWER MS VALLEY. CONVECTION HAS BEEN
SLOW TO MATURE INTO THUNDERSTORMS THUS FAR DUE IN PART TO CLOUDINESS
ACROSS THE WARM SECTOR. HOWEVER...SHORT-TERM MODEL GUIDANCE
INDICATES DESTABILIZATION WILL CONTINUE...LEADING TO SCATTERED
THUNDERSTORM COVERAGE BY LATE AFTERNOON/EVENING. BUOYANCY AND SHEAR
WILL BE FAVORABLE FOR ORGANIZED THUNDERSTORM DEVELOPMENT...INCLUDING
SUPERCELLS...WHICH WILL POSE A RISK FOR LARGE HAIL...DAMAGING
WINDS...AND A COUPLE OF TORNADOES. DUE TO THE SLOW EVOLUTION OF
THUNDERSTORM DEVELOPMENT THIS AFTERNOON...CONFIDENCE HAS DECREASED
IN THE OCCURRENCE OF A CONCENTRATED SWATH OF LARGE HAIL OVER SWRN
TN/NRN MS. THEREFORE...THE 30 PERCENT HAIL PROBABILITY HAS BEEN
ELIMINATED.

...LA INTO E-CNTRL/SERN TX...
STRONG DESTABILIZATION IS OCCURRING ACROSS E-CNTRL/SERN TX...WITH A
CLUSTER OF STORMS RECENTLY DEVELOPING W OF HOU. COVERAGE IS EXPECTED
TO INCREASE THIS AFTERNOON ACROSS THE AREA...AND WILL POSE A LARGE
HAIL/DAMAGING WIND THREAT GIVEN THE MOIST AND UNSTABLE ENVIRONMENT
THAT IS CURRENTLY OBSERVED.

...S-CNTRL TX...
A SURFACE FRONTAL BOUNDARY REMAINS QUASI-STATIONARY FROM ROUGHLY 20
N OF AUS WWD ACROSS THE EDWARDS PLATEAU. SKIES HAVE PARTIALLY
CLEARED ALONG THIS BOUNDARY...WHICH IS AIDING IN TEMPERATURES
WARMING INTO THE 80S. AS A RESULT...CONVECTIVE INHIBITION IS SLOWLY
WEAKENING. ALONG AND S OF THE FRONT...SURFACE DEWPOINTS ARE IN THE
LOW TO MID 60S. THIS MOISTURE COMBINED WITH STEEP MIDLEVEL LAPSE
RATES IS CONTRIBUTING TO MLCAPE VALUES IN EXCESS OF 2000 J/KG. THE
17Z HRRR CONTINUES TO SHOW A CLUSTER OF STORMS FORMING ALONG THE
FRONT BY LATE AFTERNOON. GIVEN THE STRONG INSTABILITY COUPLED WITH
LOW-LEVEL ELYS OCCURRING BENEATH 30+ KT MIDLEVEL WLYS...ENVIRONMENT
WILL BE SUPPORTIVE OF SPLITTING SUPERCELLS CAPABLE OF PRODUCING VERY
LARGE HAIL.

FARTHER S...STRATUS HAS BEEN SLOW TO ERODE INVOF THE RIO
GRANDE...WHICH IS DELAYING ROBUST BOUNDARY LAYER DESTABILIZATION.
THIS YIELDS UNCERTAINTY IN WHETHER STORMS THAT MAY INITIATE OVER THE
HIGHER TERRAIN IN MEXICO WILL BE ABLE TO PERSIST EWD INTO S TX.
THUS...THREAT FOR LARGE HAIL/DAMAGING WINDS IS MORE CONDITIONAL
COMPARED TO LOCATIONS CLOSER TO THE FRONT.

..GARNER.. 04/27/2013

.PREV DISCUSSION... /ISSUED 1110 AM CDT SAT APR 27 2013/

...AR/TN/MS...
MORNING SATELLITE IMAGERY SHOWS A COMPACT UPPER LOW OVER WESTERN
MO...AND A SHORTWAVE TROUGH EXTENDING SOUTHWARD FROM THE LOW INTO
WESTERN AR. THE TROUGH WILL ROTATE EASTWARD TODAY INTO THE MID MS
VALLEY AND PROVIDE LARGE SCALE ASCENT FOR THE DEVELOPMENT OF
SCATTERED SHOWERS AND THUNDERSTORMS. SURFACE ANALYSIS INDICATES A
LOW OVER SOUTHEAST OK AND A WARM FRONT EXTENDING EASTWARD ACROSS
CENTRAL AR INTO SOUTHWEST TN. INCREASING BREAKS IN THE CLOUDS TO
THE SOUTH OF THE WARM FRONT WILL HELP TO SLOWLY DESTABILIZE THE AIR
MASS...WHILE DEWPOINTS CLIMB INTO THE MID 60S. THIS SCENARIO SHOULD
RESULT IN A FOCUSED AREA OF STRONG/SEVERE THUNDERSTORM DEVELOPMENT
LATER THIS AFTERNOON AND EVENING ACROSS PARTS OF EASTERN AR/WEST
TN/NORTHERN MS. FORECAST SOUNDINGS SHOW STRONG EFFECTIVE SHEAR AND
0-3KM HELICITY VALUES OF 150-250 M2/S2. THESE PARAMETERS COUPLED
WITH SUFFICIENT INSTABILITY WILL PROMOTE THE RISK OF SUPERCELLS
CAPABLE OF LARGE HAIL...DAMAGING WINDS...AND ISOLATED TORNADOES.
ACTIVITY WILL SPREAD EASTWARD THROUGH THE EVENING INTO MIDDLE TN AND
NORTHWEST AL BEFORE WEAKENING.

...LA/EAST TX...
A COLD FRONT CURRENTLY EXTENDS FROM THE AFOREMENTIONED LOW OVER
SOUTHEAST OK INTO EAST TX. THIS BOUNDARY IS EXPECTED TO SAG
SOUTHEASTWARD INTO NORTHWEST LA BY LATE AFTERNOON. MODEL SOLUTIONS
ARE IN AGREEMENT THAT THE CAPPING INVERSION SHOULD WEAKEN THROUGH
THE DAY LEADING TO SCATTERED THUNDERSTORMS ALONG THE FRONT. LOW
LEVEL SHEAR IS EXPECTED TO BE RATHER WEAK...BUT SUFFICIENT DEEP
LAYER FLOW AND MODERATE INSTABILITY WILL PROMOTE STRONG UPDRAFTS
CAPABLE OF HAIL AND GUSTY WINDS.

...SOUTH CENTRAL TX...
THE COLD FRONT IS FORECAST TO EXTEND FROM AUS WESTWARD ACROSS THE
HILL COUNTRY LATER THIS AFTERNOON. MORNING STRATUS TO THE SOUTH OF
THE FRONT IS SLOWLY BURNING OFF...WHICH SHOULD HELP TO YIELD
AFTERNOON MLCAPE VALUES OF 2500 J/KG. DEEP WEAK EASTERLY LOW LEVEL
FLOW BENEATH MODERATELY STRONG WESTERLY FLOW AT MID LEVELS WILL
PROVIDE SUFFICIENT SHEAR FOR ORGANIZED/SUPERCELL STORMS CAPABLE OF
LARGE HAIL AND DAMAGING WINDS.

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