DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 122000
SWODY1
SPC AC 121958

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0158 PM CST TUE FEB 12 2013

VALID 122000Z - 131200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL/ERN GULF COAST
STATES THIS AFTN AND TONIGHT...

--- UPDATES ---

...GULF COAST SVR OUTLOOK...
CATEGORICAL RISK HAS BEEN EXPANDED SOMEWHAT OVER SRN LA IN DEFERENCE
TO CONVECTIVE TRENDS NEAR SFC LOW AND FAVORABLE SLIVER OF
WARM-SECTOR AIR THAT WILL PRECEDE THIS CONVECTION. REF SPC
MESOSCALE DISCUSSION 157 FOR NEAR-TERM FCST DETAILS. OTHERWISE WILL
CONTINUE POTENTIAL FOR DAMAGING WIND AND A FEW TORNADOES ALONG AND S
OF WARM FRONT. LARGEST HODOGRAPHS WILL REMAIN INVOF FRONT WHERE SFC
FLOW IS MOST STRONGLY BACKED...OFFERING SOMEWHAT ENHANCED RISK WHERE
SUPERCELLS ORIGINATING IN WARM SECTOR CAN CROSS RELATED FIELD OF
RELATIVELY MAXIMIZED LOW-LEVEL VORTICITY/SRH. FAVORABLE LOW-LEVEL
SHEAR IS EXPECTED OVER COASTAL WARM SECTOR AS WELL.

SPORADIC/MRGL SVR HAIL AND ISOLATED GUSTS NEAR SVR LIMITS REMAIN
POSSIBLE WITH ELEVATED SUPERCELLS N OF WARM FRONT...PROBABILITIES
FOR EACH DIMINISHING WITH NWD EXTENT INTO REGIME OF PROGRESSIVELY
WEAKER AND MORE ELEVATED BUOYANCY. SFC MESOANALYSIS SHOWS SFC WARM
FRONT HAS MOVED INLAND S-CENTRAL/SERN LA...AND EXTENDS EWD ACROSS
CHANDELEUR ISLANDS AREA TO JUST OFFSHORE MOB/PNS...INLAND AGAIN
BETWEEN TLH-AAF. FRONT SHOULD CONTINUE MOVING SLOWLY NWD THROUGH
REMAINDER PERIOD AHEAD OF WAVE LOW ANALYZED AT 19Z OVER BPT
AREA...AS LOW SHIFTS ENEWD OVER MS/AL/GA.

...TX/OK GEN TSTMS...
TSTM AREA HAS BEEN UPDATED TO REFLECT CONVECTIVE TRENDS SINCE PRIOR
OUTLOOK...INCLUDING MID-UPPER DRY SLOT EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER N-CENTRAL/NE TX AND SRN OK. VERY TRANSIENT LTG
PRODUCTION CANNOT BE RULED OUT FROM SHALLOW/LOW-TOPPED/COLD-CORE
CONVECTION OVER W-CENTRAL TX. HOWEVER...FCST SOUNDINGS SUGGEST
MUCAPE BELOW 100 J/KG ROOTED AROUND 700 MB AND CAPPED BY MID-UPPER
LEVEL STABLE LAYER THAT WILL SUBSIDE BELOW ELEVATION OF -20 DEG C
ISOTHERM WITH TIME. GIVEN THIS FACTOR...TSTM POTENTIAL APPEARS TOO
ISOLATED/BRIEF FOR GEN THUNDER LINE.

..EDWARDS.. 02/12/2013

.PREV DISCUSSION... /ISSUED 1018 AM CST TUE FEB 12 2013/

...SYNOPSIS...

THE PRIMARY FEATURE OF INTEREST THROUGH WEDNESDAY MORNING WILL BE A
POSITIVELY TILTED...SRN BRANCH SHORT-WAVE TROUGH WHICH WILL
TRANSLATE FROM THE SRN HIGH PLAINS INTO THE MID SOUTH AND OZARK
PLATEAU. A BELT OF STRONG...MID AND UPPER-TROPOSPHERIC FLOW WILL BE
MAINTAINED ON THE EQUATORWARD SIDE AND DOWNSTREAM OF THIS
SYSTEM...GENERALLY FROM THE SRN PLAINS TO ATLANTIC SEABOARD. WITHIN
THIS HIGH MOMENTUM AIR STREAM...MORNING WATER VAPOR IMAGERY SUGGESTS
THE PRESENCE OF A WEAK VORTICITY MAXIMUM OVER ERN TX WHICH WILL MOVE
RAPIDLY ACROSS THE GULF COAST STATES TODAY.

AT THE SURFACE...15Z ANALYSIS SHOWED AN AREA OF LOW PRESSURE ALONG
THE TX COAST /NEAR LBX/ WITH AN ASSOCIATED STATIONARY FRONT
EXTENDING ENEWD ALONG THE SRN LA COAST AND ACROSS NRN FL. THIS
SURFACE LOW IS FORECAST TO DEEPEN TODAY WHILE DEVELOPING ENEWD ALONG
THE BAROCLINIC ZONE INTO FAR SWRN MS BY 13/00Z AND EVENTUALLY INTO
NERN AL BY THE END OF THE D1 PERIOD. THE PRECEDING SURFACE FRONT
WILL ACCORDINGLY LIFT NWD...LIKELY EXTENDING FROM THE CYCLONE ESEWD
THROUGH CNTRL GA AND SRN SC BY 13/12Z.

...CNTRL/ERN GULF COAST STATES TODAY AND TONIGHT...

A CONSIDERABLE BROADENING AND INTENSIFICATION OF A SWLY LLJ WILL
OCCUR IN RESPONSE TO THE EWD ADVANCEMENT OF THE PRIMARY UPPER-AIR
SYSTEM THROUGH THE SRN PLAINS. THIS WILL ENHANCE THE NWD FLUX OF AN
EXCEEDINGLY MOIST AIR MASS INLAND IN THE WAKE OF WARM FRONTAL
PASSAGE WITH DEWPOINTS RISING THROUGH THE 60S WITHIN THE EXPANDING
WARM SECTOR. HOWEVER...LAPSE RATES WILL REMAIN RELATIVELY
POOR...LIMITING MLCAPE VALUES TO GENERALLY LESS THAN 1000 J/KG.

A BAND OF ELEVATED TSTMS IS IN PROGRESS AS OF MID MORNING FROM
E-CNTRL TX EWD INTO CNTRL AL WITHIN 925-850-MB FRONTAL ZONE WHERE
WAA/ISENTROPIC ASCENT IS BEING ENHANCED BY THE STRENGTHENING LLJ.
THESE PROCESSES WILL LIKELY MAINTAIN A SIMILAR REGIME ACROSS INLAND
PORTIONS OF THE GULF STATES TODAY...ESPECIALLY AS DEEP-LAYER ASCENT
IS AIDED BY THE EWD PROGRESSION OF THE LEAD VORTICITY MAXIMUM
MENTIONED IN THE SYNOPSIS. SOME MARGINALLY SEVERE HAIL WILL BE
POSSIBLE WITH THE STRONGEST STORMS GIVEN STRONG CLOUD-BEARING SHEAR
AND THE PRESENCE OF MODEST...ELEVATED INSTABILITY /SEE THE 12Z LCH
SOUNDING/.

SURFACE-BASED TSTM DEVELOPMENT WILL BECOME INCREASINGLY LIKELY THIS
AFTERNOON FROM THE VICINITY OF THE SURFACE LOW EWD ALONG THE WARM
FRONT WITH THIS POTENTIAL SPREADING INLAND THROUGH SRN PARTS OF
AL/GA DURING THE LATTER HALF OF THE FORECAST PERIOD. MODEL-DERIVED
HODOGRAPHS WITHIN EXPANDING WARM SECTOR SHOW 50-60 KT OF DEEP-LAYER
SHEAR WITH EFFECTIVE SRH VALUES INCREASING TO 250-350 M2/S2. AS
SUCH...THE POTENTIAL WILL EXIST FOR EMBEDDED SUPERCELL AND BOWING
STRUCTURES CAPABLE OF TORNADOES AND DAMAGING WINDS.

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