DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 241953
SWODY1
SPC AC 241951

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0251 PM CDT TUE SEP 24 2013

VALID 242000Z - 251200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM SERN MS INTO SWRN AL...

...SERN MS THROUGH SRN AL...

PRIMARY CHANGE TO ONGOING FORECAST HAS BEEN TO INTRODUCE A SMALL
SLIGHT RISK FROM SERN MS INTO SWRN AL TO ACCOUNT FOR ONGOING STRONG
TO SEVERE STORMS.

A QUASI-STATIONARY FRONT EXTENDS FROM NRN FL WNWWD THROUGH SWRN AL
AND SERN MS WHERE IT INTERSECTS A PROGRESSIVE CONVECTIVE OUTFLOW
BOUNDARY. THUNDERSTORMS /SOME STRONG TO POTENTIALLY SEVERE/ REMAIN
ACTIVE ALONG THIS BOUNDARY. DIABATIC WARMING OF THE MOIST SFC LAYER
WITH LOW 70S DEWPOINTS HAS CONTRIBUTED TO 1000-1500 J/KG MLCAPE IN
THE WARM SECTOR. STORMS WILL LIKELY CONTINUE DEVELOPING ALONG THE
CONVECTIVE OUTFLOW BOUNDARY...ALONG A PRE-FRONTAL CONVERGENCE AXIS
IN SERN MS AS WELL AS WITHIN ZONE OF LOW LEVEL WARM ADVECTION ALONG
AND NORTH OF THE WARM FRONT ACROSS SERN MS AND SWRN AL INTO EARLY
EVENING. WHILE DEEP LAYER WINDS ARE NOT PARTICULARLY STRONG...A BELT
OF MODEST 700-500 MB SWLY FLOW WITHIN BASE OF NEGATIVE TILT TROUGH
ABOVE LIGHT SELY WINDS IS RESULTING IN 30-35 KT EFFECTIVE SHEAR.
SOME STORMS WITHIN THE LINE CONTINUE TO EXHIBIT ORGANIZATION
INCLUDING COMMA HEAD AND BOWING STRUCTURES. POTENTIAL ALSO EXISTS
FOR A FEW STORMS TO DEVELOP MARGINAL SUPERCELL CHARACTERISTICS.
PRIMARY THREAT APPEARS TO BE ISOLATED DAMAGING WIND...BUT A BRIEF
TORNADO CANNOT BE RULED OUT.

..DIAL.. 09/24/2013

.PREV DISCUSSION... /ISSUED 1111 AM CDT TUE SEP 24 2013/

...SYNOPSIS...
WRN IA-MO UPR TROUGH EXPECTED TO CONTINUE SHEARING ESE THIS PERIOD
AS EMBEDDED VORTICITY CENTERS ON ITS SRN SIDE CONTINUE ESE INTO THE
LWR OH AND TN VLYS. OTHERWISE...A BROADER...LARGER-SCALE TROUGH NOW
OVER THE NE PACIFIC WILL AMPLIFY SE INTO THE PACIFIC NW...WITH A
LARGE CLOSED LOW EXPECTED TO BE CENTERED OVER THE ORE-WA BORDER BY
12Z WED.

AT THE SFC...SHALLOW...RESIDUAL LAYER OF POLAR AIR ASSOCIATED WITH
CANADIAN MARITIMES UPR LOW EXPECTED TO CONTINUE MODIFYING OVER THE
LWR MS VLY/GULF CST STATES. THE SRN FRINGE OF THIS AIR MASS IS
MARKED BY WEAK WARM FRONT THAT ATTM EXTENDS FROM SW MS ESE INTO THE
NERN GULF/N FL. THE BOUNDARY SHOULD EDGE SLIGHTLY NWD TODAY IN
RESPONSE TO DAYTIME HEATING AND GRADUAL WEAKENING OF ERN U.S. SFC
RIDGE.

UPLIFT ALONG THE WARM FRONT...AND ASCENT ASSOCIATED WITH
DISTURBANCES ON SRN FRINGE OF IA-MO LOW...WILL SUPPORT EPISODES OF
STRONG TO POTENTIALLY SVR TSTMS OVER PARTS OF THE LWR MS VLY/CNTRL
GULF CST STATES...AND PERHAPS FL...LATER TODAY.

...LWR MS VLY/CNTRL GULF CST THIS AFTN/EVE...
SW-NE BAND OF TSTMS NOW OVER LA-MS IS ASSOCIATED WITH A PROGRESSIVE
BAND OF DEEP CONFLUENCE ARCING S/SW FROM IA-MO UPR LOW. UPLIFT ALONG
THIS AXIS SHOULD CONTINUE TO SUPPORT STORM DEVELOPMENT AS IT
ADVANCES GENERALLY E/SEWD THROUGH THE REMAINDER OF THE DAY.

MID-LVL LAPSE RATES ACROSS THE REGION WILL REMAIN WEAK...AND WLY
DEEP SHEAR FAIRLY MODEST /25-30 KTS/. BUT WIND PROFILES WILL BE
SUFFICIENT FOR SOME DEGREE OF STORM ORGANIZATION AND
SUSTENANCE...ESPECIALLY GIVEN LINEAR LOW-LVL FORCING. COUPLED WITH
FILTERED SFC HEATING AND RICH MOISTURE AVAILABILITY /PW AOA 2
INCHES/...SETUP COULD YIELD EMBEDDED LOW-AMPLITUDE LEWPS/BOWS
CAPABLE OF LOCALLY DMGG WIND /REF MCD 1909/. A LIMITED THREAT ALSO
WILL EXIST FOR A BRIEF TORNADO OR TWO GIVEN WEAK BUT BACKED LOW-LVL
FLOW AHEAD OF CONFLUENCE BAND. A BRIEF TORNADO ALSO COULD OCCUR WITH
ANY STRONGER/MORE SUSTAINED UPDRAFTS FORMING INVOF DIFFUSE WARM
FRONT OVER SRN MS AND WRN AL LATER TODAY.

...FL THIS AFTN...
ERN EXTENT OF LWR MS VLY/NERN GULF WARM FRONT WILL ALSO SERVE AS A
FOCUS FOR DIURNALLY-ENHANCED STORMS OVER THE FL PENINSULA.
CONVERGENCE ACROSS THE REGION WILL...HOWEVER...ALSO BE MODULATED BY
OUTFLOW BOUNDARIES/DIFFERENTIAL HEATING ASSOCIATED WITH DISTURBED
CONVECTIVE AREA NOW CENTERED SW OF TAMPA.

GIVEN HIGH PW OVER CNTRL AND SRN PARTS OF THE PENINSULA /UP TO 2.50
INCHES/ AND 20-25 KT MEAN LOW-MID TROPOSPHERIC WSW FLOW...SETUP
COULD YIELD A STORM OR TWO CAPABLE OF LOCALLY DMGG SFC WIND THROUGH
LATE IN THE DAY.

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