SWODY1
SPC AC 312000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT TUE MAR 31 2009
VALID 312000Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE GULF COASTAL REGION
THROUGH NRN FL...
...GULF COAST AREA THROUGH NRN FL AND SRN GA...
A COLD FRONT EXTENDS FROM OCCLUDED LOW OVER THE UPPER MS VALLEY SWD
THROUGH CNTRL IL AND INTO SW LA. A COASTAL FRONT STRETCHES FROM NRN
FL WWD ALONG THE GULF COASTAL AREA WHERE IT INTERSECTS THE COLD
FRONT IN SRN LA. NWD PROGRESSION OF THE COASTAL FRONT HAS BEEN
IMPEDED TO SOME DEGREE BY THE DEVELOPMENT OF WIDESPREAD CONVECTION
WITHIN WARM ADVECTION REGIME NORTH OF THIS BOUNDARY. MOST OF THESE
STORMS REMAIN SLIGHTLY ELEVATED. HOWEVER...STORMS DEVELOPING NEAR
THE COASTAL/WARM FRONT OVER THE WRN FL PANHANDLE ARE BASED NEAR THE
SURFACE WHERE SOME HP SUPERCELL STRUCTURES CONTINUE TO BE OBSERVED.
VWP DATA IN THIS REGION STILL SHOW LARGE LOW LEVEL HODOGRAPHS AND
BULK SHEAR IN EXCESS OF 40 KT. THIS ACTIVITY WILL CONTINUE TO POSE A
RISK OF DAMAGING WIND...LARGE HAIL AND ISOLATED TORNADOES NEXT FEW
HOURS. OTHER STORMS DEVELOPING ALONG A BOUNDARY OVER THE NRN GULF
WILL LIKELY MOVE ONSHORE DURING THE EVENING.
THE LOW LEVEL JET IS FORECAST TO GRADUALLY SHIFT NEWD AWAY FROM THE
WARM SECTOR. HOWEVER...INFLOW FROM THE MOIST WARM SECTOR WILL REMAIN
SUFFICIENT TO SUSTAIN STORMS TONIGHT. INSTABILITY WILL LIKELY BECOME
INCREASINGLY MARGINAL AS STORMS EXPAND ENEWD WITH TIME...BUT
VERTICAL SHEAR WILL REMAIN SUFFICIENT FOR A THREAT OF ISOLATED
DAMAGING WIND AND PERHAPS A TORNADO OR TWO.
...NRN MS...WRN TN THROUGH SRN IL...
A LINE OF FORCED LOW TOPPED CONVECTION HAS DEVELOPED FROM WRN TN
THROUGH SRN IL WHERE THE ATMOSPHERE HAS HEATED IN A NARROW ZONE
AHEAD OF DPVA ASSOCIATED WITH EJECTING SHORTWAVE TROUGH. THOUGH
VERTICAL SHEAR IS STRONG...INSTABILITY IS VERY LIMITED AND ANY
SEVERE THREAT SHOULD REMAIN LIMITED TO A STRONG WIND GUST OR TWO
NEXT COUPLE HOURS.
..DIAL.. 03/31/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT TUE MAR 31 2009/
...GULF COAST AREA TODAY...
AN OCCLUDED CYCLONE OVER NW IA WILL LIFT SLOWLY NEWD ACROSS MN/NW WI
THROUGH TONIGHT. A TRAILING COLD FRONT WILL CONTINUE EWD ACROSS THE
MS AND LOWER OH VALLEYS...WHILE A MARINE WARM FRONT WILL ATTEMPT TO
LIFT SLOWLY NWD ACROSS THE N CENTRAL/NE GULF COAST AND N FL. A
COMPLICATING FACTOR ACROSS THE GULF COAST WILL BE THE EXPECTED
WIDESPREAD NATURE OF THE CONVECTION...WHICH MAY INTERFERE WITH THE
NWD PROGRESSION OF THE WARM FRONT AND INLAND PENETRATION OF THE WARM
SECTOR. AT THE SAME TIME...LOW-LEVEL SHEAR IS EXPECTED TO VEER TO
MORE SWLY AND GRADUALLY WEAKEN DURING THE AFTERNOON...FIRST OVER LA
AND LATER TODAY OVER SRN AL. DEEP LAYER VERTICAL SHEAR AND
INSTABILITY /MLCAPE OF 750-1500 J/KG/ WILL BE SUFFICIENT FOR
ORGANIZED SEVERE STORMS...INCLUDING SUPERCELLS AND EMBEDDED BOW
ECHOES. DAMAGING WINDS AND LARGE HAIL WILL BE THE PRIMARY SEVERE
THREATS...THOUGH AN ISOLATED TORNADO OR TWO COULD STILL OCCUR
/PRIMARILY WITH SUPERCELLS ALONG THE WARM FRONT WHERE SOMEWHAT
STRONGER LOW-LEVEL SHEAR PERSISTS INTO THIS AFTERNOON INVOF SRN
AL/FL PANHANDLE.
THE CONVECTION SHOULD EVOLVE INTO ONE OR MORE CLUSTERS DURING THE
AFTERNOON/EVENING...AND LIKELY PERSIST INTO TONIGHT ACROSS THE NE
GULF COAST AS THE COLD FRONT STALLS AND A 30 LLJ MAINTAINS MOIST
INFLOW FROM THE ERN GULF. INSTABILITY WILL NOT BE PARTICULARLY
STRONG GIVEN THE EXPECTED IMPACTS OF PRIOR CONVECTION AND WEAK MID
LEVEL LAPSE RATES...BUT LOW-LEVEL SHEAR COULD BE STRONG ENOUGH TO
SUPPORT AN ISOLATED TORNADO THREAT EVEN OVERNIGHT.
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