SPC AC 270610
   
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0110 AM CDT WED APR 27 2011
   
VALID 271200Z - 281200Z
   
...THERE IS A HIGH RISK OF SVR TSTMS OVER PORTIONS OF NRN
MS...AL...FAR NWRN GA AND SRN MIDDLE TN...
   
...THERE IS A MDT RISK OF SVR TSTMS OVER MUCH OF CNTRL AND NRN MS
AND AL...NWRN GA...MUCH OF TN AND KY...WRN CAROLINAS...
   
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER MS VALLEY/GULF
COAST STATES NWD TO THE CANADIAN BORDER...
   
CORRECTED FOR SPELLING ERROR
   
...SYNOPSIS...
AN UPPER TROUGH AXIS WILL BE CENTERED ACROSS THE SRN PLAINS AT 12Z
WED...WITH A 100 KT MID LEVEL JET ACROSS N TX. THIS FEATURE WILL
STRENGTHEN THROUGH 00Z AS IT EJECTS NEWD ACROSS THE LOWER MS AND
INTO THE TN/OH VALLEYS DURING THE DAY. AT THE SURFACE...LOW PRESSURE
IS FORECAST TO BE OVER W CNTRL AR AT 12Z...WITH A DEVELOPING COLD
FRONT TRAILING SWWD INTO ERN TX. THESE FEATURES WILL MOVE RAPIDLY
ENEWD...WITH THE SURFACE LOW NEARING SRN INDIANA BY 00Z AND A SHARP
LOW PRESSURE TROUGH EXTENDING SWD INTO CNTRL KY...MIDDLE TN...ERN MS
AND WRN AL.
   
AHEAD OF THE FRONT...A VERY WARM AND MOIST AIR MASS WILL ALREADY BE
IN PLACE BY MIDDAY WITH 68-72 BOUNDARY LAYER DEWPOINTS LIKELY FROM
THE GULF COAST INTO MS/AL...AND MID TO UPPER 60S F OVER TN AND SRN
KY WHERE SUBSTANTIAL MORNING CONVECTION WILL LIKELY BE ONGOING. WITH
RELATIVELY COOL TEMPERATURE PROFILES ALOFT...AN EXTREMELY UNSTABLE
ATMOSPHERE WILL RESULT ACROSS THE WARM SECTOR. WIND FIELDS
THROUGHOUT THE TROPOSPHERE WILL STRENGTHEN WITH THE APPROACHING
TROUGH/JET MAX...AND THE COMBINATION OF THE TWO IS EXPECTED TO
RESULT IN A TORNADO OUTBREAK...WITH LONG-TRACKED STRONG TO VIOLENT
TORNADOES POSSIBLE OVER THE HIGH RISK AREA.
   
TO THE E...THE BROAD SLY FLOW ACROSS THE WARM SECTOR WILL EXTEND
INTO THE MID ATLANTIC REGION...WITH A SECONDARY MOIST PLUME OFF THE
ATLANTIC NWD INTO THE CAROLINAS AND WRN VA BY AFTERNOON.
   
--- AN OUTBREAK OF TORNADOES AND DAMAGING WINDS IS EXPECTED TODAY
THROUGH EVENING OVER PORTIONS OF NRN MS...NRN AL...TN AND KY. ---
   
...LOWER MS VALLEY INTO TN/OH VALLEYS...
A COMPLICATED FORECAST SCENARIO WILL UNFOLD TODAY...BEGINNING RATHER
EARLY IN THE PERIOD OVER SRN AND ERN AR AND NRN LA. MODELS ARE IN
RELATIVELY GOOD AGREEMENT WITH THE PLACEMENT OF THE SURFACE LOW OVER
AR BETWEEN 12-15Z...THEN DEVELOPING IT NEWD ACROSS TN/KY BY 00Z.
NUMEROUS THUNDERSTORMS WILL BE ONGOING...AND SOME WILL BE
SEVERE...FROM NRN LA/SRN AR EWD ACROSS NRN MS...WRN AND MIDDLE TN
AND KY. DESPITE TIME OF DAY...PRESENCE OF RICH LOW LEVEL MOISTURE
WILL RESULT IN LITTLE CAPPING AND SURFACE BASED EFFECTIVE PARCELS. 
THUS...A TORNADO AND DAMAGING WIND THREAT WILL BE PRESENT WITH THIS
ACTIVITY.
   
SOUTH OF THE ONGOING ACTIVITY...STRONG DAYTIME HEATING WILL OCCUR.
WITH BOUNDARY LAYER DEWPOINTS IN THE LOW 70S F...THIS WILL CREATE
STRONG TO EXTREME INSTABILITY OVER MS AND AL NWD TO THE ONGOING
CONVECTION. A CAPPING INVERSION WILL LIKELY KEEP MUCH OF THE WARM
SECTOR S OF THE EARLY STORMS CAPPED...ALLOWING A BUILD UP OF
INSTABILITY TO BE RELEASED WHEN LARGE SCALE FORCING ARRIVES DURING
THE AFTERNOON ALONG THE COLD FRONT AND ESPECIALLY NEAR THE
FRONT/OUTFLOW BOUNDARY INTERSECTION. THE RESULT WILL BE FAST MOVING
TORNADIC SUPERCELLS CAPABLE OF STRONG TO VIOLENT TORNADOES. GIVEN
THE FAST STORM MOTIONS AND RELATIVELY WIDE WARM SECTOR...SOME
TORNADOES COULD BE LONG LIVED. THE GREATEST THREAT FOR THESE TYPES
OF STORMS WILL BE OVER THE HIGH RISK AREA...OVER NRN MS AND
AL...INTO EXTREME NWRN GA AND SRN MIDDLE TN. THIS ACTIVITY WILL
PERSIST TO THE E...BUT CELLS MAY EVENTUALLY MERGE INTO MORE OF A
QLCS STRUCTURE CAPABLE OF PARTICULARLY DAMAGING WINDS AND A FEW
TORNADOES.
   
...WRN NC/VA...
A CONDITIONAL SEVERE THREAT WILL EXIST BY LATE AFTERNOON OVER WRN
NC/VA.  STRONG  HEATING WILL RESULT IN STEEP LOW LEVEL LAPSE
RATES...BUT FORECAST SOUNDINGS SHOW A CAPPING INVERSION AROUND 700
MB...WHICH SHOULD KEEP THE AIR MASS CAPPED. HOWEVER...MOISTURE
ADVECTION...AS WELL AS SELY UPSLOPE FLOW MAY RESULT IN ISOLATED
THUNDERSTORMS DURING THE AFTERNOON OVER THE HIGHER TERRAIN. WIND
PROFILES WOULD FAVOR SUPERCELLS...CAPABLE OF PRODUCING TORNADOES
HAIL AND WIND. WILL MAINTAIN LOW PROBABILITIES FOR THE DAYTIME
CONVECTION.
   
..JEWELL.. 04/27/2011
   
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