SWODY1
SPC AC 260607
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0107 AM CDT THU APR 26 2007
VALID 261200Z - 271200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE NCNTRL GULF COAST NWD
ACROSS THE OH VALLEY MIDWEST AND EWD ACROSS THE SRN APPALACHIANS TO
NC/VA BORDER AREAS...
..SYNOPSIS...
VIGOROUS DEEP-LAYER CLOSED CYCLONE NOW MOVING ACROSS THE LOWER
MISSOURI RIVER VALLEY IS FORECAST TO OPEN AND ACCELERATE NEWD TOWARD
THE OH VALLEY/APPALACHIANS AND ERN GREAT LAKES THIS PERIOD. AS
SURFACE LOW ASSOCIATED WITH THIS LARGE SCALE TROUGH TRACKS FROM THE
MID MS VALLEY ACROSS THE MIDWEST THROUGH THE DAY...STRONG WARM
FRONT...CURRENTLY NEAR AND ALIGNED WITH THE OH RIVER...WILL LIFT
NEWD ACROSS PARTS OF INDIANA...OH...AND WRN PA ALLOWING MOIST WARM
SECTOR TO EXPAND ACROSS THESE AREAS. AS THE UPPER TROUGH PIVOTS
ACROSS THE OH VALLEY/MIDWEST...BELT OF STRONG WLY MID AND UPPER
LEVEL FLOW WILL ASSIST IN RELATIVELY FAST EWD PROGRESSION OF THE
SYNOPTIC COLD FRONT...ACROSS THE TN VALLEY THROUGH TONIGHT...AND
INTO THE SRN/CNTRL APPALACHIANS BY EARLY FRIDAY.
WHILE FAST WLY AND LOWER AMPLITUDE FLOW WILL EVOLVE IN THE WAKE OF
THE ERN TROUGH ACROSS THE LOWER MS VALLEY AND SOUTH...A PAIR OF
SHORT WAVE TROUGHS WILL RESULT IN PATTERN AMPLIFICATION ACROSS THE
ROCKIES AND SOUTHWEST. A POSITIVE TILT LARGE SCALE TROUGH ORIENTED
FROM THE SOUTHWEST TO NRN PLAINS WILL EVOLVE DURING THE PERIOD AS A
NRN BRANCH IMPULSE TRACKS FROM THE ROCKIES TO ERN MT/WY...AND THE
OTHER IMPULSE...NOW OVER CA...DIGS SEWD ACROSS THE LOWER CO RIVER
VALLEY.
..MIDWEST/OH VALLEY...
POTENTIAL WILL EXIST FOR SOME BOUNDARY LAYER DESTABILIZATION IN
ADVANCE OF THE SURFACE LOW/UPPER TROUGH...AND ALONG AND SOUTH OF THE
WARM FRONT FROM IL/IND...EWD ACROSS NRN KY AND OH DURING THE
AFTERNOON. MESOSCALE FORCING FOR ASCENT ALONG THE LOW LEVEL FEATURES
WILL BE FURTHER ENHANCED BY STRENGTHENING DYNAMICS AS SMALLER SCALE
MID LEVEL IMPULSES...EMBEDDED WITHIN THE LARGER TROUGH...ROTATE
ACROSS THE REGION DURING THE DAY. DESPITE MOIST BOUNDARY LAYER
EXPANDING ACROSS THE AREA AND SUPPORTING GREATER DESTABILIZATION...
WIDESPREAD CLOUD COVER MAY LIMIT HEATING. NONETHELESS...MLCAPE TO
500 J/KG...AND SOME POCKETS OF GREATER INSTABILITY IF SUN BREAKS
THROUGH...WILL PROMOTE AREAS OF MORE ROBUST CONVECTION...IN BANDS
AND CLUSTERS. STRONG DEEP-LAYER FLOW...AND LOCALLY GREATER SHEAR
NEAR THE FRONTAL ZONE COULD LEAD TO MORE ORGANIZED/PERSISTENT CELLS
WITH A CHANCE FOR HAIL AND A TORNADO OR TWO. LOW-TOPPED MULTICELL
STORMS...AND PERHAPS A FEW SUPERCELLS PRODUCING HAIL AND/OR A BRIEF
TORNADO...ALSO APPEAR POSSIBLE NEAR THE LOW CENTER...ACROSS IL/IND
AREA DURING THE AFTERNOON.
IF STRONGER HEATING THAN CURRENTLY EXPECTED CAN OCCUR OVER A LARGER
AREA FROM KY ACROSS IL/IND/OH...A GREATER RISK OF MORE WIDESPREAD
SEVERE TSTMS MAY EVOLVE. THESE AREAS WILL NEED TO BE MONITORED
CLOSELY AFTER DAYBREAK FOR THIS POTENTIAL.
..TN/AL TO GA/APPALACHIANS...
PRE-FRONTAL WARM CONVEYOR BELT WILL CONTINUE TO SUPPORT A BAND OF
ACTIVE CONVECTION ACROSS THE TN VALLEY AND DEEP SOUTH TODAY. THIS
ACTIVITY WILL PROBABLY EVOLVE FROM ONGOING STORMS ACROSS THE LOWER
MS VALLEY AREA ATTM. DESPITE WEAK LAPSE RATES...EXPECT A GRADUAL
INCREASE IN BOTH COVERAGE AND INTENSITY AS CONVECTION ENCOUNTERS
DESTABILIZING MOIST BOUNDARY LAYER FROM SRN AL ACROSS NRN GA AND ERN
TN THROUGH THE AFTERNOON AND INTO THE EVENING. LARGE SCALE HEIGHT
FALLS LIFT AWAY FROM SRN PARTS OF THE REGION BUT MID LEVEL DRY
INTRUSION AND STRONG DEEP-LAYER FLOW WILL CONTRIBUTE TO BOTH RAPID
STORM MOTION AND ENHANCED POTENTIAL FOR DAMAGING WINDS.
ADDITIONALLY...SOME HAIL AND A BRIEF TORNADO CANNOT BE COMPLETELY
RULED OUT PRIOR TO COLD FRONTAL PASSAGE.
..NC/VA...
WHILE RESIDUAL DRY CONTINENTAL POLAR AIR MASS RESIDES ACROSS
INTERIOR SECTIONS OF WRN VA AND NC...BACK-DOOR FRONT STALLED NEAR
THE NC/VA BORDER AREA WILL PROVIDE A FOCUS FOR MOISTURE CONVERGENCE
AND MODEST DESTABILIZATION THROUGH THE AFTERNOON HOURS AS STRONGER
UPPER FORCING BEGINS TO MOVE TOWARD THE REGION FROM THE WEST. RECENT
GUIDANCE HAS MIXED SIGNALS WITH RESPECT TO STORM DEVELOPMENT AND
COVERAGE ACROSS THE AREA WITH NAM-WRF SUGGESTING MORE VIGOROUS
DEEP-LAYER LIFT ALONG THE ERN SLOPES OF THE APPALACHIANS...AND GFS
AND SREF INDICATING MORE POTENTIAL FOR STORM DEVELOPMENT EWD ALONG
THE FRONTAL ZONE. PREFER THE LATTER POSSIBILITY WITH LOCALLY STRONG
INSTABILITY POSSIBLE SOUTH OF THE BOUNDARY...ACROSS NCNTRL/NERN
NC...FUELING TSTM DEVELOPMENT AS MID LEVEL FLOW AND LARGE SCALE LIFT
STRENGTHEN. A FEW STORMS COULD BE SEVERE WITH HAIL/WIND IN THE WARM
SECTOR...AND ANY ACTIVITY NEAR OR CROSSING THE FRONT POSING A LOW
PROBABILITY/BRIEF TORNADO THREAT.
.CARBIN/GUYER.. 04/26/2007
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