SWODY2
SPC AC 241720
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1220 PM CDT TUE APR 24 2007
VALID 251200Z - 261200Z
..THERE IS A SLGT RISK OF SVR TSTMS WED/WED NIGHT FROM PARTS OF THE
SERN PLAINS EWD THRU THE LOWER OH/TN VALLEYS AND CNTRL GULF
STATES....
..SYNOPSIS...
A BROAD CLOSED LOW/TROUGH IN THE SOUTHERN BRANCH OF SPLIT POLAR
WESTERLIES IS BEGINNING TO SHIFT EAST OF THE CENTRAL/SOUTHERN
ROCKIES. AND...MODELS INDICATE THAT THIS FEATURE WILL REMAIN
PROGRESSIVE INTO WEDNESDAY...TO THE SOUTH OF A GENERALLY ZONAL
NORTHERN STREAM EXTENDING ALONG THE CANADIAN/U.S. BORDER. LATE
WEDNESDAY/WEDNESDAY NIGHT...AMPLIFICATION IN THE UPSTREAM PATTERN
..FROM THE EASTERN PACIFIC INTO PACIFIC COASTAL AREAL AREAS...MAY
CONTRIBUTE TO THE COMMENCEMENT OF A SLOW NORTHEASTWARD ACCELERATION
OF THE SOUTHERN BRANCH SYSTEM...OUT OF THE MIDDLE/LOWER MISSISSIPPI
VALLEY.
SURFACE CYCLONE ACCOMPANYING SOUTHERN BRANCH LOW IS EXPECTED TO BE
OCCLUDED AND IN THE PROCESS OF WEAKENING BY EARLY WEDNESDAY...WITH
THE PRIMARY COLD FRONT SURGING THROUGH THE SOUTHERN PLAINS. AT
LEAST ONE...IF NOT A COUPLE...OF COOL SURGES WILL PRECEDE THIS FRONT
FROM THE SOUTHEASTERN PLAINS THROUGH THE MIDDLE/LOWER MISSISSIPPI
VALLEY. THE MOST SIGNIFICANT OF THESE...MODELS APPEAR TO
SUGGEST...WILL EXTEND FROM POINT OF OCCLUSION OVER NORTHEAST
MISSOURI...SOUTHWARD TOWARD UPPER TEXAS COASTAL AREAS BY MIDDAY
WEDNESDAY. THE BOUNDARY LAYER TO THE EAST OF THIS FRONT...AND SOUTH
OF A WARM FRONT EXTENDING EASTWARD INTO THE LOWER OHIO VALLEY...AND
ON INTO MID ATLANTIC COASTAL AREAS...IS EXPECTED TO BE VERY MOIST
WITH UPPER 60S TO NEAR 70F DEW POINTS. HOWEVER...UPPER 50S/LOWER
60S DEW POINTS WILL LIKELY PERSIST TO THE WEST...UNTIL MAIN FRONTAL
PASSAGE LATER WEDNESDAY/WEDNESDAY NIGHT.
..MID/LWR MISSISSIPPI VALLEY AND ADJACENT AREAS...
POSSIBILITY OF CONSIDERABLE CLOUD COVER...PERHAPS CONVECTION...AND
WEAKENING LOW-LEVEL FLOW FIELDS /AT LEAST EARLY IN THE DAY/ IN THE
WARM SECTOR ARE AMONG FACTORS CONTRIBUTING TO SOMEWHAT UNCLEAR
SEVERE POTENTIAL FOR THIS PERIOD. MID-LEVEL LAPSE ASSOCIATED WITH
THE SOUTHERN BRANCH TROUGH WILL BECOME WEAK...AND THIS WILL LIMIT
CAPE. PEAK MIXED LAYER CAPE MAY REMAIN BELOW 1000 J/KG ACROSS MOST
AREAS. HOWEVER...DEEP LAYER VERTICAL SHEAR ASSOCIATED WITH A 50-70+
KT SOUTH SOUTHWESTERLY 500 MB JET STREAK WILL REMAIN MORE THAN
FAVORABLE FOR SUPERCELLS...AND MOIST BOUNDARY LAYER AIR...
PARTICULARLY TO THE EAST OF LEAD WEAK COOL SURGE...WILL MAINTAIN THE
RISK FOR TORNADOES...IN ADDITION TO THE POSSIBILITY OF DAMAGING WIND
GUSTS/MARGINALLY SEVERE HAIL.
CONFIDENCE IS LOW CONCERNING ANTICIPATED CONVECTIVE EVOLUTION... BUT
IT CURRENTLY SEEMS MOST PROBABLE THAT THE BULK OF THE DEVELOPMENT
WILL OCCUR AHEAD OF INITIAL LEAD COOL SURGE...WITH A BROKEN LINE OF
STORMS INTENSIFYING ACROSS PARTS OF ARKANSAS/LOUISIANA BY THE
AFTERNOON HOURS. ISOLATED SUPERCELLS WILL PROBABLY BE EMBEDDED
WITHIN THIS LINE...AND PERHAPS DEVELOP IN ADVANCE...AS ACTIVITY
SPREADS EASTWARD.
MODELS ARE SUGGESTIVE THAT A PRE-FRONTAL SOUTHERLY LOW-LEVEL JET MAY
RE-INTENSIFY SOMETIME LATE WEDNESDAY OR WEDNESDAY NIGHT...AS THE
MID/UPPER TROUGH BEGINS TO TAKE ON AN INCREASINGLY NEGATIVE TILT
PRIOR TO ACCELERATING NORTHEASTWARD. IF/WHEN THIS DOES
OCCUR...ENLARGING LOW-LEVEL HODOGRAPHS WILL SUPPORT INCREASING
TORNADIC POTENTIAL ACROSS THE CENTRAL GULF STATES INTO THE TENNESSEE
VALLEY...INCLUDING THE POSSIBILITY OF ISOLATED STRONG TORNADOES.
.KERR.. 04/24/2007
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