SWODY2
SPC AC 231957
DAY 2 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0157 PM CST WED FEB 23 2011
VALID 241200Z - 251200Z
...THERE IS A MDT RISK OF SVR TSTMS LATE THU AFTN AND EVE ACROSS
MUCH OF SOUTHERN AND EASTERN ARKANSAS...PARTS OF NORTHERN
MISSISSIPPI AND WESTERN TENNESSEE...
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK
AREA...FROM PARTS OF THE SOUTHERN PLAINS THRU THE LOWER OH AND TN
VALLEYS...
CORRECTED A TIME REFERENCE OF 12Z THURSDAY TO 12Z FRIDAY IN THE
SYNOPSIS
...SYNOPSIS...
MODELS SUGGEST THAT MID/UPPER FLOW WILL REMAIN BROADLY CONFLUENT
DOWNSTREAM OF PROMINENT EASTERN PACIFIC BLOCKING THROUGH MUCH OF
NORTH AMERICA DURING THIS FORECAST PERIOD. A STRONG JET APPEARS
LIKELY TO ROUND THE CREST OF A STRENGTHENING HIGH CENTER NEAR THE
GULF OF ALASKA...WITH A RIDGE AXIS BUILDING NORTHEASTWARD INTO
WESTERN CANADA. AS THIS OCCURS...A SIGNIFICANT SHORT WAVE TROUGH IS
PROGGED TO CONTINUE SLOWLY DIGGING SOUTHWARD NEAR THE NORTHERN
PACIFIC COAST. THIS WILL CONTRIBUTE TO THE NORTHEASTWARD
ACCELERATION OF A WEAKENING CIRCULATION CENTER NOW TURNING INLAND
ACROSS NORTHERN BAJA.
DESPITE THE DEAMPLIFICATION OF THIS LATTER FEATURE...GUIDANCE
INDICATES THAT FLOW FIELDS WILL INTENSIFY TO ITS SOUTH AND EAST...AS
IT ACCELERATES ACROSS THE SOUTHERN ROCKIES...INTO AND THROUGH THE
CREST OF A BROAD UPPER RIDGE OVER THE LOWER OHIO VALLEY BY 12Z
FRIDAY. LARGE-SCALE FORCING IS PROGGED TO SUPPORT FAIRLY
SIGNIFICANT SURFACE CYCLOGENESIS FROM THE OZARK PLATEAU THROUGH THE
OHIO VALLEY LATE THURSDAY AND THURSDAY NIGHT. WITH A RETURN FLOW
ALREADY DEVELOPING OFF AN INCREASING MOIST BOUNDARY LAYER OVER THE
WESTERN GULF OF MEXICO...THIS PROBABLY WILL BE ACCOMPANIED BY
CONSIDERABLE THUNDERSTORM ACTIVITY...INCLUDING THE RISK FOR SEVERE
STORMS. BY THURSDAY EVENING...IT APPEARS THAT THERE WILL BE A
WINDOW OF OPPORTUNITY FOR THE DEVELOPMENT OF CONDITIONS FAVORABLE
FOR ONE OR TWO STRONG TORNADOES...AND STRONG DAMAGING
WINDS...PARTICULARLY ACROSS PARTS OF SOUTHERN AND EASTERN ARKANSAS
INTO PARTS OF NORTHERN MISSISSIPPI AND WESTERN TENNESSEE.
...SOUTHERN PLAINS INTO THE SOUTHERN APPALACHIANS...
LAPSE RATES IN THE WARM SECTOR OF THE DEVELOPING SURFACE CYCLONE MAY
NOT BECOME PARTICULARLY STEEP THURSDAY...AND UNCERTAINTY EXISTS
CONCERNING THE POTENTIAL STABILIZING INFLUENCE OF EARLY DAY
CONVECTION AND PRECIPITATION...PARTICULARLY NORTHEAST OF THE OZARK
PLATEAU...AS WELL AS PORTIONS OF THE SOUTHERN PLAINS.
HOWEVER...NORTHWARD MOISTURE RETURN /INCLUDING INCREASING
PRECIPITABLE WATER UP TO 1.5 INCHES/ OFF THE WESTERN GULF SHOULD
COMPENSATE SOMEWHAT...CONTRIBUTING TO AT LEAST WEAK CAPE. GIVEN MID
60S TO NEAR 70F DEW POINTS CURRENTLY PRESENT FROM THE WESTERN GULF
INTO SOUTHERN TEXAS...CURRENT MODEL PROGS MAY BE A BIT LOW ON
BOUNDARY LAYER MOISTURE RETURN INTO THE LOWER MISSISSIPPI VALLEY AND
OZARK PLATEAU BY LATE THURSDAY AFTERNOON AND EVENING.
GIVEN BOUNDARY LAYER DESTABILIZATION AND INCREASINGLY DIFLUENT/
DIVERGENT UPPER FLOW WITH THE APPROACHING MID-LEVEL PERTURBATION
...WHICH IS PROGGED TO TAKE ON AN INCREASING NEGATIVE TILT
ORIENTATION...CONDITIONS MAY BECOME FAVORABLE FOR DISCRETE STORM
DEVELOPMENT ACROSS SOUTHERN AND EASTERN ARKANSAS DURING THE 21-23Z
TIME FRAME. COINCIDING WITH STRENGTHENING OF A SOUTHERLY 850 MB JET
IN EXCESS OF 50 KTS...UP TO 70 KT OR SO DURING THE EVENING
HOURS...AND THE EVOLUTION OF LARGE CLOCKWISE CURVED LOW-LEVEL
HODOGRAPHS BENEATH/NEAR A 90-100 KT 500 MB JET... POTENTIAL EXISTS
FOR SUPERCELLS CAPABLE OF PRODUCING STRONG TORNADOES.
ANY SUCH ACTIVITY IS EXPECTED TO FORM NEAR OR IN ADVANCE OF A
FRONTAL OR PRE-FRONTAL SQUALL LINE...WHICH APPEARS MORE CERTAIN TO
EVOLVE...BEFORE ADVANCING EASTWARD ACROSS UPPER PORTIONS OF THE
LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY THURSDAY NIGHT.
POTENTIAL FOR STRONG TORNADOES MAY PERSIST THROUGH THE 03-05Z TIME
FRAME ACROSS PARTS OF NORTHERN MISSISSIPPI AND WESTERN
TENNESSEE...WHILE DAMAGING WIND POTENTIAL CONTINUES DEEPER INTO THE
NIGHT TOWARD THE SOUTHERN APPALACHIANS.
..KERR.. 02/23/2011
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