SWODY1
SPC AC 201630
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CDT TUE MAR 20 2012
VALID 201630Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR
EXTREME SE TX...WRN LA...AND SRN/CENTRAL AR...
...SE TX/WRN LA INTO SRN/CENTRAL AR THROUGH TONIGHT...
AN EXTENSIVE N-S SQUALL LINE CONTINUES TO MOVE SLOWLY EWD FROM E/SE
TX INTO WRN LA...WITH WEAKER/SHALLOWER CONVECTION ALONG THE OUTFLOW
BOUNDARY FARTHER N INTO SRN/CENTRAL AR. A MOIST/MODERATELY UNSTABLE
AIR MASS CONTINUES IN ADVANCE OF THE SQUALL LINE WITH MID-UPPER 60S
BOUNDARY LAYER DEWPOINTS...AND ASCENT ALONG THE LEADING EDGE OF THE
OUTFLOW WILL CONTINUE TO INITIATE NEW STORMS THROUGH THE AFTERNOON.
DEEP-LAYER SLY FLOW WITH EFFECTIVE BULK SHEAR OF 40-50 KT AND
EFFECTIVE SRH OF 200-300 M2/S2 WILL CONTINUE TO SUPPORT A RISK FOR
CIRCULATIONS WITHIN THE LINE CAPABLE OF PRODUCING A COUPLE OF
TORNADOES AS WELL AS DAMAGING GUSTS THROUGH THIS EVENING. LOCALLY
HEAVY RAINFALL WILL REMAIN A CONCERN WITH TRAINING CONVECTION AND
ONLY SLOW EWD MOTION OF THE LINE.
...MO AREA THIS AFTERNOON/EVENING...
BOUNDARY LAYER MOISTURE DIMINISHES WITH NWD EXTENT FROM LA TO
MO...THOUGH SURFACE HEATING AND DEWPOINTS OF 58-60 F WILL HELP
GENERATE WEAK INSTABILITY THIS AFTERNOON INTO CENTRAL MO/ E OF THE
THICK CLOUD BAND AND REMNANT OUTFLOW BOUNDARY/. A WEAK SURFACE LOW
IS LOCATED NEAR THE SW MO/NW AR BORDER AS OF 15Z...BUT THE 12Z NAM
APPEARS TO BE SUFFERING FROM CONVECTIVE FEEDBACK AND IS LIKELY TOO
STRONG WITH ITS WAVE AND POCKET OF ENHANCED LOW-LEVEL SHEAR MOVING
NWD FROM WRN AR THIS AFTERNOON TO WRN MO THIS EVENING. WILL
MAINTAIN LOW WIND/TORNADO PROBABILITIES...BUT INSTABILITY AND
UNCERTAINTIES IN CONVECTIVE EVOLUTION PRECLUDE THE NEED FOR A
CATEGORICAL UPGRADE.
...SW OK/NW TX THIS AFTERNOON/EVENING...
EMBEDDED SPEED MAXIMA ARE ROTATING AROUND THE SRN/ERN PERIPHERY OF
THE CLOSED MIDLEVEL LOW OVER THE NM/TX BORDER...AND THE PRIMARY
SURFACE REFLECTION OF THIS LOW IS A CYCLONE IN THE NE TX PANHANDLE.
A SURFACE TROUGH EXTENDS SEWD FROM THE LOW INTO NW TX...AND THE LOW
IS FORECAST TO PIVOT SEWD THIS AFTERNOON. SURFACE HEATING WILL
CONTRIBUTE TO DESTABILIZATION ALONG THE TROUGH AND NEAR THE LOW THIS
AFTERNOON...DESPITE BOUNDARY LAYER DEWPOINTS ONLY IN THE 40S. COLD
TEMPERATURES ALOFT AND STEEP LOW-LEVEL LAPSE RATES WILL SUPPORT A
BROKEN ARC OF LOW-TOPPED STORMS THIS AFTERNOON/EVENING FROM NW TX
INTO SW OK...WHERE THE STRONGEST/DEEPEST STORMS MAY PRODUCE HAIL.
...VA/NC THIS AFTERNOON/EVENING...
NO CHANGES TO PREVIOUS FORECAST REASONING WITH THE POTENTIAL FOR A
FEW MARGINALLY SEVERE STORMS THIS AFTERNOON AS INSTABILITY
INCREASES.
..THOMPSON/LEITMAN.. 03/20/2012
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