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Dec 20, 2013 1730 UTC Day 2 Convective Outlook

December 20, 2013

Dec 20, 2013 1730 UTC Day 2 Convective Outlook

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DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1112 AM CST FRI DEC 20 2013

VALID 211200Z – 221200Z

…THERE IS A MDT RISK OF SVR TSTMS FROM EAST TEXAS ACROSS MUCH OF LOUISIANA…SOUTHEAST ARKANSAS…WESTERN TENNESSEE AND ALL OF WESTERN MISSISSIPPI…

…THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA FROM EAST TX THE UPPER TX GULF COAST NORTHEAST TO THE OH RIVER VALLEY…TN VALLEY AND NORTHERN GULF COAST…

…SEVERE WEATHER OUTBREAK POSSIBLE ACROSS PARTS OF THE LOWER MISSISSIPPI RIVER VALLEY ON SATURDAY…

…SYNOPSIS…
STRONG TO VERY STRONG MID AND UPPER LEVEL FLOW DOMINATES THE PRONOUNCED SPLIT FLOW UPPER AIR REGIME ACROSS THE CONUS. A POTENT SHORT WAVE TROUGH…CURRENTLY OVER THE NRN GULF OF CA…WAS PIVOTING THROUGH THE BASE OF A POSITIVE-TILT LARGER SCALE TROUGH ORIENTED SW TO NE FROM THE LOWER CO RIVER VALLEY TO THE NRN PLAINS. THIS DISTURBANCE IS FORECAST TO EJECT OUT OF THE LARGER SCALE TROUGH TOWARD DOWNSTREAM CONFLUENT FLOW ACROSS THE MIDWEST. AS THE MID-LEVEL WAVE ACCELERATES NEWD FROM WEST TX TOWARD THE MS VALLEY ON SATURDAY…500MB FLOW WILL STRENGTHEN TO AROUND 100KT ACROSS THE ARKLATEX…WHILE SSWLY LOW LEVEL JET INTENSIFIES TO 60-70KT FROM EAST TX TO THE OH VALLEY.

AT THE SFC…A SHARP QUASI-STATIONARY FRONT IS CURRENTLY BECOMING DEFINED FROM CNTRL/NERN TX TO THE OH VALLEY. AS MID/UPPER TROUGH APPROACHES LATER FRIDAY AND INTO SATURDAY LIFT ACROSS THIS BOUNDARY WILL INTENSIFY SIGNIFICANTLY. ANOMALOUSLY HIGH PW AIRMASS ALONG AND SOUTH OF THE BOUNDARY WILL CONTRIBUTE TO WIDESPREAD STRONG TO SEVERE CONVECTION. IN FACT…SEVERE STORMS ARE LIKELY TO BE ONGOING AT THE START OF THE DAY 2 PERIOD… ESPECIALLY ACROSS THE ARKLATEX. AS AFOREMENTIONED MID/UPPER WIND FIELDS INTENSIFY…THE PROSPECT FOR WIDESPREAD DAMAGING WINDS AND TORNADOES WILL INCREASE THROUGH THE MORNING AND INTO LATE AFTERNOON/EVENING FROM EAST TX TO THE LOWER OH VALLEY AND OVER THE LA/MS DELTA REGION.

…AKLATEX ACROSS LA/MS…
WHILE SBCAPE WILL BE LIMITED TO AOB 500 J/KG ACROSS THE WARM SECTOR…FORECAST SOUNDINGS EXHIBIT ABUNDANT MOISTURE AND ADEQUATE LAPSE RATES TO SUPPORT DEEP MOIST CONVECTION IN AN ENVIRONMENT CHARACTERIZED BY INCREASINGLY STRONG ASCENT AND DEEP-LAYER SHEAR. LATEST STORM SCALE GUIDANCE /WRF-ARW AND NAM4/ SHOW REMARKABLE CONSISTENCY AND DEPICT THE EVOLUTION OF A STRONGLY FORCED PRE-FRONTAL SQUALL-LINE NEAR THE TX/LA BORDER BY LATE MORNING. WITH CLOUD-BEARING MEAN WINDS AND BUNKERS STORM MOTIONS AROUND 60KT…AS WELL AS ENLARGED HODOGRAPHS CONTRIBUTING TO EFFECTIVE SRH OF 300-500 M2/S2…SEVERE WINDS AND TORNADOES APPEAR LIKELY WITH LEWP/BOW STRUCTURES EMBEDDED WITHIN THE LARGER QLCS. MESOSCALE LOWS/WAVES RIPPLING ALONG THE LINE MAY SUPPORT LOCALLY ENHANCED STRONG TORNADO POTENTIAL THROUGH THE AFTERNOON ACROSS NRN LA.

THE BROKEN LINE OF SEVERE CONVECTION WILL ADVANCE EAST ACROSS NRN LA AND THE MS RIVER THROUGH EARLY EVENING. TRAILING PORTION OF THE CONVECTIVE LINE WILL MAKE SLOWER PROGRESS EAST ACROSS SRN LA AND MAY NOT ARRIVE ACROSS THE LA/MS DELTA REGION UNTIL AFTER DARK SATURDAY EVENING. NONETHELESS…EXPECT SEVERE WIND/TORNADO THREAT TO PERSIST AFTER DARK OVER THESE AREAS.

….AR/TN TO OH VALLEY…
CONVECTIVE INSTABILITY WILL REMAIN WEAK ACROSS THESE AREAS BUT MESOSCALE FORCING FOR ASCENT WILL BE PRONOUNCED ALONG THE QUASI-STATIONARY FRONT…AND ESPECIALLY NEAR FRONTAL WAVES FORECAST TO FORM AND RIPPLE ENEWD ALONG THE FRONT THROUGH THE DAY. THIS WILL RESULT IN BOUTS OF STRONG TO SEVERE STORMS SPREADING NEWD FROM AR TO SRN IL/IND AND PERHAPS AS FAR NORTHEAST AS SWRN OH INTO THE EVENING. STORM MOTIONS IN EXCESS OF 50KT AND RELATIVELY MOIST ADIABATIC PROFILE…ALONG WITH ORGANIZING INFLUENCE FROM FRONTAL WAVES/LOWS…SHOULD SUPPORT BOWING STRUCTURES CAPABLE OF PRODUCING DAMAGING WINDS. ISOLATED/BRIEF TORNADOES MAY ALSO OCCUR COINCIDENT WITH ANY PERSISTENT FRONTAL WAVE.

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