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Dec 21, 2013 2000 UTC Day 1 Convective Outlook

December 21, 2013

Dec 21, 2013 2000 UTC Day 1 Convective Outlook

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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0159 PM CST SAT DEC 21 2013

VALID 212000Z – 221200Z

…THERE IS A MDT RISK OF SVR TSTMS FROM NORTHEAST LOUISIANA ACROSS NORTHERN AND CENTRAL MISSISSIPPI TO MIDDLE TENNESSEE AND SOUTHERN KENTUCKY…

…THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA FROM EXTREME ERN TX TO THE OH VALLEY AND SOUTH TO THE NRN GULF COAST….

…LOWER MS TO OH VALLEY…
LONG ADVERTISED NEGATIVE-TILT SHORTWAVE TROUGH WAS CROSSING THE RED RIVER FROM TX INTO OK THIS AFTERNOON WITH ATTENDANT 100KT 500MB/6KM JET RECENTLY OBSERVED IN FDR VWP DATA. IN RESPONSE TO THIS VIGOROUS MID-LEVEL DISTURBANCE…A NUMBER OF WEAK FRONTAL WAVES HAVE TAKEN FORM AND RIPPLED NNE ALONG THE SHARP BAROCLINIC ZONE SITUATED FROM EAST-CNTRL TX TO SERN AR TO THE OH VALLEY. SO FAR IT SEEMS THAT THESE FRONTAL WAVE DISTURBANCES HAVE INTRODUCED COMPLEXITY TO THE SEVERE FCST AS NO SINGLE STRONGER LOW HAS YET TO TAKE FORM AND BECOME THE PRIMARY FOCUS FOR SUBSEQUENT SEVERE STORM DEVELOPMENT. THAT MAY BE ABOUT CHANGE AS STRONGER DEEP-LAYER FORCING FOR ASCENT NOW APPEARS TO BE SPREADING EAST FROM TX WITH A COINCIDENT AND GRADUAL INCREASE IN COHERENT STORM UPDRAFTS AND LIGHTNING ACTIVITY OCCURRING FROM NORTH OF HOUSTON TO SRN AR OVER THE LAST HOUR.

SHORT-TERM SCENARIOS INTO THIS EVENING HAVE PRIMARY WAVE CYCLONE CONTINUING TO TRACK NEWD ALONG THE FRONT FROM AR TO THE OH VALLEY. WARM/MOIST CONVEYOR BELT ALONG AND IMMEDIATELY EAST OF THE LOW TRACK WILL CONTINUE TO SUPPORT DEEP CONVECTION AMIDST INTENSE AND STRENGTHENING LOW THROUGH MID-LEVEL FLOW FIELDS. WEAK CAPPING OBSERVED IN LCH/LIX AND JAN 18Z SOUNDINGS SHOULD ERODE AS DEEP-LAYER ASCENT CONTINUES TO ACT ON THE MARGINALLY UNSTABLE WARM SECTOR AIRMASS. ESSENTIALLY TWO ZONES OF MORE ORGANIZED TSTMS ARE EXPECTED TO CONTINUE TO EVOLVE WITH THIS SYSTEM.

…AR/TN TO OH VALLEY…
STORM SCALE GUIDANCE…INCLUDING THE LATEST HRRR…CONTINUE TO SUPPORT SOME CONSOLIDATION/INTENSIFICATION OF CONVECTION NEAR AND AHEAD THE FRONTAL WAVE FROM ERN AR NORTH ALONG THE MS RIVER TO THE OH RIVER INTO THIS EVENING. AS STRONGER LARGE SCALE FORCING AND SHEAR SPREAD TOWARD/ACROSS THESE AREAS INTO THE EVENING…EXPECT SOME INCREASE IN TSTM VIGOR AND ORGANIZATION WITH PROSPECTS FOR FAST-MOVING LINE SEGMENTS CAPABLE OF PRODUCING DAMAGING WINDS. A RELATIVELY WARM/MOIST BOUNDARY LAYER EXISTS ALONG AND SOUTH OF THE OH RIVER AND SHOULD SUPPORT THE SEVERE WIND TSTM WIND POTENTIAL INTO THE NIGHT GIVEN THE MAGNITUDE OF THE FORCING AND SHEAR FORECAST TO DEVELOP ACROSS THE REGION DURING THIS TIME.

…ARK/LA/MS TO TN VALLEY LATE…
LATEST TRENDS SUPPORT A CONTINUATION OF A SIGNIFICANT TORNADO FORECAST WITH A SMALL REDUCTION IN OVERALL TORNADO PROBABILITIES. GIVEN MIXED TO LINEAR STORM MODE NOW BEING OBSERVED ON RADAR FROM THE SABINE PASS TO NRN LA…AND THE LIKELY TRANSITION TO INCREASINGLY LINEAR MODE AS FRONTAL ADVANCE OCCURS IN THE WAKE OF THE FRONTAL WAVE PASSAGE…EXPECT THE WIND DAMAGE THREAT TO RAMP UP AND REMAIN PROMINENT INTO THE EVENING FROM LA INTO EXTREME SERN AR AND NWRN MS. HOWEVER…BOTH RAP AND RAP2 INDICATE A NARROW CORRIDOR OF HIGH EFFECTIVE SRH NEARING 500 M2/S2 COINCIDENT WITH A RIBBON OF NEAR 70 F DEWPOINTS IMMEDIATELY AHEAD OF THE FRONT ATTM. THIS VOLATILE ENVIRONMENT WILL CERTAINLY SUPPORT FAST-MOVING LONGER-LIVED LINE SEGMENTS WITH THE POTENTIAL FOR EMBEDDED SUPERCELL/QLCS TORNADOES…POTENTIALLY STRONG…OVER THE NEXT FEW HOURS. A TREND TOWARD A MORE SOLID SQLN MAY OCCUR LATER TONIGHT WITH THE LOWER PROBABILITY WIND THREAT CONTINUING EAST TO THE TN VALLEY/NRN AL.

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