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Dec 20, 2013 0700 UTC Day 2 Convective Outlook

December 20, 2013

Dec 20, 2013 0700 UTC Day 2 Convective Outlook

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DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CST FRI DEC 20 2013

VALID 211200Z – 221200Z

…THERE IS A MDT RISK OF SVR TSTMS FOR PORTIONS OF THE LOWER MS VALLEY…

…THERE IS A SLGT RISK OF SVR TSTMS FROM THE WRN/CNTRL GULF COAST NEWD ACROSS THE LOWER MS AND OH VALLEYS…

THE POTENTIAL EXISTS FOR SIGNIFICANT AND WIDESPREAD DAMAGING WINDS AND A FEW TORNADOES…ESPECIALLY ACROSS PARTS OF THE LOWER MS VALLEY.

…SYNOPSIS…
AN UPPER TROUGH WILL ACCELERATE NEWD OUT OF THE SRN HIGH PLAINS WHILE ACQUIRING A NEGATIVE-TILT BEFORE APPROACHING THE MID-MS VALLEY. A SUBSEQUENT STRENGTHENING OF DEEP-LAYER WIND FIELDS WILL OCCUR…WITH A VERY STRONG LOW-LEVEL JET BECOMING ESTABLISHED FROM THE CENTRAL GULF COAST INTO THE UPPER OH VALLEY BY AFTERNOON. AT THE SFC…A STALLED FRONT WILL EXTEND FROM THE ARKLATEX AND ALONG THE OH VALLEY…WITH A MOIST GULF AIR MASS SPREADING INLAND S OF THE FRONT. A LOW WILL DEVELOP OUT OF CNTRL TX AND TRACK NEWD NEAR THE POSITION OF THE STALLED FRONT…WHILE AN ATTENDANT COLD FRONT SWEEPS EWD.

…WRN/CNTRL GULF COAST NEWD ACROSS THE LOWER MS AND OH VALLEYS…

OBSERVATIONAL DATA SHOW RICH GULF MOISTURE BEGINNING TO ADVECT NWD ACROSS THE GULF COASTAL AREAS…WITH DEWPOINTS IN THE UPPER 60S-LOWER 70S F LOCATED JUST OFFSHORE. MOISTURE WILL CONTINUE TO SPREAD INLAND OVER THE NEXT 24 HRS…AS A COLD FRONT STALLS FROM CENTRAL TX NEWD ACROSS THE ARKLATEX INTO THE LOWER OH VALLEY…RESULTING IN A BROAD WARM SECTOR CHARACTERIZED BY A SEASONABLY MOIST AIR MASS. WIDESPREAD CONVECTION IS LIKELY TO DEVELOP ALONG THE STALLED FRONT PRIOR TO THE START OF THE D2 PERIOD AND PERSIST INTO THE DAYTIME ON SAT. A SFC LOW WILL DEVELOP OUT OF CNTRL TX AND INTO THE ARKLATEX DURING THE MORNING…AND ACROSS AR/LOWER OH VALLEY LATER IN THE AFTERNOON/EVENING. AN ATTENDANT COLD FRONT WILL SLOWLY MOVE EWD ACROSS E TX AND LA/AR…BEFORE REACHING THE LOWER MS VALLEY DURING THE EVENING…AND WILL LIKELY FOSTER AN EWD SHIFT IN CONVECTIVE DEVELOPMENT WITH TIME.

THE UPPER TROUGH EJECTING OUT OF THE SRN PLAINS WILL BECOME NEGATIVELY-TILTED WITH NEWD PROGRESSION. STRONGEST MID-/UPPER-LEVEL FORCING FOR ASCENT ASSOCIATED WITH THE TROUGH WILL BE FOCUSED ACROSS THE SRN OZARKS AND POINTS NEWD…MAINLY ALONG/N OF THE STALLED FRONT AND SFC LOW. MEANWHILE…LATEST SUITE OF DETERMINISTIC/ENSEMBLE FORECAST MODEL GUIDANCE IS MORE CONSISTENT DEPICTING THE EVOLUTION OF CONVECTION DEVELOPING ALONG A PRE-FRONTAL TROUGH DURING THE AFTERNOON. INITIALLY…THIS ACTIVITY WILL LIKELY BE FOCUSED ACROSS LA AND SRN AR AND EVENTUALLY SHIFTING E OF THE MS VALLEY DURING THE EVENING.

LOW-LEVEL WINDS/SHEAR WILL INTENSIFY GREATLY DURING THE FIRST HALF OF THE D2 PERIOD…WITH ASSOCIATED WIND PROFILES SUFFICIENT FOR SUPERCELLS WITH THE POTENTIAL FOR DMGG WINDS/TORNADOES. THE MAGNITUDE OF EACH INDIVIDUAL THREAT WILL BE DEPENDENT ON THE CONVECTIVE MODE EVOLUTION. TSTMS MAY TREND TOWARDS LINEAR INVOF BOTH THE STALLED FRONT AND COLD FRONT. A MIX OF QUASI-LINEAR AND CLUSTER MODES MAY EXIST FARTHER S WITH PRE-FRONTAL CONVECTION ACROSS THE LOWER MS VALLEY…WHERE BOTH LOW-LEVEL CONVERGENCE AND UPPER-LEVEL FORCING FOR ASCENT ARE COMPARATIVELY WEAKER…BUT MERIDIONAL WIND PROFILES WILL PROMOTE STORM INTERACTIONS/MERGERS. AN ENHANCED TORNADO THREAT MAY ACCOMPANY ANY DISCRETE OR CLUSTER TSTMS THAT CAN DEVELOP AHEAD OF THE CONVECTIVE LINE…ESPECIALLY ACROSS THE LOWER MS VALLEY.

PRIMARY UNCERTAINTIES/LIMITATIONS AT THIS TIME ARE THE SOMEWHAT MARGINAL BUOYANCY/MIDLEVEL LAPSE RATES THROUGHOUT THE WARM SECTOR /PARTIALLY OWING TO LIMITED DAYTIME HEATING/…AND CONVECTIVE MODE EVOLUTION. BUOYANCY DECREASES MARKEDLY FARTHER N INTO THE OH RIVER VALLEY…BUT STRONG WIND PROFILES MAY CONTINUE TO SUPPORT A DMGG WIND AND ISOLATED TORNADO THREAT OVERNIGHT ALONG/AHEAD OF THE SFC LOW TRACKING NEWD. FARTHER S…PRIMARY SFC LOW AND UPPER TROUGH WILL BECOME WELL SEPARATED FROM THE WARM SECTOR OVERNIGHT…BUT CONVECTION SHOULD PERSIST IN SOME FORM /BROKEN LINE AND/OR CLUSTERS/ ACROSS THE CNTRL GULF STATES INTO THE TN VALLEY. THE ENVIRONMENT WILL REMAIN FAVORABLE FOR DMGG WIND GUSTS AND AN ISOLATED TORNADO THREAT WITH STRONG LOW-LEVEL SHEAR AND SFC-BASED PARCELS.

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