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Apr 29, 2014 1300 UTC Day 1 Convective Outlook

April 29, 2014

Apr 29, 2014 1300 UTC Day 1 Convective Outlook

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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0745 AM CDT TUE APR 29 2014

VALID 291300Z – 301200Z

…THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT ACROSS PARTS OF MS AND AL…

…THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES SWD TO CNTRL AND ERN GULF COAST AND EWD TO THE CAROLINAS AND VA…

…SUMMARY…
SCATTERED TO NUMEROUS SEVERE THUNDERSTORMS WILL AFFECT PORTIONS OF THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS INTO CENTRAL AND EASTERN GULF STATES THIS AFTERNOON INTO TONIGHT. SEVERAL TORNADOES…A FEW OF WHICH COULD BE STRONG…VERY LARGE HAIL AND STRAIGHT LINE DAMAGING WINDS APPEAR LIKELY.

…SYNOPSIS…

A MID TO UPPER-LEVEL LOW CENTERED OVER THE MIDWEST MAY PIVOT SLIGHTLY NWD DURING THE DAY ONE PERIOD IN RESPONSE TO A NUMBER OF VORTICITY MAXIMA ROTATING AROUND IT/S PERIPHERY. OF CONSEQUENCE TO SEVERE WEATHER POTENTIAL…A BROAD CYCLONIC BELT OF STRONG 500-MB WINDS WILL BE MAINTAINED FROM THE SRN ROCKIES THROUGH SRN PLAINS…LOWER MS/TN VALLEYS…INTO THE UPPER OH VALLEY AND LOWER GREAT LAKES. EMBEDDED WITHIN THIS HIGH-MOMENTUM AIR STREAM…EARLY MORNING WATER VAPOR IMAGERY AND TIME-HEIGHT VAD DATA FROM THE SRN PLAINS INDICATE A DISTINCT 70-80 KT JET STREAK AT 6 KM AGL WHICH WILL PROGRESS EWD TODAY THROUGH THE ARKLATEX INTO LOWER MS VALLEY…ENHANCING VERTICAL SHEAR AND FORCING FOR ASCENT.

AT THE SURFACE…AN OCCLUDED SURFACE LOW OVER SERN IA WILL GRADUALLY WEAKEN WHILE DEVELOPING NEWD INTO SRN OR CNTRL WI WHILE AN ASSOCIATED COLD FRONT SLOWLY SHIFTS FROM THE MS VALLEY EWD INTO OH/TN VALLEYS AND CNTRL GULF STATES. A SECONDARY LOW PRESSURE CENTER IS FORECAST TO DEVELOP ALONG THE SRN SEGMENT OF THE COLD FRONT OVER MS TODAY WITH THIS FEATURE TRACKING NEWD INTO THE UPPER OH VALLEY BY LATE TONIGHT/EARLY WED.

…TN VALLEY SWD INTO THE LOWER MS VALLEY AND CNTRL/ERN GULF STATES THIS AFTERNOON THROUGH TONIGHT…

MATURE-TO-DECAYING MCS ONGOING FROM NERN GA TO THE CNTRL FL PNHDL SHOULD CONTINUE TO WEAKEN THROUGH THE REMAINDER OF THE MORNING WHILE PROGRESSING EWD. IN ITS WAKE…STRENGTHENING SWLY LOW-LEVEL FLOW WILL ENHANCE THE POLEWARD TRANSPORT OF A VERY MOIST AIR MASS –CURRENTLY RESIDING ALONG AN OUTFLOW BOUNDARY OVER SRN LA– THROUGH MS/AL/SRN TN WITH DEWPOINTS RISING BACK THROUGH THE 60S. THIS PROCESS WILL OCCUR BENEATH A RESIDUAL PLUME OF MODESTLY STEEP MIDLEVEL LAPSE RATES…PROMOTING A MODERATELY UNSTABLE ENVIRONMENT BY AFTERNOON WITH MLCAPE OF 2000-2500 J/KG.

FORCING FOR ASCENT…ASSOCIATED WITH THE EXIT REGION OF THE MIDLEVEL JET STREAK PROGRESSING THROUGH THE ARKLATEX INTO LOWER MS VALLEY…WILL COMBINE WITH LOW-LEVEL UPLIFT ALONG THE OUTFLOW BOUNDARY MOVING NWD INTO SRN PARTS OF MS/AL AND THE COLD FRONT EDGING EWD/SEWD INTO WRN PARTS OF TN/MS TO FOSTER SCATTERED TO NUMEROUS TSTMS THIS AFTERNOON. WHILE LOW-LEVEL SHEAR IS EXPECTED TO BE WEAKER THAN YESTERDAY…THE COMBINATION OF THE MODERATE INSTABILITY AND 50-70 KT OF DEEP-LAYER SHEAR WILL BE VERY FAVORABLE FOR LONG-LIVED SUPERCELLS CAPABLE OF VERY LARGE HAIL AND TORNADOES…A FEW OF WHICH COULD BE STRONG ACROSS PARTS OF MS AND AL THIS AFTERNOON INTO TONIGHT.

BY LATER THIS EVENING INTO THE OVERNIGHT HOURS…STORMS WILL LIKELY COALESCE INTO A NE-SW-ORIENTED MCS WITH EMBEDDED SUPERCELL AND BOWING STRUCTURES WITH A CONTINUED RISK FOR MAINLY DAMAGING WINDS AND A FEW TORNADOES ACROSS PARTS OF THE SRN APPALACHIANS TO CNTRL AND ERN GULF COAST.

…CAROLINAS THIS AFTERNOON INTO TONIGHT…

A BELT OF 25-30 KT SLY FLOW AT 850 MB WILL BE MAINTAINED TODAY E OF THE CNTRL/SRN APPALACHIANS WHICH WILL PROMOTE THE POLEWARD FLUX OF 65-70 F BOUNDARY-LAYER DEWPOINTS THROUGH THE WARM SECTOR. AND WHILE MIDLEVEL LAPSE RATES WILL NOT BE PARTICULARLY STEEP…THE INCREASING MOISTURE COUPLED WITH DAYTIME HEATING WILL YIELD AFTERNOON MLCAPE OF 1000-1500 J/KG.

LOW-LEVEL CONVERGENCE/UPLIFT ALONG THE NWD-MOVING WEDGE FRONT AND/OR RESIDUAL CONVECTIVE OUTFLOW BOUNDARIES ASSOCIATED WITH A DECAYING MCS MOVING INTO THE AREA FROM THE SW IS EXPECTED TO FOSTER ISOLATED TO SCATTERED TSTMS BY AFTERNOON WITHIN A KINEMATIC ENVIRONMENT FEATURING A VERTICALLY VEERING WIND PROFILE WITH 30-40 KT OF DEEP-LAYER SHEAR. ORGANIZED STORM MODES INCLUDING SUPERCELLS ARE POSSIBLE WITH THE PRIMARY HAZARDS BEING LARGE HAIL AND DAMAGING WINDS. THE GREATEST TORNADO THREAT MAY MATERIALIZE ACROSS CNTRL NC THIS AFTERNOON INVOF OF THE WEDGE FRONT WHERE LOW-LEVEL SHEAR IS ENHANCED.

…OH VALLEY INTO GREAT LAKES THIS AFTERNOON INTO TONIGHT…

FORCING FOR ASCENT/DCVA ATTENDANT TO A VORTICITY MAXIMUM LIFTING NWD FROM THE MID SOUTH/LOWER OH VALLEY WILL AUGMENT LOW-LEVEL CONVERGENCE ALONG PRE-EXISTING OUTFLOW BOUNDARIES AND/OR CONFLUENCE ZONES TO PROMOTE ISOLATED TO WIDELY SCATTERED LOW-TOPPED TSTMS AMIDST A STEEP-LAPSE-RATE ENVIRONMENT WITH AFTERNOON MLCAPE OF 500-1500 J/KG. FORECAST WIND PROFILES INDICATE GENERALLY STRONG DEEP-LAYER SPEED SHEAR WITH THE EXCEPTION BEING ALONG THE WARM FRONT WHERE LOW-LEVEL SHEAR IS ENHANCED. AS SUCH CONVECTIVE MAY BE A MIXTURE OF LINE SEGMENTS AND SUPERCELLS CAPABLE OF PRIMARILY LARGE HAIL. LOCALLY DAMAGING WINDS WILL BE POSSIBLE WITH THE LINEAR STRUCTURES WHILE A TORNADO CANNOT BE RULED OUT WITH SUPERCELLS INTERACTING WITH THE WARM FRONT.

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