SPC AC 151955 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0255 PM CDT THU AUG 15 2013 VALID 152000Z - 161200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CENTRAL AND SOUTHERN PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS OVER SOUTHEAST GA AND NORTHEAST FL... ...CENTRAL AND SRN PLAINS... OBJECTIVE ANALYSES INDICATED THE ENVIRONMENT ACROSS MORE OF CENTRAL KS INTO CENTRAL OK AND SOUTHWARD INTO THE LOW ROLLING PLAINS OF NORTHWEST TX HAS BECOME MODERATELY UNSTABLE THIS AFTERNOON. SATELLITE AND RADAR IMAGERY SHOWED TSTMS DEVELOPING WITHIN A CORRIDOR OF LOW LEVEL CONVERGENCE EXTENDING FROM S-SE OF KABI NNEWD THROUGH WRN NORTH TX...WEST CENTRAL OK INTO CENTRAL KS. THE COMBINATION OF THE INSTABILITY AND EFFECTIVE BULK SHEAR OF 25-35 KT SUGGESTS THE SEVERE WEATHER THREAT HAS EXPANDED EWD SOME AND THUS RESULTS IN THE EWD SPATIAL CHANGE TO THE SLIGHT RISK AREA. ADDITIONAL STORMS SHOULD CONTINUE TO DEVELOP IN VICINITY OF A SWD MOVING OUTFLOW BOUNDARY IN NWRN...CENTRAL AND NORTH CENTRAL KS...WITH THE LATTER AREA HAVING STORMS FORM AT THE MERGER OF TWO OUTFLOW BOUNDARIES. WHILE A SLIGHT RISK REMAINS INTO PART OF SRN NEB...THE HIGHER SEVERE WIND/HAIL PROBABILITIES /I.E. 30 PERCENT RISK LEVEL/ ARE NOT EXPECTED TO EXTEND TO THE NEB BORDER WITH THE NRN EXTENT NOW AS FAR NORTH AS THE NWRN-NORTH CENTRAL KS OUTFLOW BOUNDARY. ...SRN GA/NRN FL... TSTM/SVR WEATHER THREAT FORECAST REMAINS ON TRACK ACROSS THE PORTION OF THE SOUTHEAST STATES...WITH OBJECTIVE ANALYSES INDICATING THE ENVIRONMENT HAS BECOME MODERATELY UNSTABLE. FOR ADDITIONAL MESOSCALE DETAILS FOR THIS REGION...PLEASE REFER TO SPC MESOSCALE DISCUSSION 1721. ..PETERS.. 08/15/2013 .PREV DISCUSSION... /ISSUED 1138 AM CDT THU AUG 15 2013/ CORRECTED TO REMOVE EXTRA GENL TSTM LINE OVER MAINE. ...WRN TO CNTRL KS SOUTH TO TX/OK PNHDLS AND WRN OK... MID-LEVEL TROUGHING AND STRENGTHENING NNWLY MID-LEVEL FLOW IS FORECAST OVER THE GREAT PLAINS THROUGH TONIGHT DOWNSTREAM FROM MID/UPPER RIDGE AMPLIFICATION ACROSS THE ROCKIES. THIS PROCESS WILL CONTRIBUTE TO A WEAK LEE CYCLONE RIPPLING SSEWD ALONG/NEAR SFC/THERMAL TROUGH AXIS FROM ERN CO TO TX PNHDL BY FRIDAY MORNING. MORNING WATER VAPOR AND VISIBLE SATELLITE LOOPS DEPICT AT LEAST TWO SHORTWAVE TROUGHS THAT WILL ACT TO ENHANCE ASCENT ACROSS KS THROUGH THE AFTERNOON AND INTO THE EVENING. THE FIRST...A MCV ASSOCIATED WITH LOOSELY ORGANIZED OVERNIGHT MCS...WAS MOVING INTO NRN KS LATE THIS MORNING. THE OUTFLOW BOUNDARY FROM THE MCS EXTENDED FROM E-CNTRL KS WWD/NWWD TO NERN CO. NEW ELEVATED CONVECTION WAS OCCURRING AMIDST AN EXPANDING ACCAS FIELD WELL AHEAD OF THE MCV AND OUTFLOW FROM CNTRL KS TO WRN/CNTRL OK. WEAK POST-OUTFLOW CONVECTION WAS PERSISTING OVER NERN CO AND SRN NEB. THE SECOND SHORTWAVE TROUGH WAS EVIDENT ACROSS MT/WY. THIS IMPULSE WILL LIKELY ACT TO REINFORCE OR SUSTAIN DEEP-LAYER ASCENT AND STRENGTHENING SHEAR ACROSS THE PLAINS THROUGH TONIGHT. HEATING/MIXING WILL ELIMINATE WEAK CONVECTIVE INHIBITION ACROSS THE RISK AREA THROUGH THE AFTERNOON WITH SFC-BASED STORMS LIKELY BY LATE AFTERNOON. LOW 60S F BOUNDARY LAYER DEWPOINTS BENEATH 7-8 C/KM MID-LEVEL LAPSE RATES WILL RESULT IN MLCAPE OF 2000-2500 J/KG. DEEP-LAYER VERTICAL SHEAR WILL BE FAVORABLE FOR SUPERCELLS GIVEN 30-50 KT NNWLY FLOW ALOFT AND WEAK SLY/SWLY LOW-LEVEL FLOW. INITIALLY...THE POTENTIAL FOR DISCRETE SUPERCELLS WILL EXIST AND THESE STORMS WILL BE CAPABLE OF PRODUCING VERY LARGE HAIL AND STRONG TO DAMAGING WINDS. HODOGRAPH CURVATURE AND BOUNDARY LAYER RH ARE LIMITED BY LACK OF STRONGER LOW LEVEL FLOW AND MOISTURE RESPECTIVELY AND THESE FACTORS MAY LIMIT TORNADO POTENTIAL. HOWEVER...IF CONVECTION CAN REMAIN AT LEAST SEMI-DISCRETE INTO THE EARLY EVENING...THE POSSIBILITY OF STORM/BOUNDARY INTERACTIONS AND A SLIGHT INCREASE IN LOW LEVEL FLOW COULD ENHANCE THE CHANCE FOR A TORNADO OR TWO. IN ADDITION TO INITIAL RISK FOR DAMAGING SUPERCELL GUSTS...SOME CHANCE EXISTS FOR UPSCALE/MCS ORGANIZATION OVERNIGHT. LATEST STORM SCALE GUIDANCE SUGGESTS THIS POTENTIAL WILL REMAIN QUITE LIMITED AND PROBABLY FOCUSED FROM SRN KS TO NRN OK DURING THE LATE EVENING/OVERNIGHT HOURS. ...NRN FL/SRN GA... A QUASI-STATIONARY FRONT FROM WRN FL PNHDL ACROSS SRN GA HAS BECOME BETTER DEFINED THIS MORNING DUE TO DENSE CLOUD COVER TO THE NORTH AND RESULTANT DIFFERENTIAL HEATING. MLCAPE ALONG AND SOUTH OF THE BOUNDARY HAS ALREADY CLIMBED TO AROUND 2000 J/KG AHEAD OF A CLUSTER OF ROBUST CONVECTION SPREADING ENEWD FROM FL PNHDL/SWRN GA. A WEAK MID-LEVEL IMPULSE ROTATING THROUGH THE BASE OF THE LARGER SCALE TROUGH...AND MODEST 25KT MID-LEVEL FLOW...SHOULD CONTRIBUTE TO STORM ORGANIZATION/PERSISTENCE AND ACT TO ENHANCE LIFT ALONG THE FRONTAL ZONE THROUGH THE AFTERNOON. ADDITIONAL CONVECTION WILL LIKELY INCREASE ALONG SEA BREEZES ACROSS FL. GIVEN CURRENT TRENDS...A CORRIDOR WITH A GREATER DOWNBURST WIND POTENTIAL MAY EVOLVE OVER PORTIONS OF NRN FL AND SRN GA INTO THE AFTERNOON. THUS...TSTM WIND PROBABILITIES HAVE BEEN INCREASED ACROSS THESE AREAS. NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
Posted on: Thu, 15 Aug 2013 20:10:05 +0000
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