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| Probabilistic Tornado Graphic | |||||||||
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| Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. |
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| Probabilistic Damaging Wind Graphic | |||||||||
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| Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point. |
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| Probabilistic Large Hail Graphic | |||||||||
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| Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point. |
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SPC AC 211956 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0256 PM CDT SAT SEP 21 2013 VALID 212000Z - 221200Z ...NO SVR TSTM AREAS FORECAST... ...SERN STATES... THE ERN LONGWAVE TROUGH AND ATTENDANT COLD FRONT WILL CONTINUE TO SHIFT EWD...ALLOWING THE WRN EXTENT OF THE 2 PERCENT TORNADO PROBABILITY AND GENERAL TSTM AREA TO BE SHIFTED EWD. THE REST OF THE 2 PERCENT TORNADO PROBABILITY FORECAST REMAINS ON TRACK. EARLY AFTERNOON RADAR IMAGERY SHOWED A COUPLE OF N-S ORIENTED LINES OF CONVECTION/EMBEDDED TSTMS WITH SOME WEAK ROTATIONAL COUPLETS. THE DOWNSTREAM ENVIRONMENT IS MARGINALLY UNSTABLE TO SUPPORT FURTHER TSTMS THROUGH THE AFTERNOON...THOUGH WEAK DEEP LAYER AND LOW LEVEL SHEAR PER AREA VADS WILL CONTINUE TO LIMIT THE OVERALL SEVERE WEATHER THREAT. ...DELMARVA INTO SRN NEW ENGLAND... NO CHANGES FOR THIS OUTLOOK AREA. REFER TO THE DISCUSSION ISSUED AT 1128 AM CDT. ..PETERS.. 09/21/2013 .PREV DISCUSSION... /ISSUED 1128 AM CDT SAT SEP 21 2013/ ...DELMARVA INTO SRN NEW ENGLAND... PROGRESSIVE UPPER FLOW PATTERN WILL CONTINUE DURING THE PERIOD AS A STRONG SHORT WAVE TROUGH EXTENDING FROM THE GREAT LAKES ACROSS THE MID-SOUTH AND ARKLATEX REGION MOVES EWD/SEWD THROUGH TONIGHT. WIDESPREAD CLOUDS AND PRECIPITATION ARE OCCURRING IN ADVANCE OF THE UPPER SYSTEM AND ASSOCIATED COLD FRONT WITHIN A VERY MOIST AIR MASS...WITH PW VALUES RANGING FROM 1.5 IN OVER THE LOWER GREAT LAKES TO AOA 2 IN FROM THE TN VALLEY SWD INTO THE WRN/CENTRAL GULF OF MEXICO. 12Z RAOBS ALSO INDICATE WEAK LAPSE RATES WITHIN THIS ENVIRONMENT WHICH IS LIMITING THE MAGNITUDE OF INSTABILITY AND RESULTANT VERTICAL VELOCITY OF CONVECTIVE UPDRAFTS. DYNAMIC FORCING FOR LARGE SCALE ASCENT IS EXPECTED TO BE STRONGEST FROM THE DELMARVA NWD INTO NEW ENGLAND LATER THIS AFTERNOON AND TONIGHT IN ASSOCIATION WITH INCREASING DCVA AND DIVERGENCE ALOFT WITHIN THE EXIT REGION OF THE MERIDIONALLY-ORIENTED UPPER JET. DESPITE WEAK INSTABILITY WITH CAPE AOB 500 J/KG...A FEW LOW-TOPPED CONVECTIVE CLUSTERS/SHORT LINE SEGMENTS MAY DEVELOP ACROSS THIS REGION AS THE FRONT MOVES EWD. CG LIGHTNING IS EXPECTED TO BE LIMITED...HOWEVER...INCREASING SSWLY LOW LEVEL FLOW /40-50 KT AT 850 MB/ SUGGESTS POTENTIAL FOR ISOLATED STRONG WIND GUSTS AT THE SURFACE AS DOWNWARD TRANSFER OF STRONG HORIZONTAL MOMENTUM OCCURS WITHIN CONVECTIVE DOWNDRAFTS. A 5% WIND PROBABILITY HAS BEEN INTRODUCED TO ACCOUNT FOR THIS POSSIBILITY...BUT WEAK INSTABILITY AND RESULTANT LOW THUNDERSTORM PROBABILITY ARE EXPECTED TO LIMIT OVERALL SEVERE THREAT. ...SERN STATES INTO ERN PARTS OF SC/NC... STRONGEST CONVECTION IS CURRENTLY OVER THE CENTRAL GULF OF MEXICO AND IMMEDIATE COASTAL SECTIONS LA/MS/AL AND NWRN FL. RADAR HAS INDICATED WEAK ROTATIONAL COUPLETS IN ISOLATED CONVECTIVE CELLS FARTHER INLAND FROM SERN LA INTO NRN AL EARLIER IN THE MORNING IN ASSOCIATION WITH 30-40 KT SWLY LOW LEVEL WINDS AND MARGINALLY FAVORABLE LOW LEVEL SHEAR. A THREAT FOR A BRIEF TORNADO OR TWO MAY PERSIST INTO THE AFTERNOON OVER PARTS OF AL/GA AND NWRN FL THIS AFTERNOON...AND THEN REDEVELOP TONIGHT FARTHER TO THE NORTHEAST OVER THE COASTAL PARTS OF THE CAROLINAS AS THE ENVIRONMENT BECOMES MARGINALLY UNSTABLE AND STRONGER LOW LEVEL FLOW/SHEAR OVERSPREAD THE REGION. CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z |
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