SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0301 PM CDT FRI JUN 01 2012 VALID 012000Z - 021200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF SRN PA...FAR ERN WV...MD AND NRN VA... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS WRN AND SRN PA..AND THE MID AND SRN ATLANTIC STATES... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS NERN NM TO SWRN KS AND WRN OK... ...VA/MD/SRN AND SERN PA... THE 1630Z SCENARIO INDICATING THE POTENTIAL FOR TORNADOES FORMING ALONG A QLCS AS THE COLD FRONT ADVANCES EWD THIS FORECAST PERIOD REMAINS ON TRACK. DISCRETE STORMS HAVE ALSO FORMED WELL IN ADVANCE OF THE COLD FRONT WITHIN THE WARM SECTOR...BOUNDED ON THE N/NE BY A WARM FRONT MOVING SLOWLY NNEWD. EFFECTIVE SRH OF 200-300 M2/S2 FROM NRN VA INTO NRN MD/SERN PA AND NRN DE WILL CONTINUE TO PROMOTE A POTENTIAL FOR TORNADIC SUPERCELL STRUCTURES AS HAVE BEEN DETECTED THUS FAR ACROSS PARTS OF NRN VA INTO NRN MD. GIVEN THESE FACTORS...A SIGNIFICANT TORNADO PROBABILITY AREA HAS BEEN ADDED. ...NERN NM TO SWRN KS AND WRN OK... MODELS SUGGEST AN INCREASE IN TSTM DEVELOPMENT ACROSS THIS REGION THROUGH THE AFTERNOON/EARLY EVENING WITH AN ATTENDANT THREAT FOR HAIL...SOME VERY LARGE...AND DAMAGING WINDS. FURTHER DETAILS ARE AVAILABLE IN MESOSCALE DISCUSSION 1006...AND 20Z OUTLOOK HAS EXPANDED THE SLIGHT RISK AND SEVERE PROBABILITIES BOTH TO THE W AND THE E/NE. ...CENTRAL FL PENINSULA... DESPITE RELATIVELY WEAK INSTABILITY...ENHANCED LOW LEVEL SHEAR ALONG A WSW-ENE ORIENTED BOUNDARY LOCATED JUST N OF LAKE OKEECHOBEE AND LOW LEVEL CONVERGENCE SUGGEST AN ADDITIONAL THREAT FOR A FEW ROTATING UPDRAFTS WITH AN ATTENDANT ISOLATED TORNADO THREAT. THUS...THIS OUTLOOK HAS ADDED A 2 PERCENT TORNADO THREAT. ..PETERS.. 06/01/2012 .PREV DISCUSSION... /ISSUED 1130 AM CDT FRI JUN 01 2012/ ...MID-ATLANTIC/UPPER OH VALLEY/CAROLINAS... THE LATEST WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL TROUGH EXTENDING SWD ACROSS THE OH AND TN VALLEYS. THIS FEATURE WILL BECOME NEGATIVELY TILTED TODAY MOVING EWD INTO THE CNTRL APPALACHIAN MTNS. A BAND OF WELL-FOCUSED LARGE-SCALE ASCENT IS LOCATED TO THE EAST OF THE TROUGH WHICH IS PROVIDING SUPPORT FOR A LINE OF THUNDERSTORMS EXTENDING SWD FROM ERN OH INTO FAR ERN KY. THIS LINE WILL MOVE EWD INTO A WEAKLY UNSTABLE AIRMASS BUT WILL ALSO GAIN ACCESS TO INCREASING LOW-LEVEL MOISTURE AND SLIGHTLY STRONGER INSTABILITY THIS AFTERNOON. FOR THIS REASON...THE LINE IS EXPECTED TO SLOWLY RAMP UP IN INTENSITY WITH A WIND DAMAGE THREAT GRADUALLY DEVELOPING. FURTHER TO THE EAST ACROSS ERN NC...ERN VA AND MD...MESOANALYSIS CURRENTLY SHOWS A CORRIDOR OF MODERATE INSTABILITY WHERE MLCAPE IS ESTIMATED IN THE 1500 TO 2500 J/KG RANGE AND SFC DEWPOINTS ARE APPROACHING 70 F. THUNDERSTORMS ARE EXPECTED TO INITIATE ALONG THE INSTABILITY AXIS THIS AFTERNOON WITH STORMS SPREADING NEWD ACROSS THE MID-ATLANTIC LATE THIS AFTERNOON INTO EARLY THIS EVENING. FORECAST SOUNDINGS ACROSS THE WARM SECTOR LATE THIS AFTERNOON SHOW 0-6 KM SHEAR VALUES IN THE 35 TO 40 KT RANGE WITH 0-3 KM STORM RELATIVE HELICITIES AROUND 250 M2/S2 SUGGESTING THE ENVIRONMENT WILL SUPPORT ROTATING STORMS AND TORNADOES. A TORNADO THREAT WILL LIKELY DEVELOP AS THE STORMS INTERACT WITH A WARM FRONT WHICH IS FORECAST TO BE FROM SCNTRL PA EXTENDING SSEWD ACROSS NRN VA AND MD AS THE LINE APPROACHES FROM THE WEST. THE TORNADO THREAT SHOULD INCREASE ACROSS PA AND MD AS THE STRONGEST BAND OF LARGE-SCALE ASCENT APPROACHES LATER THIS AFTERNOON. A COUPLING OF THE LOW AND MID-LEVEL JETS IS ALSO FORECAST TO OCCUR ACROSS NRN VA...MD AND PA WHICH MAY ALSO HELP TO ENHANCE THE QLCS TORNADO THREAT. HAVE ADDED A MODERATE RISK IN THE WASHINGTON DC METRO...BALTIMORE AREAS WHERE THE TORNADO THREAT IS EXPECTED TO BE THE GREATEST AND WHERE AN ISOLATED STRONG TORNADO CAN NOT BE RULED OUT. ANY ROTATING STORMS SHOULD ALSO BE CAPABLE OF PRODUCING WIND DAMAGE. AS THE STRONGER LARGE-SCALE ASCENT MOVES ACROSS THE MID-ATLANTIC EARLY THIS EVENING...A WELL-ORGANIZED LINEAR MCS IS EXPECTED TO BECOME THE DOMINANT CONVECTIVE FEATURE WITH AN ENHANCED WIND DAMAGE THREAT PRESENT ACROSS A LARGE AREA OF THE MID-ATLANTIC. FURTHER SOUTH ACROSS THE CAROLINAS...LARGE-SCALE ASCENT WILL BE WEAKER THAN IN AREAS TO THE NORTH. HOWEVER...MESOANALYSIS ALREADY SHOWS MODERATE INSTABILITY IN PLACE AND MODEL FORECASTS DO DEVELOP A LINE OF THUNDERSTORMS ALONG THE INSTABILITY AXIS THIS AFTERNOON. FORECAST SOUNDINGS LATE THIS AFTERNOON IN THE ERN CAROLINAS SHOW 0-6 KM SHEAR OF 30 TO 35 KT SUGGESTING THE ENVIRONMENT WILL SUPPORT SEVERE STORMS. AS LOW-LEVEL LAPSE RATES BECOME STEEP THIS AFTERNOON...WIND DAMAGE WILL BE POSSIBLE WITH A LINE OF STORMS FORMING JUST AHEAD OF A COLD FRONT APPROACHING THE REGION FROM THE NORTHWEST. ...SRN GA/NRN FL... REMNANT MCV FROM OVERNIGHT CONVECTION IS SHEARING NEWD AT ROUGHLY 25KT ACROSS SERN AL INTO SWRN GA. IT APPEARS DIURNAL HEATING IS NOW CONTRIBUTING GREATLY TO THE RECENT INCREASE IN TSTM ACTIVITY ALONG LEADING EDGE OF DEBRIS CANOPY AND CONVECTIVE OUTFLOW. GIVEN THE MODEST DEEP LAYER SHEAR AND THE EXPECTED GRADUAL INCREASE IN CONVECTION AHEAD OF THIS FEATURE A SLIGHT RISK WILL BE ADDED TO THIS REGION TO ACCOUNT FOR ISOLATED DAMAGING WINDS AND PERHAPS SOME HAIL. CURRENT SPEED OF THIS FEATURE SUGGESTS THE BACK EDGE OF FORCING WITH MCV WILL PROGRESS INTO SERN GA BY 21Z. ...SWRN KS/TX AND OK PANHANDLES... NORTHWEST FLOW WILL BE IN PLACE ACROSS THE SRN PLAINS TODAY WITH SEVERAL SUBTLE IMPULSES MOVING SEWD ACROSS THE REGION. MESOANALYSIS ALREADY SHOWS AN AXIS OF MODERATE INSTABILITY IN PLACE ACROSS ERN NM. AS THE INSTABILITY AXIS SHIFTS EWD INTO WEST TX THIS AFTERNOON...STRONG INSTABILITY SHOULD DEVELOP AS THE CAPPING INVERSION WEAKENS. THIS SHOULD ALLOW FOR SCATTERED THUNDERSTORM DEVELOPMENT ACROSS THE TX PANHANDLE WITH THIS CONVECTION GRADUALLY MOVING SEWD INTO NORTHWEST TX EARLY THIS EVENING. FORECAST SOUNDINGS AT AMARILLO AT 02/00Z SHOW 0-6 KM SHEAR IN THE 40 TO 50 KT RANGE WITH MID-LEVEL LAPSE RATES APPROACHING 8.0 C/KM. THIS SHOULD SUPPORT A SUPERCELL AND LARGE HAIL THREAT. HOWEVER...LARGE TEMP-DEWPOINT SPREADS MAY ALSO HELP ENHANCE DOWNDRAFT SPEEDS SUGGESTING A WIND DAMAGE THREAT WILL ALSO EXIST ESPECIALLY IF THE STORMS CAN CONGEAL INTO A LINE EARLY THIS EVENING.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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