SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0235 PM CDT SUN MAY 27 2012 VALID 272000Z - 281200Z ...THERE IS A MDT RISK OF SVR TSTMS FROM N CNTRL KS INTO SWRN MN... ...THERE IS A SLGT RISK OF SVR TSTMS FROM NWRN OK INTO MN AND WRN UPPER MI... ...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF NERN OH AND NWRN PA... NO MAJOR CHANGES WERE MADE TO THE PREVIOUS OUTLOOK. - SHUNTED LOW END TORNADO PROBABILITIES ASSOCIATED WITH BERYL FARTHER S IN LINE WITH EXPECTED PATH OF DEEPER CONVECTION AND CENTER TRACK. - REMOVED A SMALL PORTION OF NERN OH AND NWRN PA FROM THE SLIGHT AS STORMS HAVE PASSED THROUGH THE AREA LEAVING BEHIND A STABLE AIR MASS. ..JEWELL.. 05/27/2012 .PREV DISCUSSION... /ISSUED 1137 AM CDT SUN MAY 27 2012/ ...CNTRL PLAINS ACROSS UPPER MS VALLEY... PREVIOUS FORECAST REASONING AND OUTLOOKS REMAIN ON TRACK. STRONG UPPER SUPPORT FOR DEEP-LAYER ASCENT WILL ACCOMPANY A POTENT SHORT WAVE TROUGH NOW CROSSING THE FOUR CORNERS PER WATER VAPOR IMAGERY AND SHORT TERM MODEL/OBJECTIVE DATA LOOPS. WHILE AIRMASS ACROSS MUCH OF THE PLAINS REMAINS SUBSTANTIALLY CAPPED DUE TO VERY WARM EML PLUME THAT HAS HINDERED MORE WIDESPREAD TSTM DEVELOPMENT IN RECENT DAYS...LATE TODAY SHOULD BE DIFFERENT THAN PREVIOUS DAYS AS FAR AS STORM INITIATION AND COVERAGE. UPPER FORCING WITH THE SHORT WAVE TROUGH WILL ACT TO 1) FORCE LARGE SCALE ASCENT THAT IN TURN WILL COOL MID LEVELS AND SUBSEQUENTLY WEAKEN INHIBITION...AND 2) ENHANCE LOW LEVEL CONVERGENCE SUBSTANTIALLY ALONG AN ADVANCING SURFACE COLD FRONT AND NEAR LOW PRESSURE AREAS ALONG THE FRONT. WHEN COMBINED WITH STRONG SURFACE HEATING ACROSS MUCH OF THE PLAINS INTO SRN MN...CONFIDENCE IS RELATIVELY HIGH THAT TSTMS WILL INITIATE DURING THE 21-00Z TIME FRAME. FROM N-CNTRL KS NNEWD THROUGH S-CNTRL/ERN AND INTO SWRN MN...THE PRESENCE OF 35-45 KT OF DEEP-LAYER SHEAR WILL BE SUPPORTIVE OF SUPERCELLS AS AN INITIAL STORM MODE. THE CHANCE FOR LARGE HAIL WILL BE GREATEST DURING THIS PHASE OF DEVELOPMENT. STORM SCALE GUIDANCE DEPICTS THE GREATER CHANCE FOR DAMAGING DOWNBURST WINDS TO OCCUR ACROSS THE SRN AREA OF THE MDT RISK...NEB/KS...WHERE PRE-STORM DEEP MIXING AND HEATING OF THE BOUNDARY LAYER SHOULD SUPPORT LARGE SURFACE-TD SPREADS. EXPECT THAT STORMS WILL COALESCENCE INTO MCS/QLCS ACROSS THE MID-MO VALLEY DURING THE EVENING WITH SHEAR VECTORS ORIENTED NEARLY PARALLEL TO THE INITIATING BOUNDARY RESULTING IN THIS EVOLUTION. SOME TORNADO POTENTIAL WILL EXIST ALONG THE ENTIRE ZONE OF STORM INITIATION GIVEN MAGNITUDE OF VERTICAL SHEAR TO SUPPORT SUPERCELLS. POCKETS OF GREATER ENHANCED LOW LEVEL SHEAR AND RELATIVELY LOWER LCLS NEAR THE LOW CENTERS AND ALONG THE WARM FRONT INTO MN COULD RESULT IN A TORNADO OR TWO. A POSSIBLE FACTOR LIMITING MORE SUBSTANTIAL TORNADO THREAT IS LATE DAY TIMING OF STORM INITIATION...A WELL MIXED BOUNDARY LAYER OVER MUCH OF THE REGION...AND THE TREND TOWARD FORCED/LINEAR INITIATION ALONG THE COLD FRONT. ...SRN ATLC COAST -- STS BERYL... POTENTIAL EXISTS FOR ISOLATED/TRANSIENT SUPERCELLS TO FORM OVER ATLC AND MOVE ASHORE...AND BRIEF TORNADO CANNOT BE RULED OUT. LIMITING FACTORS INCLUDE LACK OF MORE ROBUST BUOYANCY...AND SPARSE COVERAGE/AMOUNT OF DEEPEST CONVECTION. CENTER OF STS BERYL IS EXPECTED TO MOVE INLAND NERN FL AFTER 00Z...PER LATEST NHC TRACK GUIDANCE. GIVEN FCST OF LITTLE CHANGE IN MAGNITUDE/INTENSITY OF OUTER WIND RADII BEFORE LANDFALL...SIZE/STRENGTH OF WIND ENVELOPE CONTRIBUTING TO FAVORABLE LOW-LEVEL SHEAR FOR SUPERCELLS SHOULD NOT CHANGE MUCH FROM PRESENT ESTIMATES. THIS LEAVES OUTER RIM OF FAVORABLE SHEAR N THROUGH SE OF CENTER AT ABOUT 150 NM...SUPPORTED BY CLX RADAR VWP. THIS SECTOR OF CIRCULATION ENVELOPE...CONTAINING 0-1 KM AGL SRH IN 200-400 J/KG RANGE...GRADUALLY WILL SHIFT INLAND EXTREME SRN SC AND GA THROUGH REMAINDER PERIOD...AMIDST ADVECTION OF HIGHER SFC THETAE FROM ATLC. SMALL STABLE LAYERS ALOFT...SUCH AS OBSERVED IN 12Z CHS RAOB...MAY CONTINUE TO LIMIT BUOYANCY AND INTENSITY OF CONVECTION...ALTHOUGH CAPE SHOULD INCREASE SOMEWHAT WITH INFUSION OF MORE PURELY MARITIME/TROPICAL BOUNDARY-LAYER AIR. MRGL TORNADO PROBABILITIES HAVE BEEN EXPANDED INLAND SOMEWHAT TO ACCOUNT FOR JUXTAPOSITION OF TROPICAL MOISTURE AND FAVORABLE SHEAR...THOUGH INLAND EXPANSION OF THIS REGIME WILL OCCUR MAINLY OVERNIGHT WITHOUT BENEFIT OF DIABATIC SFC HEATING TO AID CAPE. REF NHC ADVISORIES -- E.G. WMO HEADER WTNT32 KNHC -- FOR LATEST TRACK/INTENSITY/WATCH/WARNING GUIDANCE REGARDING THIS CYCLONE. ...MI TO NORTHEAST... A STALLED FRONT ACROSS SRN NJ...THE PA/MD BORDER INTO OH SHOULD SERVE AS A FOCUS FOR CONVECTIVE INITIATION THIS AFTERNOON AS A SERIES OF SUBTLE UPPER WAVES GLANCE THE REGION. MINIMAL CONVECTIVE INHIBITION HAS ERODED WITH MORNING HEATING AND MODERATE INSTABILITY SHOULD FUEL A FEW STRONGER CELLS CAPABLE OF DMGG WIND AND HAIL. A WEAK NW FLOW REGIME SHOULD LIMIT STORM ORGANIZATION/PERSISTENCE BUT PW VALUES OF 150 TO 200 PCT OF NORMAL AND SLOW STORM MOTIONS MAY CONTRIBUTE TO HEAVY RAINFALL. ACROSS THE LOWER PENINSULA OF MI...MODEST MID-UPPER LEVEL WNWLY FLOW ASSOCIATED WITH LOW AMPLITUDE SHORT WAVE TROUGHS CRESTING THE UPPER MID/RIDGE AXIS MAY CONTINUE TO SUPPORT SEWD PROPAGATION OF SMALL MCS/S REMOVED FROM GREATER SURFACE-BASED INSTABILITY. A MOIST AND WEAKLY UNSTABLE AIR MASS IN ADDITION TO UPPER SUPPORT WILL CONTINUE TO SUPPORT THE MCS/S TRACKING TO THE WRN NY/PA BORDER IN THE 18-19Z TIME FRAME. WITH ADEQUATE DOWNSTREAM DESTABILIZATION...A THREAT OF FOR DMGG WINDS MAY EVOLVE IN AREAS WHERE BOUNDARY LAYER HAS HAD TIME TO WARM. THUS...A SMALL SLGT RISK HAS BEEN ISSUED WITH THIS OTLK FROM NERN OH TO EXTREME WRN NY.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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