Here is the updated spc outlook as of noon. Like I said earlier everything shifted more north! Grrrr. THERE IS A SLGT RISK OF SVR TSTMS OVER FAR S-CNTRL ND INTO ERN SD... ...SUMMARY... ISOLATED SEVERE THUNDERSTORMS CAPABLE OF HAIL AND LOCALLY STRONG WIND GUSTS WILL BE POSSIBLE ACROSS PARTS OF THE GREAT PLAINS THIS AFTERNOON AND EVENING. THE GREATEST RISK FOR A COUPLE OF TORNADOES WILL BE ACROSS EASTERN SOUTH DAKOTA INTO SOUTH-CENTRAL NORTH DAKOTA. ELSEWHERE...A FEW STORMS WITH HAIL MAY OCCUR THIS AFTERNOON OVER PENNSYLVANIA AND ADJACENT STATES. ...SYNOPSIS... A BRIEFLY CLOSED MID TO UPPER-LEVEL LOW OVER WRN SD WILL EVOLVE BACK INTO A NEGATIVELY TILTED WAVE WHILE EJECTING NNEWD INTO S-CNTRL CANADA IN RESPONSE TO THE AMPLIFICATION OF AN UPSTREAM SHORT-WAVE TROUGH OVER THE INTERIOR WEST. BETWEEN THESE TWO SYSTEMS...ONE OR MORE WEAK VORTICITY MAXIMA WILL PROGRESS FROM THE CNTRL ROCKIES INTO CNTRL PLAINS WITHIN THE BASE OF THE LONG-WAVE TROUGH PRESENT OVER THE INTERIOR WEST THROUGH GREAT PLAINS. AT THE SURFACE...AN OCCLUDED CYCLONE OVER WRN SD WILL GRADUALLY FILL WHILE DEVELOPING NNEWD THROUGH CNTRL ND...IN TANDEM WITH THE UPPER SYSTEM. AN ASSOCIATED OCCLUDED/WARM FRONT WILL CONCURRENTLY SHIFT NWD THROUGH THE ERN DAKOTAS AND WRN MN WHILE A PACIFIC FRONT/DRYLINE STALLS FROM ERN SD THROUGH CNTRL NEB...WRN KS INTO THE OK/TX PNHDLS. ELSEWHERE...A WEAK COLD FRONT OVER THE UPPER OH VALLEY INTO LOWER GREAT LAKES WILL SETTLE SLOWLY SEWD INTO THE CNTRL APPALACHIANS/MID ATLANTIC REGION. ...S-CNTRL ND INTO ERN SD THIS AFTERNOON/EVENING... VISIBLE SATELLITE IMAGERY SUGGESTS THAT A CORRIDOR OF STRONGER HEATING SHOULD OCCUR WITHIN THE MID-LEVEL DRY SLOT WRAPPING CYCLONICALLY THROUGH THE ERN SEMI-CIRCLE OF THE UPPER SYSTEM. WHEN COUPLED WITH BOUNDARY-LAYER DEWPOINTS IN THE 50S...EXPECT AT LEAST WEAK DESTABILIZATION /MLCAPE OF AROUND 500 J PER KG/ TO OCCUR ALONG THE NWD-MIGRATING SURFACE OCCLUDED/WARM FRONT. THIS SHOULD FOSTER THE DEVELOPMENT OF A NARROW CONVECTIVE BAND BY AFTERNOON AMIDST A KINEMATIC ENVIRONMENT FEATURING PRONOUNCED VEERING OF WINDS WITH HEIGHT WITH EFFECTIVE SRH VALUES INCREASING TO 150-250+ M2/S2. AS SUCH...A FEW LOW-TOPPED SUPERCELLS ARE POSSIBLE WITH A RISK FOR A COUPLE TORNADOES AND PERHAPS SOME MARGINALLY SEVERE HAIL. ...ERN NEB/WRN IA TO ERN OK/TX PNHDLS AND WRN OK... CONSIDERABLE EARLY-DAY CLOUDINESS /INCLUDING A FEW TSTMS/ IS PRESENT WITHIN THE WARM-CONVEYOR AIR STREAM FROM CNTRL KS TO ERN NEB/WRN IA WHICH WILL LIKELY SLOW THE DESTABILIZATION PROCESS IN THOSE AREAS. HOWEVER...WHERE STRONGER HEATING CAN OCCUR...THE PRESENCE OF BOUNDARY-LAYER DEWPOINTS IN THE MID TO UPPER 50S AND MODESTLY STEEP MID-LEVEL LAPSE RATES WILL YIELD AFTERNOON MLCAPE APPROACHING 1000-1500 J/KG. AS MENTIONED IN THE SYNOPSIS...WEAK VORTICITY MAXIMA EMERGING FROM THE CNTRL ROCKIES WILL OVERSPREAD THE REGION LATER TODAY...WHICH IN CONCERT WITH LOW-LEVEL CONVERGENCE ALONG THE DRYLINE/PACIFIC FRONT AND/OR OUTFLOW BOUNDARIES FROM EARLY-DAY TSTMS SHOULD FOCUS ISOLATED TO WIDELY SCATTERED AFTERNOON STORM DEVELOPMENT. WEAK MID-LEVEL LAPSE RATES AND THE ABOVE-MENTIONED CLOUDS ARE EXPECTED TO TEMPER UPDRAFT VIGOR AND THE POTENTIAL FOR AN ORGANIZED SEVERE WEATHER EPISODE. NONETHELESS...A FEW SEVERE STORMS /INCLUDING MARGINAL SUPERCELL STRUCTURES/ ARE POSSIBLE WITH THE PRIMARY HAZARDS BEING HAIL AND LOCALLY STRONG WIND GUSTS. ...LOWER GREAT LAKES/CNTRL APPALACHIANS THIS AFTERNOON... A MID TO UPPER-LEVEL LOW OVER THE UPPER OH VALLEY/LOWER GREAT LAKES WILL PROGRESS ESEWD WITH THE ASSOCIATED COLD POOL ALOFT OVERSPREADING A PRE-FRONTAL AIR MASS WHICH SHOULD EXPERIENCE ABUNDANT SUNSHINE AND THE DEVELOPMENT OF AT LEAST MODEST INSTABILITY BY AFTERNOON. WHILE THE STRONGEST DEEP-LAYER SHEAR ASSOCIATED WITH A 40-50 KT MID-LEVEL JET STREAK ROUNDING THE BASE OF THE TROUGH WILL REMAIN DISPLACED TO THE SOUTH OF THE GREATER DESTABILIZATION...THE STEEPENING LAPSE RATES MAY SUPPORT SOME HAIL WITH THE STRONGEST STORMS.
Posted on: Tue, 30 Sep 2014 17:32:32 +0000
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