Categorical Graphic
Probabilistic Tornado Graphic
Probabilistic Damaging Wind Graphic
Probabilistic Large Hail Graphic

   SPC AC 230556
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1256 AM CDT WED APR 23 2008
   
   VALID 231200Z - 241200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE SRN PLAINS
   NWD THROUGH THE CENTRAL/NRN HIGH PLAINS...
   
   ...SYNOPSIS...
   UPPER FLOW PATTERN IS EXPECTED TO BECOME MORE AMPLIFIED OVER THE
   LOWER 48 STATES TODAY AS A DEEP TROUGH MOVES INLAND TO THE WRN U.S.
   AND A DOWNSTREAM RIDGE SHIFTS EWD EXTENDING FROM THE CENTRAL GULF
   COAST STATES TO THE UPPER OH VALLEY/CENTRAL APPALACHIANS BY 12Z
   THURSDAY.  SEVERAL MID LEVEL SHORT WAVE TROUGHS ATTENDANT TO THE WRN
   LONGWAVE TROUGH AND EMBEDDED WITHIN SRN STREAM JET ARE FORECAST TO
   TRANSLATE INTO THE PLAINS...SUPPORTING WIDESPREAD CONVECTIVE
   DEVELOPMENT THIS FORECAST PERIOD.  IN THE LOW LEVELS...SURFACE
   CYCLOGENESIS IS EXPECTED OVER ERN WY THIS AFTERNOON WITH A LEE
   TROUGH/DRY LINE EXTENDING SWD THROUGH THE HIGH PLAINS IN RESPONSE TO
   APPROACHING WRN TROUGH.  A SURFACE BOUNDARY IS EXPECTED TO STALL
   EARLY IN THE PERIOD FROM SD INTO CENTRAL MN...AND THEN RETREAT NWD
   INTO ND/NRN MN THIS EVENING IN RESPONSE TO STRENGTHENING LOW LEVEL
   WINDS AS WY LOW/MID LEVEL TROUGH TRACK NEWD.  FARTHER S...A WARM
   FRONT THIS MORNING RESIDING FROM THE TX PANHANDLE INTO OK SHOULD
   SPREAD NWD...BUT BECOME DIFFUSE AS A BROAD LLJ DEVELOPS ACROSS THE
   PLAINS ADVECTING MOISTURE NWD THROUGH THE WARM SECTOR..
   
   IN THE NORTHEAST...AN UPPER TROUGH...CURRENTLY LOCATED OVER THE
   UPPER GREAT LAKES/NRN ONTARIO...WILL TRACK EWD BREAKING DOWN THE NRN
   EXTENT OF THE ERN RIDGE OVER QUEBEC INTO THE LOWER GREAT LAKES AND
   NEW ENGLAND.  A COLD FRONT ATTENDANT TO THIS SYSTEM WILL MOVE SEWD
   THROUGH THE LOWER GREAT LAKES REGION...REACHING ERN ME TO NRN VA BY
   12Z THURSDAY.
   
   ...SRN PLAINS...
   A LEAD SRN STREAM SHORT WAVE TROUGH/SPEED MAX SHOULD BE LOCATED OVER
   FAR W TX AT 12Z TODAY AND MOVE EWD INTO W TX BY 18Z AND REACH
   OK/ARKLATEX REGION TOWARD 24/00Z...WITH A SECOND IMPULSE...
   CURRENTLY APPROACHING SRN CA/NRN BAJA...REACHING W TX REGION BY LATE
   THIS AFTERNOON.  A MOIST/MODERATELY UNSTABLE AIR MASS CURRENTLY
   EXISTS ACROSS MUCH OF THE SRN PLAINS.  ASCENT AHEAD OF THE LEAD SRN
   STREAM IMPULSE SHOULD BE AIDING IN ONGOING TSTMS AT 12Z TODAY ACROSS
   PARTS OF W TX INTO THE TX PANHANDLE/WRN OK.  DEGREE OF INSTABILITY
   AND 40-50 KT EFFECTIVE BULK SHEAR IN THIS REGION WILL RESULT IN A
   HAIL THREAT WITH THIS EARLY ACTIVITY.  AS THIS LEAD SYSTEM
   TRANSLATES EWD INTO THE SRN PLAINS...ADDITIONAL TSTM DEVELOPMENT IS
   LIKELY TO SPREAD ACROSS MUCH OF OK AND N TX.  STEEP LAPSE RATES WILL
   MAINTAIN A MODERATELY UNSTABLE AIR MASS OVER THE SRN PLAINS WITH
   30-40 KT OF EFFECTIVE SHEAR SUPPORTING A THREAT FOR HAIL AND
   DAMAGING WIND GUSTS.
   
   ALTHOUGH SOME UNCERTAINTY EXISTS WITH DEGREE TO WHICH BOUNDARY LAYER
   CAN DESTABILIZE ACROSS W/NW TX IN WAKE OF MORNING TSTMS... ASCENT
   ATTENDANT TO SRN CA/NRN BAJA TROUGH REACHING THIS REGION BY LATE
   AFTERNOON WILL MAINTAIN HEIGHT FALLS WITH NEW TSTM DEVELOPMENT
   POSSIBLE.  50 KT WSWLY MID LEVEL WINDS ACROSS THE SRN PLAINS WILL
   SUSTAIN STRONG EFFECTIVE BULK SHEAR FOR SUPERCELL STRUCTURES. 
   PRESENT INDICATIONS SUGGEST THIS LATE AFTERNOON CONVECTIVE
   INITIATION SHOULD OCCUR ACROSS NW TX BETWEEN THE SRN TX PANHANDLE TO
   EAST OF MAF TO ABI.  GIVEN DEGREE OF INSTABILITY/DEEP LAYER
   SHEAR...HAIL...SOME VERY LARGE HAIL...AND TORNADOES WILL BE
   POSSIBLE.  THIS ACTIVITY SHOULD THEN DEVELOP ENEWD ACROSS N TX/SRN
   OK AS THIS LATTER SHORT WAVE TROUGH MOVES INTO THE SRN PLAINS WITH
   AN ATTENDANT THREAT FOR HAIL/DAMAGING WINDS.
   
   IF THE MORNING ACTIVITY IS NOT AS EXTENSIVE IN COVERAGE AS CURRENTLY
   EXPECTED...THEN MUCH STRONGER INSTABILITY WILL BE POSSIBLE ACROSS
   PARTS OF THE SRN PLAINS WITH THE POTENTIAL FOR AN UPGRADE TO A
   MODERATE RISK.
   
   ...CENTRAL AND NRN PLAINS...
   A SHORT WAVE TROUGH...CURRENTLY MOVING INLAND OVER NRN CA PER WATER
   VAPOR IMAGERY...IS FORECAST TO TRACK NEWD WITHIN BAND OF STRONG SWLY
   MID-UPPER LEVEL FLOW REACHING WY BY 24/00Z AND THEN INTO THE NRN
   PLAINS TONIGHT.  STEEP MID LEVEL LAPSE RATES /8-9 C/KM/ WILL SPREAD
   EWD ACROSS THE CENTRAL/NRN HIGH PLAINS ATOP WRN EXTENT OF MOISTURE
   RETURN...RESULTING IN A NARROW CORRIDOR OF MODERATE INSTABILITY
   /MLCAPE 1000-1500 J/KG/.  THIS INSTABILITY WILL EXTEND ALONG AND E
   OF DRY LINE FROM ERN WY/SWRN SD SURFACE LOW SWD THROUGH ERN CO/WRN
   KS TO SRN HIGH PLAINS.  WEAK HEIGHT FALLS ACROSS THIS REGION DURING
   THE AFTERNOON COMBINED WITH DIFFLUENT AND DIVERGENT UPPER FLOW IS
   EXPECTED TO AID THE DEVELOPMENT OF SCATTERED TSTMS.  A STRONGLY
   SHEARED ENVIRONMENT AND MODERATE INSTABILITY WILL SUPPORT ISOLATED
   SUPERCELLS CAPABLE OF PRODUCING VERY LARGE HAIL/LOCALLY DAMAGING
   WIND GUSTS AND...PERHAPS...BRIEF TORNADOES.
   
   STRENGTHENING SLY LLJ OVER NEB TO ERN DAKOTAS/MN TONIGHT WILL
   SUPPORT INCREASING LOW LEVEL WAA AND THE LIKELIHOOD FOR AFTERNOON
   ACTIVITY TO DEVELOP AND EXPAND NEWD ACROSS THE DAKOTAS TO MN AFTER
   DARK.  ALTHOUGH BOUNDARY LAYER WILL TEND TO STABILIZE WITH LOSS OF
   DAY TIME HEATING...ELEVATED INSTABILITY AND MODEST EFFECTIVE BULK
   SHEAR SHOULD SUPPORT A THREAT FOR ISOLATED HAIL AS STORMS SPREAD
   NEWD OVERNIGHT.
   
   ...ARKLATEX REGION NWD TO IA...
   SURFACE HEATING WITHIN A MOIST AIR MASS EXTENDING FROM THE LOWER MS
   VALLEY TO LOWER MO VALLEY TODAY SHOULD SUPPORT MODERATE INSTABILITY
   AGAIN TODAY ACROSS THIS REGION.  MODELS SUGGEST TSTMS WILL BE
   POSSIBLE ACROSS THIS REGION ALONG ERN EXTENT OF EML WHERE THE CAP
   SHOULD BE WEAKER.  ENHANCED LOW LEVEL CONVERGENCE IN VICINITY OF
   LEFT OVER OUTFLOW BOUNDARIES FROM TUESDAY CONVECTIVE CLUSTERS MAY
   PROVIDE A FOCUS FOR THIS ACTIVITY.  WEAK TO MODEST DEEP LAYER SHEAR
   SHOULD LIMIT THE SEVERE WEATHER THREAT WITH ISOLATED HAIL/STRONGER
   WIND GUSTS POSSIBLE.
   
   ASCENT ATTENDANT TO LEAD SRN STREAM IMPULSE AND WAA ALONG
   STRENGTHENING LLJ FROM NERN TX TO IA THIS EVENING IS EXPECTED TO
   SUPPORT AN EXTENSIVE ZONE OF EVENING/OVERNIGHT TSTM DEVELOPMENT FROM
   THE ARKLATEX REGION TO IA.  ISOLATED HAIL/STRONG WIND GUSTS WILL BE
   POSSIBLE WITH THIS ACTIVITY.
   
   ...UPSTATE NY SWWD TO NWRN PA/NERN OH...
   WNWLY MID LEVEL WINDS ARE EXPECTED TO INCREASE ACROSS THIS REGION
   TODAY AS ONTARIO UPPER TROUGH MOVES EWD.  SURFACE DEWPOINTS IN THE
   LOWER 50S...CURRENTLY LOCATED ACROSS THE SRN GREAT LAKES REGION...
   ARE EXPECTED TO ADVECT NEWD AHEAD OF TRAILING COLD FRONT INTO THE
   LOWER GREAT LAKES /NERN OH TO WRN AND UPSTATE NY/.  ALTHOUGH MID
   LEVEL LAPSE RATES SHOULD BE WEAK...THIS LOW LEVEL MOISTURE AND
   SURFACE HEATING SUGGEST INSTABILITY SHOULD BE SUFFICIENT FOR A FEW
   STRONGER STORMS.  ISOLATED HAIL AND STRONG WIND GUSTS WILL BE THE
   PRIMARY THREATS.
   
   ..PETERS/JEWELL.. 04/23/2008
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z