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

   SPC AC 261337
   
   DAY 1 CONVECTIVE OUTLOOK CORR 1
   NWS STORM PREDICTION CENTER NORMAN OK
   0837 AM CDT SUN APR 26 2009
   
   VALID 261300Z - 271200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF TX...OK...AND
   KS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA
   FROM S CNTRL TX INTO THE LWR MO/MID MS VLYS...
   
   CORRECTED DEWPOINTS IN NY/PA/MA/CT
   
   ...SYNOPSIS...
   A SERIES OF SPEED MAXIMA EJECTING NEWD ON ERN SIDE OF SLOWLY-
   PROGRESSIVE WRN U.S. TROUGH WILL PRODUCE MULTIPLE EPISODES OF SVR
   TSTMS OVER A FAIRLY BROAD SWATH OF THE CNTRL AND S CNTRL U.S.
   THROUGH EARLY MON.
   
   MAIN UPR VORT NOW OVER WY/CO SHOULD CONTINUE NE INTO THE DAKOTAS/NEB
   LATER TODAY AS TRAILING/LOOSELY-ASSOCIATED SRN IMPULSE NOW IN NM
   REACHES W TX.  THE LATTER FEATURE SHOULD CONTINUE NE INTO THE LWR MO
   VLY/WRN OZARKS BY 12Z MON...WHILE ADDITIONAL IMPULSES OF MORE SRN
   ORIGIN MOVE ENE ACROSS WRN/CNTRL TX.
   
   AT LWR LVLS...ERN PART OF MAIN SYNOPTIC SCALE FRONT NOW EXTENDING
   FROM SW KS TO THE MID MS VLY SHOULD SURGE NE INTO WI AND THE UPR GRT
   LKS BY EARLY MON AS A SFC WAVE DEVELOPS OVER SE NEB AND MOVES NE IN
   ASSOCIATION WITH LEAD UPR IMPULSE.  IN THE WAKE OF THE WAVE...
   EXPECT TRAILING WRN PART OF THE FRONT WILL ACCELERATE SE ACROSS
   WRN/NRN KS AND THE OK/NRN TX PANHANDLE REGION EARLY MON.  FARTHER
   S...STRONG/PERSISTENT SW FLOW ALOFT WILL MAINTAIN LEE LOW AND
   TROUGH/DRY LINE OVER THE SRN HI PLNS.
   
   ...SRN PLNS INTO CNTRL KS...
   SLOW EWD PROGRESSION OF WRN STATES TROUGH...AND ASSOCIATED ARRAY OF
   SPEED MAXIMA...WILL MAINTAIN A BROAD CURRENT OF 55-65 KT MID LVL
   SSWLY FLOW OVER MOST THE SRN AND CNTRL PLNS THROUGH THE PERIOD. 
   THUS...DEEP SHEAR WILL BE FAVORABLE FOR SUSTAINED STORMS/ SUPERCELLS
   OVER A WIDE REGION.  BUT SATELLITE LOOPS SUGGEST THE PRESENCE OF
   NUMEROUS WEAK SHORT WAVE DISTURBANCES WITHIN THIS FLOW...IN ADDITION
   TO THE MORE OBVIOUS ONES MENTIONED IN THE SYNOPSIS.  THESE LIKELY
   WILL MODULATE STORM DEVELOPMENT AND EVOLUTION ON THE MESOSCALE...AND
   WILL ADD CONSIDERABLE COMPLEXITY TO THE GENERAL SCENARIO OUTLINED
   BELOW.
   
   ONE APPARENT IMPULSE...NOW IN CNTRL OK...APPEARS RESPONSIBLE IN PART
   FOR RECENT INCREASE IN STORMS ALONG ADVANCING WARM FRONT IN CNTRL
   KS.  EXPECTED THIS ACTIVITY TO INCREASE BOTH NEWD AND SWWD ALONG
   FRONT THROUGH THE MORNING AS STRONG/MOIST SLY LLJ CONTINUES TO
   IMPINGE ON BOUNDARY.
   
   A BIT LATER THIS MORNING THROUGH EARLY THIS AFTN...EXPECT THAT
   ASCENT WITH STRONGER NM IMPULSE WILL HELP INITIATE STORMS ALONG LEE
   TROUGH/DRY LINE FROM THE ERN TX PANHANDLE/NW OK SSW TO THE PERMIAN
   BASIN.  SFC HEATING ON WRN EDGE OF EXTENSIVE LOW CLOUD FIELD...AND
   WEAK HEIGHT FALLS/MID LVL COOLING...SHOULD ALLOW THIS ACTIVITY TO
   INCREASE IN COVERAGE/STRENGTH THROUGH LATE THIS AFTN/EVE.
   
   COMBINATION OF STRONG INSTABILITY /SBCAPE TO 2000 J PER KG/ AND RICH
   MOISTURE /PW 1.00-1.25 INCHES/ WITH 40-50 KT DEEP SWLY SHEAR SHOULD
   SUPPORT SCTD SUSTAINED SUPERCELLS WITH SVR HAIL AND WIND.
   INITIALLY...BACK-VEER PATTERN TO WIND PROFILES ACROSS THE SRN HI
   PLNS /E.G AS IN 12Z MAF RAOB/ WILL COMPLICATE STORM STRUCTURE/ FAVOR
   LINE SEGMENTS.  ALTHOUGH THIS MAY LIMIT POTENTIAL FOR
   TORNADOES...GIVEN STRENGTH OF SHEAR AND QUALITY OF MOIST INFLOW...AT
   LEAST A CONDITIONAL TORNADO THREAT WILL EXIST.
   
   BY LATE AFTN OR EARLY EVE...EXPECT THAT THE STORMS WILL HAVE EVOLVED
   INTO SEVERAL LOOSELY-ORGANIZED CLUSTERS EXTENDING FROM CNTRL/SRN KS
   THROUGH WRN/CNTRL OK INTO NRN/W CNTRL AND SW TX.  EMBEDDED
   SUPERCELLS WITHIN THESE CLUSTERS WILL CONTINUE TO POSE A THREAT FOR
   SVR HAIL/WIND AND TORNADOES.  THE TORNADO THREAT MAY ONCE AGAIN
   INCREASE TOWARD SUNSET AND LATER AS SLY LLJ STRENGTHENS TO AOA 50
   KTS.
   
   GIVEN THE MAGNITUDE OF THE SHEAR AND THE BREADTH/QUALITY/STRENGTH OF
   THE MOIST INFLOW...THE SVR THREAT MAY CONTINUE THROUGH LATE
   TONIGHT/EARLY MON NEWD ACROSS ERN OK AND ERN KS.  FARTHER S...OTHER
   SVR STORMS/STORM CLUSTERS MAY CONTINUE TO EVOLVE OVER N
   CNTRL...CNTRL...AND S CNTRL TX AS AFOREMENTIONED SRN STREAM
   DISTURBANCES INTERACT WITH STRONG/MOISTURE RICH SLY FLOW.
   
   ...ERN KS TO UPR MS VLY/GRT LKS...
   STORMS NOW FORMING N OF WARM FRONT WILL CONTINUE TO POSE A THREAT
   FOR SVR HAIL.  50-60 KT SSWLY LLJ WILL BE MAINTAINED AND SHIFT NNE 
   TO THE UPR MS VLY AS LEAD SHORT WAVE IMPULSE EJECTS NEWD. GIVEN
   STRENGTH OF THE LLJ...A RELATIVELY NARROW CORRIDOR OF RICH
   MOISTURE SHOULD MOVE RAPIDLY NNE...WITH SFC DEWPOINTS IN THE LOWER
   60S REACHING SERN MN/CNTRL WI BY MID-LATE AFTN.  EXTENT OF
   DESTABILIZATION ALONG THIS AXIS REMAINS UNCERTAIN DUE TO CLOUDS AND
   LIKELIHOOD FOR ADDITIONAL ELEVATED CONVECTION.  NEVERTHELESS...SOME
   BOUNDARY LAYER WARMING WILL OCCUR IN WAKE OF MORNING RAIN...WITH
   MLCAPE OF 500-1000 J/KG POSSIBLE.  STORMS SHOULD INTENSIFY ALONG AND
   POSSIBLY AHEAD OF FRONT FROM KS NEWD THROUGH IA AS BOUNDARY RETURNS
   SEWD IN WAKE OF SFC WAVE.
   
   STRONG WIND PROFILES WITH EJECTING IMPULSE AND ATTENDANT LLJ WILL
   RESULT IN LARGE HODOGRAPHS /0-1 KM SRH 200-300 M2 PER S2/...WITH 
   SUFFICIENT DEEP SHEAR FOR ORGANIZED STORMS...LIKELY BROKEN LINES
   WITH EMBEDDED BOWING SEGMENTS AND SUPERCELLS.  THESE WILL POSE A
   THREAT FOR DMGG WIND AND ISOLD TORNADOES/HAIL.  THIS ACTIVITY MAY
   MERGE WITH OTHER CLUSTERS MOVING/DEVELOPING NEWD ACROSS ERN KS AND
   NW MO EARLY MON.
   
   INSTABILITY WILL DECREASE GRADUALLY WITH NEWD EXTENT INTO NRN WI/UPR
   MI...ISOLD SVR WIND GUSTS MAY OCCUR CLOSE TO STRONG LLJ  EARLY MON.
   
   ...PARTS OF UPSTATE NY/NE PA/WRN MA AND CT...
   SFC DEWPOINTS IN THE MID 50S WILL SPREAD E ACROSS THE PRE-FRONTAL
   WARM SECTOR OVER SRN NY INTO SRN NEW ENGLAND.  MODEST MID LVL LAPSE
   RATES AROUND 6.5 C/KM ARE EXPECTED TO LIMIT DEGREE OF
   DESTABILIZATION.  HOWEVER...POTENTIAL WILL EXIST FOR A FEW
   HIGH-BASED TSTMS THIS AFTN/EARLY EVE...WITH ACTIVITY SPREADING E
   GIVEN 30-40 WLY MID LVL FLOW.  STEEP LOW LEVEL LAPSE RATES/WELL
   MIXED BOUNDARY LAYER SUGGESTS POSSIBILITY FOR A FEW STRONGER WIND
   GUSTS.
   
   ..CORFIDI/HART/SMITH/MEAD.. 04/26/2009
   
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