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

   SPC AC 250601
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0101 AM CDT SAT APR 25 2009
   
   VALID 251200Z - 261200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS PORTIONS ERN PANHANDLE OF
   TX...WRN OK...SWRN KS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM NW TX TO CENTRAL
   KS THEN NEWD TO PORTIONS LOWER MI...
   
   ...SYNOPSIS...
   UPPER AIR PATTERN FCST TO FEATURE MEAN TROUGHING OVER WRN CONUS AND
   ERN RIDGING.  THIS PATTERN WILL SUPPORT CONTINUED LOW LEVEL MOISTURE
   ADVECTION/TRANSPORT ACROSS CENTRAL STATES...ALONG WITH PRESENCE OF
   WELL DEFINED FOCAL BOUNDARIES BENEATH AREAS OF FAVORABLE DEEP-LAYER
   WINDS.  AS SUCH...OVERALL SVR THREAT IS INCREASING COMPARED TO
   PREVIOUS DAYS.  MAIN FEATURE ALOFT FOR THIS FCST WILL BE MID-UPPER
   LEVEL LOW -- NOW ANALYZED OVER N-CENTRAL CA.  THIS FEATURE SHOULD
   PIVOT EWD FROM SWRN NV ACROSS AZ/UT BORDER AREA THROUGH 26/00Z. 
   MID-UPPER LOW THEN WILL DEAMPLIFY INTO OPEN-WAVE TROUGH AND LIFT
   NEWD OVER MUCH OF CO BY END OF PERIOD.  MEANWHILE...SECOND SHORTWAVE
   TROUGH -- INITIALLY EVIDENT IN MOISTURE CHANNEL IMAGERY OVER
   PORTIONS BC -- WILL DIG SEWD ACROSS NRN ROCKIES OF ID/MT.  WEAK/SRN
   STREAM PERTURBATION OVER AZ IS EXPECTED TO LIFT NEWD FROM NERN NM TO
   NWRN MO/SRN IA REGION DURING 25/12Z-26/00Z TIME FRAME. 
   MEANWHILE...UPPER TROUGH NOW OVER E TX IS FCST TO DRIFT EWD OVER
   SWRN AR AND LA.
   
   SFC COLD FRONT IS ANALYZED ATTM FROM LOWER MI SWWD ACROSS SRN
   WI...IA...EXTREME NWRN MO...AND PORTIONS N-CENTRAL/W-CENTRAL
   KS...THEN WWD INTO HYBRID LEE-SIDE/FRONTAL-WAVE CYCLONE NEAR LHX. 
   FRONT IS EXPECTED TO MOVE SEWD ACROSS LM/LH TO LOWER GREAT
   LAKES...WHILE DECELERATING ON ITS WRN END...RESULTING IN NET
   CLOCKWISE PIVOT OF ITS ORIENTATION.  BY 26/00Z...EXPECT COLD FRONT
   FROM SRN ONT AND SRN LOWER MI TO W-CENTRAL IL...BECOMING
   QUASISTATIONARY SWWD ACROSS PORTIONS ERN/SRN KS TO S-CENTRAL HIGH
   PLAINS.
   
   AS HAS BEEN TRUE FOR SEVERAL SERIES OF MODEL RUNS....CONSIDERABLE
   DIFFERENCES STILL EXIST WITH PROGGED MESOSCALE FRONTAL POSITIONS
   OVER S-CENTRAL HIGH PLAINS BETWEEN OPERATIONAL SPECTRAL AND
   NAM...LATTER BEING CLEARLY FARTHER S THAN SPECTRAL AS WELL AS 20 OF
   21 SREF MEMBERS...WHICH THEMSELVES VARY WIDELY.  GIVEN STRENGTH OF
   PRESSURE/HEIGHT FALLS EXPECTED ACROSS SRN ROCKIES REGION AHEAD OF
   MID-UPPER WAVE...AND RECENTLY OBSERVED VEERING OF 850 MB FLOW IN GLD
   VWP BEHIND SFC COLD FRONT...FCST WILL WEIGH STRONGLY TOWARD SREF
   CONSENSUS AND SOMEWHAT S OF SPECTRAL.  RESULTING ESTIMATE PLACES 00Z
   TRIPLE POINT INVOF NERN PANHANDLE OF TX...DRYLINE SWD ACROSS ERN
   PANHANDLE JUST W OF OK BORDER.  EWD DRYLINE BULGE MAY DEVELOP DURING
   AFTERNOON ACROSS ERN/NERN TX PANHANDLE...BEFORE SLGT NOCTURNAL
   RETREAT.  WRN SEGMENT OF FRONT SHOULD LIFT NWD OVER SWRN/CENTRAL KS
   AFTER DARK.
   
   ...CENTRAL/SRN PLAINS...
   SVR TSTMS...INCLUDING SUPERCELLS WITH POTENTIAL FOR VERY
   LARGE/DAMAGING HAIL AND A FEW TORNADOES...SHOULD DEVELOP LATE
   AFTERNOON INTO EARLY EVENING OVER ERN PANHANDLES AND WRN OK
   REGION....MOVING NEWD AND INCREASING IN COVERAGE AFTER DARK.
   WITHIN THIS REGION...SMALL AREA OF IDEALLY JUXTAPOSED FOCI AND
   PARAMETERS FOR TORNADIC SUPERCELLS MAY TAKE SHAPE AROUND 00Z AND
   INTO EVENING...NEAR TRIPLE POINT AND SOMEWHAT SWD ALONG/AHEAD OF
   DRYLINE.  THREAT FOR SVR...ALONG WITH LIKELY CONVECTIVE
   COVERAGE...BECOMES MORE CONDITIONAL WITH SWD EXTENT INVOF DRYLINE
   INTO NW TX BECAUSE OF CAP STRENGTH AT BASE OF ELEVATED MIXED LAYER
   AIR MASS.  HIGH CLOUDS MAY RESTRICT SFC HEATING SOMEWHAT FOR MUCH OF
   DAY...ESPECIALLY AHEAD OF EJECTING SRN STREAM THROUGH...WITH WEAK
   SUBSIDENCE ALOFT IN WAKE OF THAT PERTURBATION THROUGH MID-AFTERNOON.
    DURING 21-00Z TIME FRAME...LOW-MID 60S SFC DEW POINTS MAY BECOME
   AVAILABLE TO CONVECTION FROM TRIPLE POINT REGION SWD...COMBINING
   WITH STEEP MIDLEVEL LAPSE RATES TO CONTRIBUTE TO MLCAPE IN 1500-2500
   J/KG RANGE.  EFFECTIVE SHEAR 40-45 KT SHOULD SUPPORT SUPERCELL
   STRUCTURES ALONG WITH 0-1 KM SRH 150-250 J/KG BEFORE 00Z.
   
   CONDITIONAL POTENTIAL EXISTS FOR STG TORNADOES...ESPECIALLY JUST
   AFTER DARK WHEN LLJ STRENGTHENS APPRECIABLY...YET SUFFICIENTLY RICH
   THETAE REMAINS TO KEEP EFFECTIVE INFLOW PARCELS ROOTED AT SFC. 
   PATTERN RESEMBLES THAT WHICH HAS YIELDED REGIME OF ONE OR TWO
   SIGNIFICANT/NOCTURNAL TORNADIC SUPERCELLS HISTORICALLY.  LLJ-RELATED
   BOOST IN HODOGRAPH SIZE MAY LEAD TO 300-500 J/KG OF 0-1 KM SRH BY
   ABOUT 26/03Z.  MAIN UNCERTAINTY ATTM IS IN COVERAGE/NUMBER OF STORMS
   AND RESULTING INFLUENCE ON STRUCTURE OF SUPERCELLS...WHICH MAY TEND
   TOWARD HEAVY-PRECIP CHARACTER AFTER DARK.  THEREFORE WILL WAIT FOR
   ADDITIONAL INDICATIONS TO INTRODUCE AOA 10-PERCENT
   SIGNIFICANT-TORNADO PROBABILITIES.
   
   NOCTURNAL/NWD SPREAD OF FAVORABLE WARM SECTOR AIR MASS ACROSS KS MAY
   BE AFFECTED ON MESOSCALE BY CONVECTION OVER WRN/NWRN OK AND KS
   BORDER REGION...LENDING SOME UNCERTAINTY TO SVR POTENTIAL.  WHILE
   SIGNIFICANT NOCTURNAL SUPERCELL EVENT CANNOT BE RULED OUT OVER
   W-CENTRAL KS...THESE UNCERTAINTIES WILL KEEP GREATEST PROBABILITIES
   SHUNTED FARTHER S ATTM.
   
   SEPARATE AREA OF STG-SVR CONVECTION MAY DEVELOP OVER CENTRAL HIGH
   PLAINS AND MOVE NEWD OVER NEB OVERNIGHT...SUPPORTED BY ELEVATED LOW
   LEVEL WAA AND FAVORABLE EFFECTIVE SHEAR.  ATTM HAIL APPEARS TO BE
   MAIN CONCERN...AND AT LEAST MRGL SVR PROBABILITIES ARE WARRANTED.
   
   ...FRONTAL ZONE -- SRN/CENTRAL KS TO GREAT LAKES...
   SCATTERED TSTMS SHOULD DEVELOP DURING AFTERNOON/EARLY EVENING
   DIURNALLY JUST ABOUT ANYWHERE WITHIN FRONTAL ZONE...AMIDST STG SFC
   HEATING AND FAVORABLE MOISTURE WARM SIDE...AND FAVORABLE DEEP-LAYER
   SHEAR.  ADDITIONAL SUPPORT ALOFT MAY BE PROVIDED IN FORM OF ENHANCED
   LARGE SCALE ASCENT AHEAD OF EJECTING MINOR SHORTWAVE.  INITIAL
   SUPERCELL STRUCTURES ARE POSSIBLE...WITH MORE LINEAR/BANDED
   EVOLUTION EXPECTED TO DEVELOP.  DAMAGING GUSTS AND LARGE HAIL ARE
   MAIN THREATS...WITH VERY CONDITIONAL/MRGL TORNADO POTENTIAL TIED TO
   LOCALIZED STORM SCALE EFFECTS.  THREAT SHOULD DIMINISH AFTER DARK --
   EXCEPT OVER KS WHERE MOIST/60 KT LLJ SHOULD SUPPORT SVR MCS
   EVOLUTION FROM DIURNAL ACTIVITY DESCRIBED ABOVE.
   
   ...ERN OK/ARKLATEX REGION TO UPPER TX COASTAL PLAIN...
   WEAK SBCINH IS EXPECTED OVER THIS REGION...WHICH WILL BE LOCATED OFF
   ERN EDGE OF ELEVATED MIXED LAYER AIR MASS.  STG HEATING
   BENEATH...AND PERHAPS JUST W OF...MID-UPPER TROUGH WILL CONTRIBUTE
   TO DEVELOPMENT OF DIURNAL CONVECTION OVER THIS REGION...ALONG WITH
   SUBTLE SFC BOUNDARIES LEFT OVER FROM PRIOR ACTIVITY.  FCST WIND
   PROFILES ARE CHARACTERIZED BY STG LOW LEVEL SHEAR BUT PRONOUNCED
   KINEMATIC WEAKNESSES ALOFT.  EXPECT ISOLATED HAIL/GUSTS NEAR SVR
   LEVELS...AND VERY LOW/CONDITIONAL TORNADO THREAT.
   
   ...ERN GREAT BASIN TO WRN CO...
   BAND OF TSTMS MAY DEVELOP JUST AHEAD OF UPPER LOW/TROUGH DURING
   EARLY-MID-AFTERNOON...MOVING RAPIDLY ENEWD WITH POTENTIAL FOR
   STG-SVR GUSTS.  STG LARGE SCALE ASCENT...RELATED STEEPENING OF LAPSE
   RATES...AND MRGL LOW LEVEL MOISTURE SHOULD CONTRIBUTE TO MLCAPE
   100-500 J/KG IN SUPPORT OF CONVECTION ACROSS THIS REGION. POTENTIAL
   SHOULD DIMINISH RAPIDLY BY AROUND 00Z AS SFC COOLING TAKES PLACE
   OVER HIGH TERRAIN OF WRN CO...IN PATH OF THIS ACTIVITY.
   
   ...CENTRAL/SRN APPALACHIANS...
   ISOLATED TO WIDELY SCATTERED TSTMS SHOULD DEVELOP DIURNALLY...AMIDST
   AT LEAST MRGLLY FAVORABLE LOW LEVEL MOISTURE AND STG SFC HEATING OF
   ELEVATED TERRAIN.  GIVEN PROXIMITY TO UPPER RIDGE...FCST SOUNDINGS
   REASONABLY SUGGEST WEAK DEEP-LAYER WINDS...SUPPORTING
   PULSE/MULTICELL ORGANIZATION AND OUTFLOW DOMINANCE.  DOWNBURSTS AND
   ISOLATED HAIL ARE POSSIBLE.
   
   ...WRN/CENTRAL/NRN NY...PORTIONS WRN NEW ENGLAND...
   WEAKENING SBCINH THROUGHOUT DAYLIGHT HOURS...ALONG WITH LOW LEVEL
   MOIST ADVECTION...MAY LEAD TO WIDELY SCATTERED TSTMS OVER THIS
   REGION.  ALTHOUGH MRGL BOUNDARY LAYER MOISTURE SHOULD KEEP MLCAPE TO
   BELOW 1000 J/KG...WELL-MIXED SUBCLOUD LAYERS AND RELATED
   EVAPORATIONAL COOLING MAY ENHANCE DOWNDRAFTS ENOUGH FOR MRGL SVR
   WIND CONCERN.  NEARLY UNIDIRECTIONAL DEEP-LAYER WINDS FAVOR
   EWD-MOVING CELLS AND SHORT LINE SEGMENTS.
   
   ..EDWARDS/GARNER.. 04/25/2009
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z