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

   SPC AC 251257
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0757 AM CDT SAT APR 25 2009
   
   VALID 251300Z - 261200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF WRN OK...SRN
   KS...AND THE OK/TS PANHANDLES...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA
   FROM NW TX NE INTO LWR MI...
   
   ...SYNOPSIS...
   SW MID/UPR LVL FLOW WILL CONTINUE OVER THE CNTRL STATES...
   DOWNSTREAM FROM FAIRLY STRONG UPR LOW NOW IN NV.  THE LOW SHOULD
   EVOLVE INTO AN OPEN WAVE LATER TODAY...AND ACCELERATE ENE TO THE
   CNTRL HI PLNS BY 12Z SUN.  FARTHER S...WEAK SRN STREAM VORT SHOULD
   FURTHER WEAKEN AS IT CONTINUES SLOWLY E FROM E TX TO THE LWR MS VLY.
   
   
   AT THE SFC...COLD FRONT NOW EXTENDING FROM THE UPR GRT LKS TO THE
   NRN TX PANHANDLE SHOULD BE THE MAIN FOCUS FOR SVR TSTMS THIS PERIOD.
    THE FRONT SHOULD MOVE STEADILY SE ACROSS WI/MI TO LWR GRT LKS
   THROUGH EARLY SUN.  THE WRN PART OF THE BOUNDARY...MEANWHILE
   ...SHOULD DECELERATE LATER TODAY AND RETURN N ACROSS THE CNTRL PLNS
   TONIGHT/EARLY SUN AS UPR TROUGH APPROACHES FROM THE GRT BASIN.
   
   ...CNTRL/SRN PLNS...
   SVR TSTMS...INCLUDING SUPERCELLS WITH POTENTIAL FOR VERY
   LARGE/DAMAGING HAIL AND A FEW TORNADOES...SHOULD DEVELOP LATE THIS
   AFTN THROUGH EARLY TONIGHT OVER THE ERN TX/OK PANHANDLES AND WRN OK.
    THE STORMS SHOULD MOVE NE AND INCREASE IN COVERAGE AFTER DARK.  IN
   THE MDT RISK AREA...POTENTIAL WILL EXIST FOR TORNADIC SUPERCELLS
   NEAR INTERSECTION OF STALLING SFC FRONT AND LEE TROUGH/DRY LINE.  AN
   INCREASINGLY CONDITIONAL THREAT /DUE TO EML CAP/ WILL EXTEND SWD
   ALONG DRY LINE TOWARD NW TX.
   
   SATELLITE SUGGESTS THAT HIGH CLOUDS WITH WEAK LEAD IMPULSE AHEAD OF
   MAIN NV UPR VORT SHOULD EXIT THE TX/OK PANHANDLE REGION BY LATE THIS
   MORNING...ALLOWING FOR CONSIDERABLE SFC HEATING LATER TODAY. 
   LOW-MID 60S SFC DEW POINTS HAVE BECOME WELL ESTABLISHED ACROSS NW TX
   AND MUCH OF OK...AND WILL CONTINUE TO SPREAD NW TOWARD APPROACHING
   COLD FRONT THROUGH THE DAY.  COMBINED WITH STEEP MID LVL LAPSE
   RATES...SETUP SHOULD YIELD AFTN SBCAPE AOA 2000 J/KG.  AT THE SAME
   TIME...40-50 KT WSWLY MID LVL FLOW WILL CONTRIBUTE TO SUBSTANTIAL
   DEEP WLY SHEAR...WITH 0-1 KM SRH OF 150-250 M2/S2 LIKELY BEFORE 00Z.
   
   
   A CONDITIONAL POTENTIAL WILL EXIST FOR STG TORNADOES...ESPECIALLY
   JUST AFTER DARK WHEN SSWLY LLJ APPRECIABLY STRENGTHENS... SEASONABLY
   RICH MOISTURE INFLOW CONTINUES /KEEPING STORMS SFC-BASED/...AND
   LARGE SCALE ASCENT INCREASE WITH CONTINUED ENE MOVEMENT OF GRT BASIN
   UPR TROUGH.  THE PATTERN RESEMBLES PAST EPISODES THAT HAVE PRODUCED
   ONE OR TWO STRONG NOCTURNAL TORNADOES IN THE REGION.  LLJ-RELATED
   BOOST IN HODOGRAPH SIZE MAY YIELD 300-500 M2/S2 0-1 KM SRH BY MID
   EVE.
   
   NOCTURNAL/NWD SPREAD OF FAVORABLE WARM SECTOR AIR MASS NWD ACROSS KS
   MAY BE AFFECTED ON THE MESOSCALE BY STORMS OVER WRN/NW OK AND SRN
   KS...LENDING TO SOME UNCERTAINTY REGARDING DEGREE OF OVERNIGHT SVR
   IN CNTRL/ERN KS.  NEVERTHELESS...STRENGTHENING WIND FIELD AND ASCENT
   WITH APPROACHING UPR TROUGH...AND CONTINUED RICH MOISTURE
   INFLOW...SUGGEST A BETTER THAN EVEN RISK FOR A CONTINUING SVR THREAT
   /HAIL...WIND..AND ISOLD TORNADOES/ INTO EARLY SUN IN KS.
   
   FARTHER N...A SEPARATE AREA OF STG-SVR CONVECTION MAY DEVELOP OVER
   CENTRAL HI PLNS AND MOVE NE OVER NEB OVERNIGHT...SUPPORTED BY
   ELEVATED LOW LVL WAA AND FAVORABLE SHEAR.  ATTM HAIL APPEARS TO BE
   MAIN CONCERN.
   
   ...SRN/CNTRL KS NE TO LWR MI...
   SCTD SFC-BASED TSTMS SHOULD FORM THIS AFTN THROUGH EARLY TONIGHT
   ALONG AFOREMENTIONED FRONTAL ZONE FROM NE KS TO LWR MI.  ENVIRONMENT
   WILL BE CHARACTERIZED BY 30-40 KT DEEP WSWLY SHEAR ON SRN FRINGE OF
   NRN STREAM JET...AND 1500-2000 J/KG SBCAPE. DEVELOPMENT MAY BE
   ASSISTED BY ASCENT IN RIGHT ENTRANCE REGION OF SPEED MAX CROSSING
   THE UPR GRT LKS.
   
   A FEW SUPERCELLS WILL BE POSSIBLE INITIALLY...BUT DOMINANT EVOLUTION
   SHOULD BE TOWARD BROKEN LINEAR/BANDED STRUCTURES WITH EMBEDDED
   BOWING SEGMENTS YIELDING SVR WIND/HAIL...ESPECIALLY IN LWR MI. 
   ISOLD TORNADOES WILL BE POSSIBLE...BUT LIKELY TIED TO LOCALIZED
   STORM SCALE EFFECTS.  THE SVR THREAT SHOULD DIMINISH AFTER
   DARK...EXCEPT OVER CNTRL/ERN KS WHERE MOIST/60 KT LLJ LIKELY WILL
   SUPPORT AN OVERNIGHT SVR MCS EVOLUTION FROM THE SRN PLNS STORMS
   DESCRIBED ABOVE.
   
   ...SE TX INTO ARKLATEX/ERN OK...
   WEAK CIN IS EXPECTED OVER THIS REGION...WHICH WILL BE LOCATED ON ERN
   FRINGE OF ELEVATED MIXED LAYER.  STG HEATING INVOF SRN STREAM UPR
   TROUGH AND/OR ALONG SUBTLE BOUNDARIES LEFT FROM PRIOR CONVECTION
   WILL LEAD TO SCTD CLUSTERS OF DIURNAL STORMS.  WIND PROFILES SHOULD
   EXHIBIT CONSIDERABLE LOW LVL SHEAR...BUT WEAKER FLOW ALOFT.  COUPLED
   WITH RICH LOW LVL MOISTURE /AVERAGE PW OVER REGION NOW AOA 1.25
   INCHES/...SETUP COULD YIELD A FEW SPOTS OF SVR HAIL/WIND...IN
   ADDITION TO A LOW/CONDITIONAL TORNADO THREAT.
   
   ...CNTRL/ERN UT INTO WRN CO...
   A BAND OF TSTMS SHOULD FORM OVER CNTRL/ERN UT THIS AFTN...JUST AHEAD
   OF NV UPR VORT/TROUGH.  THE LINE SHOULD MOVE RAPIDLY ENE...WITH
   MODERATE UNIDIRECTIONAL SSW FLOW AND SIZABLE TEMPERATURE-DEWPOINT
   SPREADS POSSIBLY PRODUCING A FEW STG/SVR GUSTS.  SUSTAINED MESOSCALE
   ASCENT AND ASSOCIATED STEEPENING OF MID LVL LAPSE RATES SHOULD YIELD
   100-500 J/KG MLCAPE DESPITE LIMITED MOISTURE.  THE LINE SHOULD
   WEAKEN AFTER 00Z AS IT MOVES TOWARD CNTRL CO.
   
   ...CNTRL/SRN APPALACHIANS...
   ISOLD TO WDLY SCTD DIURNAL STORMS SHOULD FORM IN ENVIRONMENT OF
   MODEST LOW LVL MOISTURE AND STG SFC HEATING/STEEP LOW LVL LAPSE
   RATES OVER ELEVATED TERRAIN.  PROXIMITY OF UPR RIDGE WILL KEEP DEEP
   WIND FIELD WEAK.  BUT PULSE/MULTICELL STORMS COULD YIELD A FEW LOCAL
   DOWNBURSTS/SVR HAIL EVENTS.
   
   ...WRN/CNTRL/NRN NY AND NW WRN NEW ENGLAND...
   WEAKENING CIN THROUGH THE DAY...ALONG WITH LOW LVL MOIST INFLOW FROM
   THE WSW...MAY LEAD TO WDLY SCTD DIURNAL STORMS OVER THE
   REGION.  LIMITED BOUNDARY LAYER MOISTURE WILL KEEP MLCAPE TO
   BELOW 1000 J/KG DESPITE RELATIVELY STEEP MID LVL LAPSE RATES.  BUT
   WELL-MIXED SUB CLOUD LAYER AND RELATED EVAPORATIONAL COOLING MAY
   ENHANCE DOWNDRAFTS ENOUGH FOR A MRGL SVR WIND CONCERN.  NEARLY
   UNIDIRECTIONAL DEEP WIND FIELD WILL FAVOR EWD-MOVING CELLS AND SHORT
   LINE SEGMENTS.
   
   ..CORFIDI/SMITH.. 04/25/2009
   
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