May 18, 2011 2000 UTC Day 1 Convective Outlook
Updated: Wed May 18 20:01:06 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20110518 2000 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110518 2000 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Probabilistic Damaging Wind Graphic
20110518 2000 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Probabilistic Large Hail Graphic
20110518 2000 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
   SPC AC 181956
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0256 PM CDT WED MAY 18 2011
   
   VALID 182000Z - 191200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE CENTRAL
   AND SOUTHERN PLAINS...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER OH VALLEY EWD
   INTO THE MID ATLANTIC STATES...
   
   ...CENTRAL/SRN PLAINS...
   AT 19Z..SURFACE LOW APPEARS TO BE LOCATED IN THE FAR ERN TX
   PANHANDLE...WITH WARM FRONT EXTENDING EWD INTO N CENTRAL OK AND THEN
   SEWD INTO THE ARKLATEX REGION. AT THE SAME TIME...SUNNY SKIES AND
   CONSEQUENT STRONGLY WARMING TEMPERATURES AND MIXING HAD RESULTED IN
   THE DRYLINE TO PROGRESS EWD FROM NEAR CUSTER CO...OK SWD TO NEAR
   ABI. THE WELL MIXED AIR MASS HAD RESULTED IN CU TO DEVELOP NEAR THIS
   BOUNDARY AND GIVEN THE MOIST UNSTABLE AIR MASS SITUATED JUST EAST OF
   THE BOUNDARY...ISOLATED STORMS MAY DEVELOP SOON. HOWEVER...PROFILERS
   IN THE AREA SHOW WINDS ARE BACKING AND SIGNIFIES THAT THE DRYLINE
   MAY NOT MOVE FURTHER EWD. ALSO ANY STORMS THAT DEVELOP WILL QUICKLY
   ENCOUNTER A MORE CLOUDY AND LIKELY MORE CAPPED ENVIRONMENT ALONG AND
   EAST OF I-35. HOWEVER...STORMS THAT DO DEVELOP SHOULD EVOLVE INTO
   SUPERCELLS WITH A THREAT FOR VERY LARGE HAIL...WIND DAMAGE AND EVEN
   A FEW TORNADOES.
   
   WV/IR IMAGERY SHOWS CIRRUS CLOUDS SPREADING RAPIDLY NEWD FROM ERN NM
   INTO THE TX PANHANDLE. THIS MAY BE INDICATIVE OF A HIGH LEVEL SPEED
   MAX AND MAY AID IN CONVECTIVE INITIATION FROM FAR SERN CO SEWD INTO
   NWRN OK. THIS STRONGER DYNAMICAL FORCING WILL OVERSPREAD KS TONIGHT
   AND RESULT IN STRENGTHENING LOW LEVEL JET/WARM ADVECTION. ELEVATED
   STORMS ARE EXPECTED IN THIS REGION AND THE SHEAR/INSTABILITY
   COMBINATION MAY BE SUFFICIENT FOR STORMS WITH SEVERE HAIL...SO THE
   SLIGHT RISK HAS BEEN EXPANDED NEWD ACROSS MUCH OF KS FOR THE
   OVERNIGHT PERIOD.
   
   ...UPPER OH VALLEY EWD TO THE MID ATLANTIC STATES...
   THE COMBINATION OF AFTERNOON HEATING AND FORCING ASSOCIATED WITH
   SHORTWAVE TROUGH ROTATING NNWWD ACROSS NRN WV HAD AIDED IN STRONGER
   STORM DEVELOPMENT OVER THE REGION...REFERENCE MCD 0803.  THE SLIGHT
   RISK HAS BEEN EXTENDED WWD INTO NRN OH WHERE EARLIER PARTLY CLOUDY
   SKIES AID IN WARMING TEMPERATURES WELL INTO THE 60S. THE SLIGHT RISK
   WAS ALSO EXTENDED INTO MORE OF PA AND NJ WHERE BAND OF CONVECTION
   WAS MOVING ONSHORE IN FAVORABLE SHEAR FOR SOME MID LEVEL ROTATION
   AND A BRIEF TORNADO OR TWO.
   
   ...NERN CO...
   AN ISOLATED SEVERE STORM HAS RECENTLY DEVELOPED IN NERN CO NEAR DEN.
   DESPITE COOL AIR MASS...MUCAPES NEAR 500 J/KG AND STRONGLY VEERING
   WIND PROFILES ARE FAVORABLE FOR SUPERCELL STRUCTURES. THE PRIMARY
   SEVERE THREAT SHOULD BE HAIL. THE INSTABILITY DROPS OFF RAPIDLY EAST
   OF THE DEN-FCL CORRIDOR...SO THE SEVERE THREAT SHOULD MAINLY BE NEAR
   THE FOOTHILLS THE NEXT COUPLE OF HOURS.
   
   ..IMY.. 05/18/2011
   
   .PREV DISCUSSION... /ISSUED 1131 AM CDT WED MAY 18 2011/
   
   ...CNTRL/SRN PLAINS...
   
   POTENT VORTICITY MAXIMUM AND ASSOCIATED MID AND HIGH-LEVEL JET
   STREAKS DIGGING SEWD INTO THE LOWER CO VALLEY WILL ROUND LARGE-SCALE
   TROUGH BASE TODAY...REACHING THE CNTRL/SRN HIGH PLAINS BY 19/12Z. 
   THERE IS SOME INDICATION THAT A WEAKER LEAD IMPULSE MAY BE LOCATED
   NEAR THE FOUR CORNERS REGION WHICH WOULD TRANSLATE NEWD INTO THE
   CNTRL HIGH PLAINS THIS EVENING.  IN THE LOW LEVELS...SURFACE CYCLONE
   OVER W-CNTRL OK AS OF MID MORNING WILL BECOME MORE ELONGATED WITH
   TIME AS PRESSURE CONTINUES TO FALL OVER THE SRN HIGH PLAINS. 
   DRYLINE WILL MIX EWD AND WILL LIKELY EXTEND FROM INTERSECTION WITH
   WARM FRONT OVER NWRN OK SEWD TO JUST W OF THE OKC AREA AND THEN SWWD
   INTO W-CNTRL TX BY LATE AFTERNOON.
   
   SLY LOW-LEVEL FLOW E OF DRYLINE WILL SUPPORT THE NWD FLUX OF AN
   INCREASINGLY MOIST BOUNDARY LAYER TODAY WITH DEWPOINTS RISING INTO
   THE LOWER/MID 60S.  THIS MOISTURE COUPLED WITH DAYTIME HEATING AND
   MODESTLY STEEP MIDLEVEL LAPSE RATES WILL YIELD A MODERATELY UNSTABLE
   AIR MASS BY AFTERNOON WITH MLCAPE VALUES APPROACHING 2000-2500 J/KG.
    LATEST MESOSCALE AND CONVECTION-ALLOWING MODEL GUIDANCE REMAIN
   CONSISTENT IN SUGGESTING THAT THE COMBINATION OF STRONG DIABATIC
   HEATING W OF DRYLINE AND POTENTIAL INFLUENCE OF ABOVE-MENTIONED LEAD
   IMPULSE WILL CONTRIBUTE TO ISOLATED STORM DEVELOPMENT LATER TODAY. 
   GIVEN FORECAST VERTICALLY VEERING WIND PROFILES WITH 40-50 KT OF
   DEEP WLY SHEAR AND 0-1 KM SRH OF 100-200 M2/S2...SETUP WILL FAVOR
   SUPERCELL DEVELOPMENT WITH ATTENDANT RISKS FOR VERY LARGE HAIL...A
   COUPLE TORNADOES AND LOCALLY DAMAGING WINDS.
   
   ELSEWHERE...A CONDITIONAL THREAT FOR ISOLATED SEVERE STORMS WILL
   EXIST ALONG BENT-BACK SEGMENT OF WARM FRONT EXTENDING FROM NWRN OK
   INTO ERN CO THIS AFTERNOON INTO TONIGHT.  HERE TOO...KINEMATIC
   ENVIRONMENT WILL BE SUPPORTIVE OF SUPERCELLS CAPABLE OF LARGE HAIL
   AND PERHAPS A TORNADO.  
   
   ...UPPER OH VALLEY INTO MID ATLANTIC STATES...
   
   MORNING WATER VAPOR IMAGERY SHOWS THE NEXT VORTICITY MAXIMUM
   PIVOTING AROUND UPPER LOW WITH THIS FEATURE LIKELY PROGRESSING NWWD
   FROM VA/WV INTO THE UPPER OH VALLEY.  SUPPLEMENTAL 14Z IAD SOUNDING
   INDICATES THAT THE AIR MASS IS ALREADY MODERATELY UNSTABLE FOR A
   SURFACE-BASED PARCEL /I.E. SBCAPE OF 1000-1500 J PER KG/.  SIMILAR
   TO TUESDAY...DEEPER PBL MIXING WILL LIKELY RESULT IN DEWPOINTS
   DECREASING THROUGH THE AFTERNOON.  HOWEVER...CONTINUED DAYTIME
   HEATING SHOULD OFFSET THIS TO SOME DEGREE...MAINTAINING SIMILAR
   SBCAPE VALUES ACROSS SLIGHT RISK AREA THROUGH THIS AFTERNOON.  WHEN
   COUPLED WITH 40-45 KT OF DEEP NNELY SHEAR...ENVIRONMENT WILL SUPPORT
   SMALL SUPERCELLS AND LINE SEGMENTS CAPABLE OF SEVERE HAIL AND
   DAMAGING WIND GUSTS.  DESPITE RATHER WEAK AMBIENT LOW-LEVEL
   SHEAR...THE PRESENCE OF DIFFERENTIAL HEATING BOUNDARIES/WIND SHIFTS
   MAY SERVE TO ENHANCE THE POTENTIAL FOR A TORNADO OR TWO.
   
   FOR ADDITIONAL NEAR TERM GUIDANCE...SEE MCD 801.
   
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