SWODY1
SPC AC 181631
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1131 AM CDT WED MAY 18 2011
VALID 181630Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE CNTRL AND
SRN HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER OH
VALLEY INTO MID ATLANTIC STATES...
...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.
..MEAD/ROGERS.. 05/18/2011
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