SWODY1
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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