DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT TUE APR 19 2011
VALID 191630Z - 201200Z
...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT OVER
PARTS OF ERN OK...AR...CNTRL/SRN MO...WRN TN...KY...IL...IND AND WRN
OH...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER GREAT LAKES SWWD
INTO SRN TX...
...OUTBREAK OF SEVERE THUNDERSTORMS CAPABLE OF WIDESPREAD
HAIL...DAMAGING WINDS AND A FEW STRONG TORNADOES POSSIBLE THIS
AFTERNOON THROUGH TONIGHT...
...OH VALLEY/LOWER GREAT LAKES SWWD INTO ERN OK/AR...
SHORTWAVE TROUGH OBSERVED OVER THE CNTRL/SRN HIGH PLAINS THIS
MORNING WILL CONTINUE NEWD...CONTRIBUTING TO A CORRIDOR OF 30-60 M
HEIGHT FALLS PER 12-HR AT 500 MB FROM THE CNTRL PLAINS THROUGH THE
MID MS VALLEY INTO UPPER GREAT LAKES. IN THE LOW-LEVELS...SURFACE
LOW ATTENDANT TO THIS SYSTEM ANALYZED OVER W-CNTRL MO AS OF 16Z WILL
DEVELOP NNEWD TO N OF STL BY 19/21Z...THE IL/IND BORDER NEAR DNV BY
20/03Z TO LAKE ERIE BY 20/12Z. A WARM FRONT WILL PRECEDE THE
LOW...GRADUALLY LIFTING NWD THROUGH IL/IND/OH/PA. TRAILING COLD
FRONT WILL ADVANCE SEWD...LIKELY EXTENDING FROM SURFACE LOW OVER
CNTRL IL SWWD THROUGH E-CNTRL MO...NWRN AR AND SERN OK BY 20/00Z.
THIS COLD FRONT WILL SERVE AS THE PRIMARY FOCUS FOR SEVERE
THUNDERSTORM DEVELOPMENT THIS AFTERNOON INTO TONIGHT.
12Z REGIONAL SOUNDINGS SHOWED THE PRESENCE OF STEEP MIDLEVEL LAPSE
RATES/EML IN PLACE FROM THE CNTRL/SRN PLAINS EWD THROUGH THE
MID/LOWER MS VALLEYS. THESE LAPSE RATES RESIDE ABOVE A MOIST AND
RATHER BROAD WARM SECTOR CHARACTERIZED BY PW VALUES OF 1.0-1.5
INCHES AND BOUNDARY LAYER DEWPOINTS IN THE 60S. ASIDE FROM ISOLATED
OCCURRENCES OF HAIL N OF WARM FRONT OVER THE OH VALLEY TODAY...A CAP
AT THE BASE OF THE EML IS EXPECTED TO DELAY SURFACE-BASED TSTM
DEVELOPMENT UNTIL THIS AFTERNOON.
ABUNDANT SUNSHINE...THE STEEP LAPSE RATES AND INCREASING LOW-LEVEL
MOISTURE WILL YIELD A MODERATELY TO STRONG UNSTABLE WARM SECTOR
TODAY WITH MLCAPE VALUES RANGING FROM 1000-2000 J/KG S OF THE WARM
FRONT IN THE OH VALLEY...TO 3000-4000+ J/KG AHEAD OF COLD FRONT FROM
SRN MO INTO ERN OK/WRN AR. FRONTAL UPLIFT COUPLED WITH INCREASED
FORCING FOR ASCENT ATTENDANT TO MIDLEVEL TROUGH ARE EXPECTED TO
FOSTER TSTM DEVELOPMENT BY MID AFTERNOON FROM THE VICINITY OF THE
SURFACE LOW OVER CNTRL/E-CNTRL MO SWWD TO ERN OK/WRN AR.
AN ISALLOBARICALLY BACKED WIND FIELD AHEAD OF SURFACE LOW WILL
RESULT IN A CORRIDOR OF ENHANCED LOW-LEVEL SHEAR FROM E-CNTRL MO EWD
THROUGH CNTRL PARTS OF IL/IND. GIVEN MORE DISCRETE STORM MODES
/I.E. SUPERCELLS/...THIS AREA WILL REPRESENT THE GREATEST RISK FOR
TORNADOES /SOME POSSIBLY STRONG/ FROM LATE THIS AFTERNOON INTO
TONIGHT. OTHERWISE...EXPECT THE DEVELOPMENT OF SUPERCELLS AND LINE
SEGMENTS ALONG COLD FRONT WITH EVENTUAL UPSCALE GROWTH INTO ONE OR
MULTIPLE MCSS/QLCSS. WIDESPREAD OCCURRENCES OF HAIL AND DAMAGING
WINDS /SOME SIGNIFICANT/ ARE EXPECTED ACROSS THE MODERATE RISK AREA
INTO EARLY WEDNESDAY DUE TO THE PRESENCE OF STEEP LAPSE RATES AND
THE WIDE...UNSTABLE WARM SECTOR.
...TX...
TSTM POTENTIAL AND ATTENDANT SEVERE WEATHER THREAT IS MORE UNCERTAIN
WITH SWD EXTENT ALONG THE DRYLINE THIS AFTERNOON OWING TO WEAK OR
NEGLIGIBLE LARGE-SCALE FORCING FOR ASCENT. NONETHELESS...MORNING
VISIBLE SATELLITE IMAGERY DOES SUGGEST THAT STRONG DIABATIC HEATING
WILL OCCUR TODAY ALONG AND W OF DRYLINE...BOOSTING SURFACE
TEMPERATURES INTO THE 90S. SHOULD SUFFICIENT HEATING/CONVERGENCE
DEVELOP TO INITIATE ISOLATED STORMS...THE PRESENCE OF MLCAPE VALUES
OF 3000-4000+ J/KG AND 30-40 KT OF DEEP WLY SHEAR WILL BE SUPPORTIVE
OF SUPERCELLS CAPABLE OF LARGE HAIL. ANY STORMS THAT MAY DEVELOP
WOULD LIKELY WEAKEN BY LATE EVENING AS THE BOUNDARY LAYER BEGINS TO
COOL AND CONVECTIVE INHIBITION INCREASES.
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