Thursday, April 09, 2009

Severe Weather Tomorrow - From SPC...





DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1216 PM CDT THU APR 09 2009

VALID 101200Z - 111200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE OH AND TN
VALLEY SWD INTO THE CNTRL/ERN GULF STATES AND EWD INTO THE
CAROLINAS...

..SYNOPSIS

AN AMPLIFIED BUT PROGRESSIVE LARGE-SCALE PATTERN WILL BE MAINTAINED
OVER THE CONUS THROUGH THE DAY TWO PERIOD. THE PRIMARY FEATURE OF
INTEREST WILL BE MID/UPPER-LEVEL LOW WHICH WILL GRADUALLY WEAKEN AND
EVOLVE INTO AN OPEN WAVE WHILE TRANSLATING EWD FROM THE OZARK
PLATEAU AND LOWER MS VALLEY TO THE MID ATLANTIC COAST BY SATURDAY
MORNING. AS THIS PROCESS OCCURS...LATEST MODEL GUIDANCE SUGGESTS
THAT AN UPSTREAM VORTICITY MAXIMUM/JET STREAK WILL ROTATE THROUGH
THE MEAN TROUGH BASE ACROSS THE TN VALLEY INTO VA/NC FRIDAY
AFTERNOON INTO FRIDAY NIGHT. THIS ERN U.S. WAVE WILL PRECEED A MORE
INTENSE TROUGH WHICH WILL EVENTUALLY FORM INTO A CLOSED SYSTEM OVER
THE LOWER CO VALLEY INTO NRN BAJA AND THE GULF OF CA.

IN THE LOW LEVELS...SURFACE CYCLONE NEAR THE CONFLUENCE OF THE MS/OH
RIVERS AT 10/12Z WILL DEVELOP ENEWD ACROSS NRN KY AND SRN
WV...EVENTUALLY REACHING THE DELMARVA BY 11/12Z. ATTENDANT COLD
FRONT WILL PUSH EWD THROUGH THE TN VALLEY AND GULF STATES TO ALONG
THE MID/SERN ATLANTIC COASTS BY SATURDAY MORNING.

...OH/TN VALLEYS INTO THE CNTRL/ERN GULF STATES AND EWD TO THE
CAROLINAS...

EML/STEEP LAPSE RATE PLUME OBSERVED OVER THE SRN PLAINS THIS MORNING
WILL BE ADVECTED EWD INTO THE REGION WITH WSWLY AIRFLOW
REGIME...ALONG SRN THROUGH ERN PERIPHERIES OF MIDLEVEL TROUGH.
WHILE WARM SECTOR BOUNDARY LAYER WILL NOT BE OVERLY MOIST /I.E.
DEWPOINTS IN 50S OVER KY/TN TO LOWER/MID 60S OVER THE GULF
STATES/...THESE STEEP LAPSE RATES COUPLED WITH GENERALLY COOL
MIDLEVEL THERMODYNAMIC PROFILES WILL YIELD MLCAPE APPROACHING
1000-1500 J/KG OVER THE TN VALLEY/CUMBERLAND PLATEAU...TO 1500-2000
J/KG OVER THE CNTRL/ERN GULF STATES.

TSTMS /SOME SEVERE/ ARE EXPECTED TO BE ONGOING FRIDAY MORNING WITHIN
ZONE OF DEEP ASCENT AHEAD OF SURFACE LOW OVER PARTS OF THE LOWER OH
AND LOWER MS VALLEYS...AS WELL AS WITHIN WAA REGIME FARTHER E ACROSS
PARTS OF ERN TN/AL/NRN GA. THE FORMER ACTIVITY WILL LIKELY INCREASE
IN BOTH COVERAGE AND INTENSITY BY LATE MORNING/EARLY AFTERNOON
ALONG/AHEAD OF COLD FRONT FROM CNTRL KY/MIDDLE TN SWD INTO AL AS
STRONGER FORCING/HEIGHT FALLS ASSOCIATED WITH SECONDARY VORTICITY
MAXIMUM ACT ON DESTABILIZING AIR MASS.

GIVEN THE STEEP LAPSE RATES/MODERATE INSTABILITY AND DEEP-LAYER
SHEAR RANGING FROM 30-40 KT INVOF SURFACE LOW OVER KY TO 50-65 KT
INTO MS/AL/GA...ENVIRONMENT WILL BE QUITE SUPPORTIVE OF EMBEDDED
SUPERCELL STRUCTURES CAPABLE OF VERY LARGE HAIL AND DAMAGING WINDS.
CURRENTLY...IT APPEARS THAT THE GREATEST TORNADO THREAT WILL EXIST
ACROSS MIDDLE/ERN TN INTO NRN PARTS OF AL/GA AND PERHAPS AS FAR E AS
WRN SC FRIDAY AFTERNOON INTO EVENING. HERE...REINTENSIFICATION OF A
SWLY LLJ WILL OCCUR IN RESPONSE TO ABOVE-MENTIONED...SECONDARY
VORTICITY MAXIMUM RESULTING IN NOTABLY STRONGER LOW-LEVEL SHEAR
/I.E. 0-1 KM SHEAR APPROACHING 30-35 KT/. SHOULD FUTURE NUMERICAL
GUIDANCE AND OBSERVATIONAL DATA CONTINUE TO SUGGEST A SIMILAR
THREAT...A MODERATE RISK MAY BE REQUIRED IN SUBSEQUENT DAY ONE
OUTLOOKS.


PRE-FRONTAL CLUSTERS/BANDS OF SEVERE STORMS WILL CONTINUE FRIDAY
NIGHT EWD THROUGH THE CNTRL/SRN APPALACHIANS AND PIEDMONT...
EVENTUALLY INTO THE COASTAL PLAINS. WHILE INSTABILITY WILL TEND TO
DIMINISH WITH TIME...A STRONGLY SHEARED KINEMATIC ENVIRONMENT WILL
CONTINUE TO FAVOR EMBEDDED SUPERCELL AND/OR BOWING STRUCTURES WILL
THE THREAT FOR DAMAGING WINDS...HAIL AND PERHAPS TORNADOES.

..MEAD.. 04/09/2009

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