SWODY2
SPC AC 170611
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1211 AM CST TUE FEB 17 2009
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE SERN
STATES INTO SRN PORTION OF THE OH VALLEY...
...SYNOPSIS...
SRN BRANCH UPPER JET WILL ADVANCE INTO THE LOWER MS...TN AND OH
VALLEYS WED AND INTENSIFY AS IT MERGES WITH AMPLIFYING NRN STREAM.
SUBSEQUENT CONSOLIDATION AND AMPLIFICATION OF THE TROUGH WILL
CONTINUE OVER THE ERN STATES WED NIGHT. SURFACE LOW WILL SHIFT NEWD
THROUGH NRN PORTIONS OF THE OH VALLEY AND SRN GREAT LAKES WITHIN
EXIT REGION OF UPPER JET. TRAILING COLD FRONT WILL SWEEP EWD THROUGH
THE OH VALLEY AND SERN STATES.
...SERN STATES...
GULF FRONTAL INTRUSION THAT OCCURRED MONDAY HAD A GREATER IMPACT
OVER THE CNTRL AND ERN GULF...AND LATEST OBSERVATIONAL DATA INDICATE
UPPER 60S DEWPOINTS OVER THE WRN GULF JUST OFFSHORE OF S TX. AN AXIS
OF PARTIALLY MODIFIED GULF AIR WILL ADVECT NEWD THROUGH THE LOWER MS
VALLEY AND A PORTION OF THE SERN STATES ALONG A STRONG SWLY LOW
LEVEL JET ASSOCIATED WITH THE EWD MIGRATING CYCLONE. ELEVATED STORMS
WILL BE ONGOING OVER A PORTION OF THE SERN U.S. AND OH VALLEY WITHIN
ZONE OF STRONG ISENTROPIC ASCENT. SOME OF THE EARLY ACTIVITY OVER
THE SERN STATES MAY BE CAPABLE OF PRODUCING HAIL. THE STORMS WILL
SHIFT EAST DURING THE DAY...BUT IN THEIR WAKE...WIDESPREAD CLOUDS
WILL LIKELY PERSIST OVER MUCH OF WARM SECTOR WHICH WILL TEND TO
LIMIT INSTABILITY. VEERING OF THE LOW LEVEL FLOW TO WLY DURING THE
DAY MAY HELP TO MIX OUT THE LOW CLOUDS FROM THE WEST JUST AHEAD OF
THE FRONT.
THE VEERING BOUNDARY LAYER FLOW EAST OF FRONT AND TENDENCY FOR THE
LOW LEVEL JET TO SHIFT EWD WITH TIME WILL TEND TO LIMIT DEEP
CONVERGENCE IN VICINITY OF THE FRONT. MODEL SOUNDINGS ALSO APPEAR TO
BE INFLUENCED BY MID-LEVEL SUBSIDENCE IN WRN PORTIONS THE OF
PRE-FRONTAL WARM SECTOR DURING THE AFTERNOON. THESE FACTORS LEND
SOME UNCERTAINTY REGARDING AMOUNT OF FRONTAL CONVECTIVE
REDEVELOPMENT. NEVERTHELESS...POTENTIAL WILL EXIST FOR ADDITIONAL
STORMS TO DEVELOP ALONG EWD ADVANCING FRONT WITHIN ZONE OF HEIGHT
FALLS AND LOW LEVEL CONFLUENT FLOW REGIME FROM THE LOWER MS VALLEY
INTO PARTS OF THE SERN STATES. STRONG WSWLY LOW-LEVEL FLOW IMPINGING
ON BOUNDARIES ASSOCIATED WITH THE EWD MIGRATING MCS MAY ALSO
CONTRIBUTE TO NEW CONVECTIVE DEVELOPMENT.
ACTIVITY WILL BE EMBEDDED WITHIN VERY STRONG KINEMATIC PROFILES
WHICH WOULD SUPPORT AN ORGANIZED SEVERE THREAT INCLUDING SUPERCELLS
AND BOWING STRUCTURES WITH ANY SURFACE BASED DEEP CONVECTION.
LINGERING UNCERTAINTY REGARDING MESOSCALE DETAILS AND LIMITING
FACTORS IMPOSED BY LIKELIHOOD OF A MARGINAL THERMODYNAMIC
ENVIRONMENT PRECLUDE INTRODUCING HIGHER END PROBABILITIES AT THIS
TIME.
...SRN PORTIONS OF THE OH VALLEY...
COLDER AIR ALOFT AND PLUME OF STEEPER MID LEVEL LAPSE RATES WILL
ACCOMPANY THE UPPER JET EXIT REGION THROUGH SRN PARTS OF THE OH
VALLEY...AND THIS COULD COMPENSATE FOR MORE LIMITED LOW LEVEL
MOISTURE IN THIS AREA. HOWEVER...INSTABILITY WILL REMAIN VERY
MARGINAL IN THIS REGION. STRONG AGEOSTROPHIC FORCING ATTENDING THE
UPPER JET WILL LIKELY CONTRIBUTE TO REDEVELOPMENT OF LOW TOPPED
CONVECTION SOUTH AND EAST OF SURFACE LOW TRACK AND ALONG TRAILING
COLD FRONT. THE DEEP WLY FLOW MAY RESULT IN LOW CLOUDS MIXING OUT
FROM THE WEST WITHIN DRY-SLOT REGION WHICH WOULD AID BOUNDARY LAYER
DESTABILIZATION. IF SUFFICIENT INSTABILITY DEVELOPS...STRONG
VERTICAL SHEAR AND STEEP LAPSE RATES WOULD SUPPORT A THREAT OF LOW
TOPPED SUPERCELLS AND BOWING SEGMENTS.
..DIAL.. 02/17/2009
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