SWODY2
SPC AC 210527
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1227 AM CDT SUN OCT 21 2007
VALID 221200Z - 231200Z
..THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF LA...MS...AL...
..SYNOPSIS...
HIGHLY AMPLIFIED FLOW REGIME WILL CONTINUE ACROSS THE CONUS INTO THE
BEGINNING OF THE WEEK AS A DEEP MID/UPPER LEVEL TROUGH BECOMES
ESTABLISHED ACROSS THE CENTER OF THE NATION AND BROAD RIDGE AXES
DOMINATE THE ERN AND WRN SEABOARDS. THE LARGE SCALE EVOLUTION OF THE
UPPER TROUGH BECOMES HIGHLY UNCERTAIN AFTER ABOUT MID-WAY THROUGH
THIS FORECAST PERIOD...MONDAY NIGHT INTO EARLY TUESDAY...WITH A WIDE
SPREAD OF POSSIBLE SOLUTIONS DEPICTED IN LATEST DETERMINISTIC AND
ENSEMBLE GUIDANCE. NAM-WRF IS MOST PROGRESSIVE WITH THE TROUGH
DURING THIS TIME WITH THE TROUGH AXIS ESSENTIALLY ALIGNED WITH THE
MS VALLEY BY TUESDAY MORNING. NAM-WRF HAS BEEN TRENDING SLOWER OVER
THE PAST FEW RUNS. LATEST GFS KEEPS THE TROUGH AXIS WEST OF THE MS
VALLEY WITH A MID LEVEL LOW BEGINNING TO CLOSE OFF IN THE BASE OF
THE TROUGH OVER AR. ALL RSM AND WRF MEMBERS OF THE 21Z SREF WOULD
FAVOR THE SLOWER/POSITIVE-TILT CLOSED LOW SOLUTION OVER THE MORE
PROGRESSIVE NEUTRAL-TILT NAM-WRF/ETA SOLUTIONS.
DESPITE THESE DIFFERENCES...CONFLUENT LOW LEVEL SLY FLOW IS FORECAST
TO DEVELOP DOWNSTREAM FROM THE HIGHLY AMPLIFIED TROUGH...FROM THE
LOWER MS VALLEY EWD ACROSS THE NRN GULF COAST AND SOUTHEAST. A
DISTURBANCE...CURRENTLY OFF THE WEST COAST OF FL...IS FORECAST TO
SPREAD NWWD AND INLAND ACROSS THE FL PNHDL THROUGH LATE IN THE DAY
ONE PERIOD. THIS FEATURE SHOULD PRODUCE AN INCREASE IN CLOUDS AND
TSTMS ACROSS MUCH OF THE REGION AHEAD OF THE SLOW MOVING COLD FRONT
ASSOCIATED WITH THE UPPER TROUGH. A NARROW ZONE OF ENHANCED SEVERE
STORM POTENTIAL MAY EVOLVE ACROSS PARTS OF THE MS DELTA/MS/AL AREAS
AS TSTMS PERSIST IN THIS REGION AND LARGE SCALE ASCENT AND SHEAR
GRADUALLY STRENGTHEN WITH THE EWD MOVING TROUGH/FRONT.
..LA/MS/AL...
THROUGH MONDAY AFTERNOON...LATEST NAM...GFS...AND SREF MEANS ARE IN
REMARKABLY GOOD AGREEMENT INDICATING A SW-NE ORIENTED ZONE OF STRONG
ASCENT AND HIGH QPF EXTENDING FROM THE NW GULF/MS DELTA NEWD TO THE
TN VALLEY. INSTABILITY WITHIN THIS CORRIDOR OF STRENGTHENING WARM
ADVECTION AHEAD OF THE FRONT WILL LIKELY REMAIN MEAGER DUE TO MOIST
ADIABATIC LAPSE RATES. GREATER DESTABILIZATION WILL BE POSSIBLE
ALONG THE IMMEDIATE GULF COAST IN CLOSER PROXIMITY TO WARM SEA
SURFACE TEMPS IN THE 80S. MID LEVEL WINDS AND RESULTANT EFFECTIVE
SHEAR ARE FORECAST TO INCREASE DURING THE AFTERNOON WHEN ANY LOCAL
DESTABILIZATION MAY BE ADEQUATE FOR SURFACE-BASED CONVECTION.
EFFECTIVE INFLOW LAYER SRH AND LOW LFC DEPICTED IN NAM-WRF AND
NAM-KF FORECAST SOUNDINGS APPEAR SUFFICIENT TO SUSTAIN LOW LEVEL
STORM ROTATION. PATTERN AND MODEL QPF SIGNALS DEPICT SLOW-MOVING
QLCS DEVELOPMENT OCCURRING AHEAD OF THE ADVANCING FRONT. HOWEVER...A
FEW STRONGER STORMS EMBEDDED WITHIN THIS SYSTEM MAY OCCASIONALLY
EXHIBIT GREATER ORGANIZATION/PERSISTENCE WITH SCATTERED WIND DAMAGE
AND/OR A COUPLE OF TORNADOES POSSIBLE INTO MONDAY EVENING.
.CARBIN.. 10/21/2007
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