SWODY2
SPC AC 271728
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT WED MAY 27 2009
VALID 281200Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS THU AFTN/EVE ACROSS PARTS OF
ALABAMA AND GEORGIA...
...THERE IS A SLGT RISK OF SVR TSTMS THU ACROSS PARTS OF DEEP SOUTH
TEXAS...
...SYNOPSIS...
MODELS INDICATE THAT AN AMPLIFYING UPPER TROUGH OVER THE EASTERN
PACIFIC WILL GRADUALLY SPLIT. WITHIN THE SOUTHERN PORTION...A
CLOSED LOW IS PROGGED TO FORM...BUT REMAIN WELL WEST OF THE PACIFIC
COAST THROUGH THIS PERIOD...THOUGH A BROAD DOWNSTREAM CIRCULATION
WITHIN THE WEAK SUBTROPICAL STREAM MAY APPROACH NORTHERN
BAJA/SOUTHERN CALIFORNIA. AT THE SAME TIME...A CLOSED
LOW/ASSOCIATED SHORT WAVE TROUGH...COMPRISING THE NORTHERN
PORTION...APPEAR LIKELY TO LIFT TOWARD THE BRITISH COLUMBIA COAST.
THIS MAY CONTRIBUTE TO DOWNSTREAM AMPLIFICATION WITHIN THE MAIN BELT
OF POLAR WESTERLIES NEAR THE CANADIAN/U.S. BORDER. AS AN EMBEDDED
SHORT WAVE TROUGH DIGS TO THE SOUTH OF A VORTEX NEAR HUDSON BAY...A
REMNANT LOWER/MID TROPOSPHERIC CYCLONE IS PROGGED TO MIGRATE EAST
NORTHEAST OF THE LOWER GREAT LAKES REGION THROUGH THE ST. LAWRENCE
VALLEY. IN ITS WAKE...WEAK UPPER TROUGHING WILL LINGER OVER MUCH OF
THE EASTERN U.S...DOWNSTREAM OF BROAD UPPER RIDGING ENCOMPASSING
MUCH OF THE INTERMOUNTAIN WEST AND ROCKIES.
ASSOCIATED WITH THIS EVOLVING PATTERN...WEAK INHIBITION IS EXPECTED
TO ALLOW CONSIDERABLE THUNDERSTORM ACTIVITY THURSDAY ACROSS THE GULF
STATES THROUGH MUCH OF THE EASTERN U.S...AS A LINGERING MOIST
BOUNDARY LAYER DESTABILIZES WITH DAYTIME HEATING. AND...GIVEN THE
WARM ENVIRONMENT ACROSS THE HIGHER TERRAIN OF THE WEST...ENOUGH
MOISTURE LIKELY WILL BE PRESENT TO ALSO SUPPORT AT LEAST SCATTERED
THUNDERSTORM ACTIVITY. SEASONABLE INSTABILITY WILL AGAIN CONTRIBUTE
TO SEVERE POTENTIAL IN MOST AREAS WITH A RISK FOR THUNDERSTORMS.
BUT...WITH A COUPLE POSSIBLE EXCEPTIONS...THIS THREAT APPEARS
MARGINAL...OR LIKELY TO REMAIN HIGHLY LOCALIZED WITH LOW
PREDICTABILITY THIS FAR IN ADVANCE.
...AL/GA...PERHAPS PARTS OF WRN FL PANHANDLE...
NCEP SREF INDICATES MODERATE TO STRONG DESTABILIZATION IS POSSIBLE
IN A PRE-FRONTAL CORRIDOR ACROSS ALABAMA BY LATE THURSDAY AFTERNOON.
STRONG HEATING OF A MOIST BOUNDARY LAYER CHARACTERIZED BY SURFACE
DEW POINTS NEAR 70F...BENEATH RELATIVELY STEEP MID-LEVEL LAPSE
RATES...APPEARS LIKELY TO CONTRIBUTE TO CAPE OF 2000-3000 J/KG.
POTENTIAL INSTABILITY COUPLED WITH SIZABLE LOWER/MID TROPOSPHERIC
DEW POINTS SPREADS SHOULD BE SUFFICIENT FOR A FEW SEVERE STORMS
CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING SURFACE WIND GUSTS.
THERE ARE INDICATIONS THAT THIS COULD BE ENHANCED BY SHEAR/FORCING
ASSOCIATED WITH A 30+ KT MID-LEVEL SPEED MAXIMUM...SUPPORTIVE OF AT
LEAST SHORT-LIVED MID-LEVEL UPDRAFT ROTATION. PRIMARY ACTIVITY IS
EXPECTED TO DEVELOP IN THE LOW-LEVEL WARM ADVECTION REGIME EAST OF
THE PRE-FRONTAL THERMAL RIDGE AXIS...ACROSS CENTRAL/EASTERN ALABAMA
...BEFORE SPREADING INTO GEORGIA DURING THE LATE AFTERNOON/EVENING
HOURS.
...DEEP SOUTH TEXAS...
MODERATE TO STRONG INSTABILITY IS EXPECTED TO LINGER IN THE
CONTINUING PRESENCE OF STEEP MID-LEVEL LAPSE RATES ACROSS THE LOWER
RIO GRANDE VALLEY...WHERE MID-LEVEL INHIBITION APPEARS LIKELY TO
REMAIN RELATIVELY WEAK AS WELL. THERE ARE INDICATIONS IN MODEL
GUIDANCE THAT FORCING ASSOCIATED WITH A WAVE WITHIN THE SUBTROPICAL
STREAM COULD CONTRIBUTE TO STORM DEVELOPMENT OFF THE HIGHER TERRAIN
OF MEXICO BY MIDDAY THURSDAY...BEFORE SPREADING ACROSS SOUTHERN
TEXAS COASTAL AREAS BY EARLY THURSDAY EVENING. LOW-LEVEL FLOW
FIELDS ARE PROGGED TO BE WEAK...BUT AN EASTERLY COMPONENT BENEATH
MODEST WESTERLY MID/UPPER FLOW MAY PROVIDE SUFFICIENT SHEAR FOR
ISOLATED SUPERCELLS.
..KERR.. 05/27/2009
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