SWODY1
SPC AC 070558
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT WED OCT 07 2009
VALID 071200Z - 081200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
LARGE SCALE SPLIT FLOW REGIME WILL CONTINUE TO PREVAIL OVER THE
WESTERN STATES...WITH THE SOUTHERN STREAM UPPER LOW OVER SOUTHERN CA
EXPECTED TO MIGRATE EASTWARD OVER THE SOUTHWEST DESERTS/NORTHWEST
MEXICO THROUGH THE PERIOD. IN THE EAST...A SWIFT MOVING UPPER TROUGH
WILL CONTINUE TO STEADILY PROGRESS EAST-NORTHEASTWARD OVER THE
NORTHEAST STATES/NEW ENGLAND...WHILE A SUBTROPICAL RIDGE BUILDS OVER
FL AND THE ADJACENT SOUTHEAST STATES. PRIMARY SURFACE COLD FRONT
WILL QUICKLY RACE EASTWARD OFF MUCH OF THE ATLANTIC SEABOARD BY
AFTERNOON...WHILE THE WEST-SOUTHWEST PORTION OF THE FRONT
STALLS/ELONGATES GENERALLY EAST-WEST ACROSS THE GULF COAST STATES TO
TX.
...WEST/SOUTHWEST TX AND SOUTHEAST NM...
STALLED FRONTAL ZONE WILL REMAIN ALONG THE HIGHER TERRAIN OF FAR
SOUTHWEST TX...AND BEGIN TO RETURN NORTHWARD DURING THE LATTER HALF
OF THE PERIOD COINCIDENT WITH THE INITIAL ONSET OF MODEST LARGE
SCALE HEIGHT FALLS FROM NM INTO WEST TX /VIA THE SOUTHWEST STATES
UPPER TROUGH/. A MOIST AIRMASS/WEAK INHIBITION AND FRONTAL
CONVERGENCE/DIFFERENTIAL HEATING ALONG THE HIGHER TERRAIN SHOULD
LEAD TO ISOLATED TO POSSIBLY SCATTERED SURFACE BASED TSTMS ACROSS
PORTIONS OF SOUTHWEST TX/SOUTHEAST NM BY LATE AFTERNOON/EARLY
EVENING. A RELATIVELY MOIST AIRMASS/MODERATE INSTABILITY COUPLED
WITH GRADUALLY INCREASING SOUTHWESTERLY FLOW ALOFT /35-50 KT/ MAY
SUPPORT SOME SUSTAINED MULTICELLS/SUPERCELLS CAPABLE OF MAINLY
SEVERE HAIL. SUBSEQUENT/INCREASING DEVELOPMENT INTO FAR WEST TX
APPEARS LIKELY THROUGH THE EVENING/OVERNIGHT...WITH AT LEAST SOME
SEVERE THREAT /MAINLY HAIL/ REMAINING POSSIBLE.
...SOUTHERN HIGH PLAINS OF TX TO OK/LOWER MO VALLEY TONIGHT...
A STRENGTHENING NOCTURNAL LOW LEVEL JET /40-50 KT/ ACROSS THE
SOUTHERN PLAINS...AND ONSET OF LATE PERIOD HEIGHT FALLS...WILL
CONTRIBUTE TO THE NORTHEASTWARD TRANSPORT OF A MOIST/UNSTABLE
ELEVATED AIRMASS ATOP A COOL/STABLE NEAR-SURFACE LAYER LATE TONIGHT.
ACCORDINGLY...00Z DETERMINISTIC GUIDANCE/MAJORITY OF 21Z SREF
MEMBERS IMPLY AN INCREASE OF ELEVATED TSTMS TOWARD/AFTER 06Z FROM
PORTIONS OF WEST TX/OK TO THE LOWER MO VALLEY/OZARKS. WITH AN
UNSTABLE SOURCE REGION AIRMASS INITIALLY ACROSS THE SOUTH HALF OF
TX...WEAK TO MODERATE ELEVATED BUOYANCY /500-1500 J PER KG/ AND
AMPLE SHEAR THROUGH THE CLOUD BEARING LAYER IS SUGGESTIVE OF AT
LEAST ISOLATED BOUTS OF SEVERE HAIL INTO THE OVERNIGHT.
...COASTAL CAROLINAS/GA...
WHILE MORNING CLOUD COVER/PRECIPITATION AHEAD OF THE APPROACHING
COLD FRONT MAY TEND TO LIMIT THE DEGREE OF DESTABILIZATION...IT
APPEARS THAT A MOIST/POTENTIALLY UNSTABLE AIRMASS MAY LINGER ACROSS
THE COASTAL CAROLINAS/GA THROUGH MUCH OF THE AFTERNOON/PEAK HEATING
AHEAD OF THE FRONT. AS SUCH...BENEATH MODERATELY STRONG WESTERLY MID
LEVEL FLOW...AN ISOLATED/MARGINAL SEVERE RISK APPEARS WARRANTED
ACROSS PORTIONS OF THE COASTAL CAROLINAS/GA PRIOR TO THE COLD FRONT
CLEARING THE COAST.
...NY/NEW ENGLAND...
PROGRESSIVE MID LEVEL TROUGH WITH AN ATTENDANT STRONG DEEP LAYER
WIND FIELD AND FAST MOVING COLD FRONT WILL CROSS PORTIONS OF NY/NEW
ENGLAND DURING THE DAY. ONE OR MORE BANDS OF LOW-TOPPED CONVECTION
SHOULD BE ONGOING EARLY IN THE DAY ALONG/AHEAD OF THE COLD FRONT.
GIVEN SUFFICIENT /ALBEIT MODEST/ DIURNAL HEATING AHEAD OF THE COLD
FRONT IN THE PRESENCE OF STRONG DEEP LAYER WIND FIELDS...UPDRAFTS OF
SUFFICIENT DEPTH WITH A FEW HUNDRED J/KG OF SBCAPE MAY RESULT IN A
FAST MOVING/LOW TOPPED THUNDERY CONVECTIVE LINE CAPABLE OF ENHANCED
WIND GUSTS/PERHAPS HAIL TO SEVERE LEVELS.
..GUYER/GARNER.. 10/07/2009
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