SWODY2
SPC AC 061715
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1215 PM CDT MON OCT 06 2008
VALID 071200Z - 081200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A SPLIT UPPER FLOW PATTERN LINGERS ACROSS MUCH OF CANADA AND THE
U.S...BUT MODELS INDICATE THAT THE EXIT REGION OF A STRONG ZONAL
PACIFIC JET STREAK WILL NOSE INLAND ACROSS THE PACIFIC NORTHWEST
COAST LATE TONIGHT...BEFORE CONTINUING EASTWARD NEAR/JUST SOUTH OF
THE INTERNATIONAL BORDER AREA...INTO THE UPPER MISSISSIPPI VALLEY BY
12Z WEDNESDAY. AS THIS OCCURS...NORTHERN AND SOUTHERN STREAM SHORT
WAVE IMPULSES...NOW SOMEWHAT IN PHASE TO THE LEE OF THE
ROCKIES...ARE FORECAST TO PROGRESS EASTWARD THROUGH THE PERIOD. THE
NORTHERN STREAM IMPULSE IS EXPECTED TO LIFT NORTHWARD TOWARD HUDSON
BAY...WITH THE BLOCKING NORTHERN STREAM RIDGE OVER CENTRAL CANADIAN
BREAKING DOWN...WHILE THE SOUTHERN IMPULSE SHIFTS EASTWARD THROUGH
THE MID/LOWER MISSISSIPPI VALLEY REGION.
...MISSISSIPPI VALLEY/GULF COAST...
VARIABILITY AMONG THE MODELS...AND AMONG NCEP SREF/MREF MEMBERS...IS
QUITE LARGE CONCERNING THE EVOLUTION THE SOUTHERN BRANCH TROUGH.
BUT...GUIDANCE GENERALLY INDICATES ASSOCIATED SURFACE CYCLOGENESIS
FROM THE PLAINS INTO THE MISSISSIPPI VALLEY WILL REMAIN WEAK...WHILE
THE EXPANSIVE SURFACE RIDGE IN THE EAST...ASSOCIATED WITH THE
BLOCKING PATTERN...IS SLOW TO WEAKEN/RETREAT EASTWARD.
THUS...DESPITE THE FACT THAT MODIFICATION OF THE BOUNDARY LAYER OVER
THE GULF OF MEXICO IS NOW FINALLY BEGINNING TO SUPPORT A SUBSTANTIAL
RETURN FLOW OF MOISTURE...THE DEVELOPMENT OF A BROAD WARM SECTOR
ACROSS THE SOUTH CENTRAL STATES APPEARS UNLIKELY TODAY THROUGH
TUESDAY.
BOUNDARY LAYER DESTABILIZATION DURING THE DAY TUESDAY IS EXPECTED TO
BECOME CONFINED TO A NARROWING WEDGE ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY...WHERE CLOUD COVER COULD RESTRICT SURFACE
HEATING. COUPLED WITH THE PROSPECT FOR ONLY MODEST MID-LEVEL
COOLING...AND MODEL PROGS INDICATING THAT STRONGER LOW-LEVEL FLOW
WILL SHIFT NORTH/EAST OF THE REGION EARLY IN THE DAY...SEVERE
POTENTIAL STILL APPEARS UNCERTAIN OR LOW. OF PRIMARY
CONCERN...MID-LEVEL DRYING ON THE WESTERN EDGE OF THE LOW-LEVEL
MOIST AXIS MAY PROVIDE A WINDOW OF OPPORTUNITY FOR SUFFICIENT
DESTABILIZATION OF THE BOUNDARY LAYER...PRIOR TO THE ONSET OF
MID-LEVEL COOLING/LIFT...FOR SCATTERED VIGOROUS STORM DEVELOPMENT
DURING THE LATE AFTERNOON HOURS. IF THIS OCCURS...DEEP LAYER SHEAR
BENEATH CYCLONIC 40 KT 500 MB FLOW PROBABLY WILL BE SUFFICIENT FOR
UPDRAFT ROTATION...AND POTENTIAL FOR AT LEAST SHORT-LIVED SUPERCELLS
CAPABLE OF PRODUCING HAIL/LOCALIZED DAMAGING WIND GUSTS.
..KERR.. 10/06/2008
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