DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 201731
SWODY2
SPC AC 201730

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1130 AM CST WED NOV 20 2013

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THURSDAY AFTERNOON AND
EVENING ACROSS PARTS OF NORTHWEST TEXAS INTO SOUTHWESTERN
OKLAHOMA...

...SYNOPSIS...
MODELS CONTINUE TO INDICATE THAT A COUPLE OF INITIALLY ZONAL BELTS
OF STRONGER MID/UPPER FLOW EMERGING FROM THE CENTRAL PACIFIC WILL
UNDERGO CONSIDERABLE AMPLIFICATION ACROSS THE EASTERN PACIFIC INTO
NORTH AMERICA LATER TODAY THROUGH THURSDAY. WITHIN AN UPPER TROUGH
EVOLVING IN THE SOUTHERN BRANCH...ACROSS THE CALIFORNIA COAST INTO
THE FOUR CORNERS STATES...A SIGNIFICANT CLOSED LOW IS FORECAST TO
FORM NEAR THE SOUTHERN CALIFORNIA COAST DURING THE PERIOD.
DOWNSTREAM...MID/UPPER RIDGING LIKELY WILL CONTINUE TO BUILD ACROSS
THE SOUTH CENTRAL AND SOUTHEASTERN STATES...BUT THIS PROBABLY WILL
BE TEMPERED BY UPPER TROUGH DEEPENING WITHIN THE NORTHERN
BRANCH...ACROSS THE CENTRAL INTERNATIONAL BORDER AREA INTO THE
NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY.

BENEATH THE INCREASINGLY CONFLUENT STREAMS...COLD SURFACE RIDGING IS
EXPECTED TO CONTINUE TO BUILD AND NOSE SOUTHWARD TO THE LEE OF THE
ROCKIES. THE LEADING EDGE OF THIS COLD INTRUSION PROBABLY WILL
REACH WESTERN PORTIONS OF THE LOWER GREAT LAKES...THE MISSISSIPPI
VALLEY AND SOUTHERN PLAINS BY 12Z FRIDAY. AT THE SAME TIME...A
RETURN FLOW OF MOISTURE IS EXPECTED TO PERSIST OFF THE GULF OF
MEXICO...ON THE WESTERN FRINGE OF A SLOWLY WEAKENING/EASTWARD
SHIFTING SURFACE RIDGE NEAR THE ATLANTIC COAST.

...SRN PLAINS INTO MID MS/LWR OH VALLEYS...
MODELS SUGGEST THAT WITHIN THE PLUME OF RETURNING MOISTURE...WEAK TO
MODESTLY STEEP LOWER/MID TROPOSPHERIC LAPSE RATES WILL SUPPORT
SUFFICIENT CAPE FOR THUNDERSTORM DEVELOPMENT...GENERALLY AROUND THE
NORTHERN PERIPHERY OF THE MID/UPPER SUBTROPICAL RIDGE...SUPPORTED BY
LIFT ASSOCIATED WITH LOW/MID-LEVEL WARM ADVECTION. THIS POTENTIAL
IS EXPECTED TO CONTINUE ACROSS PARTS OF THE CENTRAL/SOUTHERN PLAINS
INTO THE MIDDLE MISSISSIPPI VALLEY EVEN ABOVE THE SOUTHWARD
ADVANCING LEADING EDGE OF THE SURFACE COLD INTRUSION.

IT DOES APPEAR THAT...PRIOR TO THE ARRIVAL OF THE FRONT...THE
BOUNDARY LAYER WILL BECOME SEASONABLY MOIST ACROSS MUCH OF CENTRAL
AND EASTERN TEXAS INTO OKLAHOMA BY THURSDAY AFTERNOON. WITH DAYTIME
HEATING...STRONGEST WITHIN A PRE-FRONTAL AXIS ACROSS THE TEXAS SOUTH
PLAINS INTO SOUTHWEST OKLAHOMA...CONDITIONAL AND CONVECTIVE
INSTABILITY PROBABLY WILL BECOME SUFFICIENT TO SUPPORT A RISK FOR
SEVERE STORMS. LARGE-SCALE FORCING TO THE SOUTH OF THE FRONT IS
EXPECTED TO REMAIN WEAK...AND UNCERTAINTY REMAINS CONCERNING THE
RATE OF SOUTHWARD PROGRESSION OF THE COLD FRONT...BUT A WINDOW OF
OPPORTUNITY DOES APPEAR TO EXIST FOR BOUNDARY LAYER STORM
DEVELOPMENT IN A ZONE OF ENHANCED LOW-LEVEL CONVERGENCE NEAR A WEAK
LOW IN THE VICINITY OF WICHITA FALLS BY LATE AFTERNOON. DEEP LAYER
SHEAR WILL BE SUFFICIENT FOR SUPERCELLS...CAPABLE OF PRODUCING AT
LEAST SEVERE HAIL. AND THIS THREAT MAY CONTINUE INTO THE
EVENING...EVEN AS STORMS BECOME UNDERCUT BY THE FRONT...BEFORE THE
SURFACE-BASED COLD AIR DEEPENS FURTHER ACROSS THE RED RIVER
VALLEY...AND THE ENVIRONMENT STABILIZES.

..KERR.. 11/20/2013

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