DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 131727
SWODY2
SPC AC 131725

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1225 PM CDT SAT APR 13 2013

VALID 141200Z - 151200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SRN KS/NRN
OK...

...SYNOPSIS...
LARGE-SCALE UPPER TROUGHING IS FORECAST TO CONTINUE EXPANDING ACROSS
THE WRN U.S. ON SUNDAY...AS A LOW SHIFTS ACROSS THE NRN PLAINS AND A
SECOND BATCH OF ENERGY DIGS SSWWD ALONG THE WRN NOAM COAST INTO THE
PAC NW.

DOWNSTREAM OF THIS LARGE/DEVELOPING TROUGH...A WEAKER SRN STREAM
TROUGH CROSSING THE S CENTRAL U.S. IS PROGGED TO SHIFT ACROSS THE
GULF COAST STATES/SERN U.S. THROUGH THE PERIOD. WIDESPREAD
PRECIPITATION DRIVEN BY STRONG QG FORCING AHEAD OF THIS SYSTEM
SHOULD MAINTAIN A BAROCLINIC ZONE NEAR THE GULF COAST -- THUS
LIMITING DESTABILIZATION/SEVERE POTENTIAL ACROSS MOST OF THE SERN
CONUS.

FARTHER W...A COLD FRONT WILL ADVANCE SEWD ACROSS THE CENTRAL U.S.
WITH TIME...AS THE AFOREMENTIONED NRN PLAINS UPPER LOW PROGRESSES
ENEWD. THIS FRONT WILL FOCUS SHOWERS AND THUNDERSTORMS...AND
LIMITED SEVERE POTENTIAL DURING THE AFTERNOON AND EARLY EVENING
HOURS.

...PARTS OF SRN KS/NRN OK...
WHILE SLY BOUNDARY LAYER FLOW IN RESPONSE TO HIGH PLAINS
CYCLOGENESIS WILL ALLOW AN INCREASE IN LOW-LEVEL MOISTURE ACROSS THE
SRN PLAINS...A CAPPING INVERSION IS FORECAST TO PERSIST -- LIKELY
RESULTING IN LOW-LEVEL CLOUD COVER IN MANY AREAS INTO THE AFTERNOON.
AS A COLD FRONT PROGRESSES SEWD ACROSS IA/MO/KS AND INTO NRN
OK...INCREASING ASCENT WILL AID IN WEAKENING OF THE CAP...AND
EVENTUALLY CONVECTIVE DEVELOPMENT IS EXPECTED FROM SRN WI/IA SWWD TO
ERN KS. DESPITE FAVORABLE SHEAR...VERY MODEST INSTABILITY ACROSS
THIS PORTION OF THE AREA SUGGESTS ONLY A LOW-PROBABILITY THREAT FOR
HAIL/WIND WITH THE STRONGEST CELLS.

GREATER LOW-LEVEL MOISTURE/INSTABILITY WILL EXIST FARTHER S ACROSS
SRN KS/OK -- BUT AGAIN...DEGREE OF CAPE WILL BE MODULATED BY
POTENTIAL FOR LINGERING LOW CLOUD COVER AS MOISTURE STREAMS NWD
BENEATH SUBSTANTIAL LOW-LEVEL CAPPING. IF CLOUDINESS ERODES
SUFFICIENTLY TO PERMIT GRADUAL CAP WEAKENING/DESTABILIZATION --
FRONTAL ASCENT SHOULD THEN ALLOW AMPLE ADDITIONAL CAP EROSION FOR
ISOLATED/LATE AFTERNOON STORM DEVELOPMENT.

WITH 50 KT MID-LEVEL WLYS ATOP THE LOW-LEVEL SLY FLOW...SHEAR WILL
BE SUFFICIENT FOR UPDRAFT ROTATION...AND ATTENDANT THREATS FOR
DAMAGING WINDS AND HAIL -- AND POSSIBLY AN ISOLATED TORNADO.
HOWEVER...WITH THE NUMBER OF STORMS INTO SRN KS/NRN OK LIKELY TO
REMAIN LIMITED AND WITH EVENING COOLING LIKELY TO LIMIT THE THREAT
TEMPORALLY...WILL MAINTAIN ONLY A SMALL 15%/SLIGHT RISK AREA ATTM.

...SRN GA/FL AND VICINITY...
UNCERTAINTY PERSISTS ACROSS THE SERN U.S. THIS FORECAST AS POTENTIAL
FOR/DEGREE OF INLAND PENETRATION OF HIGHER THETA-E AIR REMAINS
DIFFICULT TO DISCERN. THE LATEST NAM RUN DEVELOPS A WEAK SURFACE
LOW INVOF MOB DURING THE AFTERNOON...WHICH THEN SHIFTS NWD ACROSS AL
TO WRN TN LATE IN THE PERIOD. UNDER THIS SCENARIO...WITH BOUNDARY
LAYER FLOW TURNING SLY ACROSS ERN AL/GA/FL...SURFACE-BASED
CONVECTION -- AND ISOLATED TORNADO POTENTIAL -- WOULD SPREAD NWD
ACROSS AT LEAST SERN AL/SRN GA AND THE FL PANHANDLE THROUGH THE
EVENING/OVERNIGHT. HOWEVER...THE GFS DOES NOT DEPICT THIS
CYCLOGENESIS...WITH THE SURFACE WARM FRONT REMAINING NEAR OR S OF
THE FL PANHANDLE AND EVENTUAL CYCLOGENESIS TO OCCUR LATE IN PERIOD
OFF THE GA/SC COAST.

ATTM...IT APPEARS THAT A GFS-TYPE SCENARIO IS MORE PROBABLE...AS
WIDESPREAD ONSHORE/ELEVATED CONVECTION IS EXPECTED TO BE ONGOING
EARLY ACROSS THE GULF COAST REGION IN RESPONSE TO STRONG LOW-LEVEL
WARM ADVECTION. WITH THIS PRECIPITATION EXPECTED TO
CONTINUE/ADVANCE EWD WITH TIME ACROSS THE NRN GULF AND GULF COAST
STATES...SWD SUPPRESSION OF THE WARM FRONT SEEMS CONSISTENT. THUS
-- WHILE NUDGING 5% SEVERE PROBABILITY NWD ACROSS SRN GA TO REFLECT
LOW-PROBABILITY POTENTIAL FOR FARTHER NWD ADVANCE OF THE HIGH
THETA-E GULF BOUNDARY LAYER -- IT APPEARS ATTM THAT LITTLE SEVERE
THREAT WILL EXIST AWAY FROM THE COAST.

FARTHER E ACROSS THE FL PENINSULA...GREATER AFTERNOON
HEATING/DESTABILIZATION WILL OCCUR...BUT LARGE-SCALE ASCENT APPEARS
LIKELY TO REMAIN W OF THE REGION UNTIL AFTER SUNSET. THUS...DEGREE
OF AFTERNOON CONVECTIVE COVERAGE SHOULD REMAIN SOMEWHAT LIMITED --
LIKELY TIED TO SEA-BREEZE CIRCULATIONS. WITH DEEP-LAYER SHEAR
SUPPORTIVE OF ORGANIZED STORMS...LOW-PROBABILITY SEVERE THREAT
REMAINS JUSTIFIED FOR ISOLATED AFTERNOON STORMS...BUT WILL REFRAIN
FROM ANY PROBABILITY UPGRADE ATTM UNTIL DEGREE OF AFTERNOON
CONVECTIVE COVERAGE BECOMES MORE CERTAIN.

..GOSS.. 04/13/2013

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