DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 261732
SWODY2
SPC AC 261730

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1230 PM CDT FRI APR 26 2013

VALID 271200Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE LOWER MS VALLEY INTO
E TX...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PART OF THE EDWARDS
PLATEAU AND SOUTH/CENTRAL TX....

...SYNOPSIS...
A SHORTWAVE TROUGH MOVING ACROSS THE SRN PLAINS DAY 1 SHOULD WEAKEN
SOME AS IT TRACKS TOWARD THE LOWER OH AND LOWER MS VALLEYS...WITH
GRADUAL HEIGHT FALLS EXPECTED TO SPREAD ACROSS THE OH/TN VALLEYS...
CENTRAL GULF COAST STATES TO TX. DESPITE A WEAKENING TREND OF
QUASI-ZONAL MIDLEVEL WLYS WITHIN THE SRN PERIPHERY OF THE TROUGH...A
BAND OF 40 KT WIND SPEEDS SHOULD EXTEND FROM FAR W TX THROUGH
CENTRAL TX TO THE NRN EXTENT OF THE CENTRAL GULF COAST STATES AND
SRN APPALACHIANS TO SC.

A SURFACE LOW ATTENDANT TO THE SHORTWAVE TROUGH SHOULD BE LOCATED
INVOF THE OK/AR BORDER AT 12Z SATURDAY...AND TRACK TOWARD THE LOWER
OH VALLEY THIS FORECAST PERIOD. A COLD FRONT TRAILING SWWD FROM THE
LOW WILL SETTLE SWD INTO EAST AND CENTRAL TX...WHILE A WARM FRONT
INITIALLY EXTENDING SEWD THROUGH THE LOWER MS VALLEY MOVE ENEWD
ACROSS THE CENTRAL GULF COAST STATES AND TN VALLEY.

...LOWER MS VALLEY REGION...
ELEVATED STORMS WILL PROBABLY BE ONGOING WITHIN ZONE OF ISENTROPIC
ASCENT ALONG AND NORTH OF WARM FRONT FROM PORTIONS OF AR EWD INTO
THE TN VALLEY. THE WARM SECTOR ACROSS THIS REGION WILL HAVE
PARTIALLY MODIFIED GULF AIR ADVECTED INTO THIS AREA WITH SURFACE
DEWPOINTS IN THE LOW TO MID 60S. POTENTIAL WILL EXIST FOR THE
ATMOSPHERE TO BECOME MODERATELY UNSTABLE /1000-1500 J/KG MLCAPE/ AS
DIABATIC WARMING OF THE BOUNDARY LAYER COMMENCES. ERN EXTENSION OF
THE EML WILL LIKELY HAVE ADVECTED THROUGH WARM SECTOR RESULTING IN
AT LEAST A MODEST CAP. HOWEVER...THE CAP WILL LIKELY WEAKEN AS THE
BOUNDARY LAYER DESTABILIZES AND STORMS MAY DEVELOP ALONG AND AHEAD
OF SEWD ADVANCING COLD FRONT SATURDAY AFTERNOON. MODELS INDICATE
SOME UNCERTAINTY WITH THE WWD EXTENT OF TSTM DEVELOPMENT...BUT THIS
OUTLOOK WILL MAINTAIN THE SLIGHT RISK. LLJ IS FORECAST TO SHIFT INTO
THE TN VALLEY EARLY IN PERIOD IN ASSOCIATION WITH A LEAD VORT MAX
EJECTING THROUGH ERN PERIPHERY OF UPPER TROUGH LEAVING WEAK AND
VEERED LOW LEVEL WINDS IN WARM SECTOR. HOWEVER...THE BELT OF
STRONGER MID-UPPER FLOW WITHIN BASE OF THE TROUGH WILL CONTRIBUTE TO
STRONGER LARGELY UNIDIRECTIONAL 0-6 KM SHEAR. POTENTIAL WILL EXIST
FOR SOME UPDRAFTS TO ROTATE WITH STORM SPLITS ALSO POSSIBLE.
ATTENDANT THREATS FOR HAIL AND DAMAGING WINDS EXIST ACROSS THIS
AREA.

...EDWARDS PLATEAU/S TX INTO CNTRL TX...
CONFIDENCE IS GREATER WITH THE DEVELOPMENT OF TSTMS...AND COVERAGE
THEREOF...ACROSS THE SRN EXTENT OF THE EDWARDS PLATEAU INTO ADJACENT
S TX AS THE SURFACE FRONT SETTLES SWD INTO THIS REGION...AND ALSO
EXPECTED TSTM DEVELOPMENT WITHIN UPSLOPE FLOW REGIME INTO NRN
COAHUILA. THIS IS BASED ON AGREEMENT WITH THE 12Z NAM/GFS AND 00Z
ECMWF...AND WARRANTS AN INCREASE IN SEVERE PROBABILITIES AND THE
INTRODUCTION OF A CATEGORICAL SLIGHT RISK. STEEP EML ALREADY IN
PLACE PER 12Z DRT SOUNDING WILL BE MAINTAINED INTO DAY 2...THOUGH IS
FORECAST TO WEAKEN SATURDAY AFTERNOON GIVEN THE GRADUAL HEIGHT FALLS
AND DIABATIC HEATING IN THE WARM SECTOR. THESE FACTORS WILL ALSO
CONTRIBUTE TO THE DEVELOPMENT OF MODERATE INSTABILITY. ALTHOUGH
FLOW IN THE 0-3 KM LAYER IS FORECAST TO BE VERY WEAK...WSWLY
MIDLEVEL WINDS UP TO 35-40 KT WILL RESULT IN EFFECTIVE BULK SHEAR
AROUND 40 KT SUPPORTIVE OF ORGANIZED STORMS...WITH STRAIGHT
HODOGRAPHS SUGGESTING SPLITTING STORMS WILL BE POSSIBLE. MODERATE
INSTABILITY AND STEEP MIDLEVEL LAPSE RATES WILL FAVOR A THREAT FOR
LARGE HAIL...SOME VERY LARGE...AND DAMAGING WINDS. ACTIVITY SHOULD
TEND TO DEVELOP/SPREAD ENEWD INTO SOUTH CENTRAL TX INVOF THE
FRONT...WITH SEVERE THREAT PERSISTING INTO THE EVENING UNTIL
BOUNDARY LAYER COOLING INCREASES SURFACE BASED INHIBITION.

..PETERS.. 04/26/2013

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