DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 301221
SWODY1
SPC AC 301219

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0719 AM CDT SUN SEP 30 2012

VALID 301300Z - 011200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR THE LWR MS VALLEY AND CNTRL
GULF COAST...

...SYNOPSIS...
AN UPPER TROUGH LOCATED OVER THE SRN PLAINS IS FORECAST TO DEEPEN
AND AMPLIFY BY LATE AFTERNOON INTO TONIGHT OVER THE LOWER MS VALLEY.
AS THIS OCCURS...A MID/UPPER-LEVEL JET STREAK WILL ROUND THE BASE OF
THE TROUGH AND EMERGE OVER MS/AL. MEANWHILE...MORNING SURFACE
OBSERVATIONS SHOW AN AREA OF LOW PRESSURE OVER SERN TX...WITH A COLD
FRONT EXTENDING SWD INTO THE WRN GULF OF MEXICO...AND A STATIONARY
FRONT EXTENDING EWD ACROSS LA INTO SRN MS AND AL. THE LOW-LEVEL
CYCLONE IS FORECAST TO DEEPEN SLIGHTLY TONIGHT AS UPPER-LEVEL
DIVERGENCE INCREASES...WHICH WILL AID IN STRENGTHENING A SLY LLJ
OVER THE CNTRL GULF STATES. AS THE SURFACE LOW EXITS CNTRL LA AND
ENTERS CNTRL MS TONIGHT...THE COLD FRONT WILL ACCELERATE EWD OVER
SRN LA...AND REACH SRN MS/AL TOWARD THE END OF THE FORECAST PERIOD.

...LWR MS VALLEY/CNTRL GULF COAST...
A FRONTAL WAVE WILL MOVE ACROSS THE LWR MS VALLEY TODAY AS SURFACE
LOW PRESSURE ADVANCES FROM FAR SERN TX THIS MORNING INTO LA DURING
THE AFTERNOON...AND CNTRL MS BY TONIGHT. THE WARM SECTOR AIRMASS
WILL BE VERY MOIST...WITH SURFACE DEWPOINTS IN THE UPPER 60S TO LOW
70S...AND PW VALUES FROM 2.0-2.20 INCHES. HOWEVER...CLOUD COVER WILL
LIMIT SURFACE HEATING...AND MIDLEVEL LAPSE RATES WILL BE WEAK. AS A
RESULT...MUCAPE VALUES WILL RANGE FROM 500-1500 J/KG.

LINE SEGMENTS WILL BE LIKELY ALONG THE EWD ADVANCING COLD FRONT
DURING THE DAY...WHILE CLUSTERS OF STORMS WILL BE FORCED BY WEAK
WAA/ISENTROPIC UPGLIDE ALONG THE CNTRL GULF COAST AHEAD OF THE
FRONT. LOW-LEVEL SLY WINDS VEERING TO SWLY IN THE MIDLEVELS WILL
FAVOR A FEW ROTATING STORMS...AND PERHAPS A BRIEF TORNADO OR
DAMAGING WIND GUST. LATER TONIGHT...DEEP-LAYER WIND FIELDS ARE
FORECAST TO STRENGTHEN...WHICH COULD AID IN FURTHER STORM
ORGANIZATION AND SUBSEQUENT INCREASE IN TORNADO/DAMAGING WIND
POTENTIAL. HOWEVER...MODEL GUIDANCE INDICATES LARGE-SCALE FORCING
FOR ASCENT WILL BECOME DISPLACED TO THE N FROM THE MOIST/UNSTABLE
WARM SECTOR. THIS SHOULD PRECLUDE AN APPRECIABLE INCREASE IN THE SVR
WEATHER THREAT DURING THE NIGHT.

...CNTRL/SRN HIGH PLAINS...
A WEAK SURFACE TROUGH IS FORECAST TO EXTEND SWD FROM WRN NEB INTO
WRN TX THIS AFTERNOON. THE COMBINATION OF SURFACE DEWPOINTS FROM THE
UPPER 40S TO LOW 50S...TEMPERATURES IN THE 70S...AND STEEP MIDLEVEL
LAPSE RATES /FROM 7-7.5 C PER KM IN THE 700-500 MB LAYER/ WILL AID
IN WEAK MUCAPE VALUES RANGING FROM 500-1000 J/KG. THIS ENVIRONMENT
WILL YIELD ISOLATED THUNDERSTORMS DURING THE AFTERNOON ALONG THE
TROUGH. THOUGH DEEP-LAYER VERTICAL WIND SHEAR WILL GENERALLY BE WEAK
/20-30 KT OVER THE SRN HIGH PLAINS...15-20 KT OVER THE CNTRL HIGH
PLAINS/...ONE OR TWO STORMS MAY BRIEFLY PULSE UP TO SVR LEVELS AND
POSE A THREAT FOR A DAMAGING WIND GUST AND/OR LARGE HAIL.

..GARNER/THOMPSON.. 09/30/2012

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