DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 301559
SWODY1
SPC AC 301557

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1057 AM CDT SUN SEP 30 2012

VALID 301630Z - 011200Z

...THERE IS A SLGT RISK OF SVR TSTMS LOWER MS VALLEY/CNTRL GULF
COAST...

...SYNOPSIS...
THE SOUTHERN PLAINS UPPER TROUGH WILL AMPLIFY AND SHIFT EWD TOWARD
THE LOWER MS VALLEY TODAY. MID TO UPPER LEVEL FLOW IS FORECAST TO
STRENGTHEN AS A JET STREAK ROUNDS THE BASE OF THE TROUGH AND
OVERSPREADS THE CENTRAL GULF COAST STATES TONIGHT. AT THE SFC...THE
LOW NEAR THE SABINE RIVER VALLEY THIS MORNING IS EXPECTED TO DEEPEN
AND MIGRATE EWD ALONG THE CENTRAL GULF COAST TO NEAR SRN MS/AL BY
12Z MONDAY. A COLD FRONT EXTENDING SWD FROM THIS LOW AND A NWD
ADVANCING WARM FRONT ACROSS MS/AL WILL SERVE AS LOW LEVEL FOCUS FOR
THUNDERSTORM DEVELOPMENT TODAY AND TONIGHT...SOME OF THESE STORMS
WILL HAVE THE POTENTIAL TO PRODUCE STRONG WINDS AND PERHAPS A FEW
BRIEF TORNADOES. FURTHER WEST...A WEAK SFC TROUGH STRETCHING ACROSS
THE CNTRL AND SRN HIGH PLAINS WILL PROVIDE FOCUS FOR A FEW STORMS
THIS AFTERNOON AND EVENING.

...LOWER MS VALLEY/CNTRL GULF COAST...
WIDESPREAD CLOUDINESS WILL LIMIT HEATING/DESTABILIZATION ACROSS MUCH
OF THE REGION TODAY BUT SOME BREAKS IN CLOUDS IN SRN LA AND POSSIBLY
INTO FAR SRN MS WILL ALLOW FOR GREATER DESTABILIZATION FURTHER S.
RESULTING POOR LAPSE RATES WILL LIMIT MUCAPE VALUES TO AROUND
750-1500 J/KG DESPITE VERY MOIST AIRMASS. WHILE MARGINAL
THERMODYNAMIC ENVIRONMENT IS EXPECTED...DEEP LAYER SHEAR WILL
INCREASE THROUGH THE DAY AND INTO THE OVERNIGHT HOURS AS UPPER
TROUGH SHIFTS EWD AND AMPLIFIES. AT THE SAME TIME...SFC LOW WILL
STRENGTHEN WITH A RESPONDING INCREASE IN LOW LEVEL WINDS...WITH A
SLY LOW LEVEL JET AROUND 30-35 KT FORECAST TO DEVELOP ACROSS FAR SE
LA INTO SRN/CNTRL MS/AL TONIGHT. FURTHERMORE...VEERING VERTICAL WIND
PROFILES WITH INCREASING SPEED SHEAR WILL LEAD TO A THREAT FOR A FEW
TORNADOES AND STRONG/DAMAGING WINDS AS LINE SEGMENTS DEVELOP AHEAD
OF EWD ADVANCING COLD FRONT FROM SRN LA/MS THIS AFTERNOON INTO SRN
AL/FAR WRN FL PANHANDLE TONIGHT. FURTHER NORTH...ADDITIONAL
THUNDERSTORM DEVELOPMENT IS EXPECTED IN WAA REGIME ALONG AND NORTH
OF A W-E ORIENTED WARM FRONT FROM CNTRL/NRN MS/AL. IT SHOULD BE
NOTED THAT STRONGER FORCING FOR ASCENT WILL BE DISPLACED SLIGHTLY TO
THE NORTH...TN/NRN MS/AL...OF BEST SEVERE POTENTIAL...PERHAPS
LIMITING COVERAGE OF STRONGER/SEVERE STORMS GIVEN MARGINAL
THERMODYNAMIC ENVIRONMENT.

...CNTRL/SRN HIGH PLAINS...
A WEAK SFC TROUGH WILL DEVELOP ACROSS THE HIGH PLAINS
TODAY...PROVIDING FOCUS FOR ISOLATED THUNDERSTORM DEVELOPMENT THIS
AFTERNOON. A DRY BOUNDARY LAYER AND TEMPERATURES WARMING INTO THE
UPPER 70S/LOW 80 WILL RESULT IN STEEP LOW LEVEL LAPSE RATES AND LEAD
TO HIGH BASED STORMS. MLCAPE VALUES APPROACHING 500-1000 J/KG AND
STEEP MID LEVEL LAPSE RATES/COOL TEMPERATURES ALOFT SHOULD PROVIDE A
BRIEF WINDOW OF OPPORTUNITY FOR AN ISOLATED STRONG/SVR WIND GUST OR
POSSIBLY LARGE HAIL. ABSENCE OF STRONGER DEEP LAYER SHEAR AND
FOCUSED DEEP LAYER FORCING WILL LIMIT COVERAGE AND ORGANIZED SEVERE
THREAT.

..LEITMAN/HART.. 09/30/2012

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