SWODY2
SPC AC 171729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT SAT SEP 17 2011
VALID 181200Z - 191200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF CENTRAL
TX...CENTRAL OK TO SERN KS SUNDAY AFTERNOON AND EVENING...
...SYNOPSIS...
MODELS MAINTAIN A PROGRESSIVE/RELATIVELY LOW AMPLITUDE UPPER FLOW
REGIME PERSISTING THROUGH SUNDAY...WITH THE MAIN BELT OF WESTERLIES
CONFINED TO THE NORTHERN THIRD OF THE CONUS TO ADJACENT PART OF SRN
CANADA. THIS PATTERN WILL BE HIGHLIGHTED BY AN EASTWARD-MOVING
SHORTWAVE TROUGH UNDERGOING A DEGREE OF AMPLIFICATION OVER THE NRN
EXTENT OF THE NRN PLAINS/UPPER MIDWEST AND SASKATCHEWAN/MANITOBA/
NORTHERN ONTARIO. MEANWHILE...A TROUGH AXIS WITH EMBEDDED VORTICITY
MAXIMA /OVER NRN UT/SWRN WY AND NRN AZ TODAY/ WILL ADVANCE EWD
ACROSS THE CENTRAL AND SRN PLAINS DURING THE DAY 2 FORECAST PERIOD.
IN THE LOW LEVELS AT 12Z SUNDAY...A GENERALLY N-S ORIENTED SURFACE
FRONT WILL EXTEND FROM THE DAKOTAS INTO THE CENTRAL PLAINS AND THEN
TRAIL SWWD INTO W TX. THIS BOUNDARY WILL ADVANCE EWD ON SUNDAY
ATTENDANT TO THE EWD PROGRESSION OF THE MID-UPPER LEVEL TROUGH.
...PARTS OF CENTRAL TX...CENTRAL OK INTO SERN KS...
FORECAST CONFIDENCE IS A LITTLE GREATER FOR A FOCUSED CORRIDOR OF
STRONG TO SEVERE STORMS ON SUNDAY AFTERNOON/EVENING INVOF THE I-44
CORRIDOR IN OK INTO SERN KS...AND GENERALLY W OF THE I-35 CORRIDOR
IN CENTRAL TX. THUS...A RELATIVELY NARROW SLIGHT RISK AREA HAS BEEN
ADDED TO THE DAY 2 CONVECTIVE OUTLOOK.
LATEST TRENDS IN 12Z MODELS SUGGEST A DIFFERENTIAL HEATING
BOUNDARY/STRONGER SURFACE HEATING ARE EXPECTED ACROSS THE WRN EXTENT
OF THE DAY 2 SLIGHT RISK AREA INVOF THE SLOW EWD ADVANCING SURFACE
FRONT. THIS BOUNDARY SHOULD EXTEND FROM ERN KS SSWWD THROUGH
CENTRAL OK TO NW-WEST CENTRAL TX TO THE TX BIG BEND REGION BY MID
SUNDAY AFTERNOON. DESTABILIZATION WITHIN A MOIST AIR MASS /PW
VALUES AROUND 1.5 INCH/ IS EXPECTED TO RESULT IN MODERATE
INSTABILITY ALONG AND E OF THE FRONT. ALTHOUGH EFFECTIVE BULK SHEAR
IS NOT EXPECTED TO BE ANY STRONGER THAN INDICATED IN THE INITIAL DAY
2 OUTLOOK /20-30 KT/...THE DEGREE OF FORECAST INSTABILITY AND TIMING
OF FORCING FOR ASCENT WITH THE MID-UPPER LEVEL TROUGH SUGGEST STORMS
SHOULD FORM INVOF THE SURFACE FRONT. MULTICELLS WILL BE THE PRIMARY
STORM MODE WITH HAIL AND STRONG WIND GUSTS BEING THE MAIN SEVERE
WEATHER THREATS. THIS SCENARIO FOR CONVECTIVE DEVELOPMENT SUNDAY
AFTERNOON ALONG THE FRONT IS SUPPORTED BY MOST MODEL DATA...
INCLUDING A MAJORITY OF THE SREF MEMBERS. WHILE CONVECTION AND
EMBEDDED TSTMS WILL LIKELY PERSIST EWD THROUGH THE EVENING/SUNDAY
NIGHT TOWARD THE MID MS VALLEY TO ERN OK...WEAKENING INSTABILITY
SHOULD SUPPORT A DIMINISHING SEVERE WEATHER THREAT AFTER DARK.
..OZARKS TO LOWER MO/MID MS VALLEYS...
LOW LEVEL WAA IS EXPECTED TO SUPPORT CONVECTION/CLOUDINESS THROUGH
MUCH OF THE FORECAST PERIOD...WITH EMBEDDED AREAS OF STRONGER
STORMS. HOWEVER...OVERALL WEAKER DEEP LAYER SHEAR AND MARGINAL
INSTABILITY ARE EXPECTED TO PRECLUDE A GREATER SEVERE WEATHER THREAT
POTENTIAL WITH NEWD EXTENT.
..PETERS.. 09/17/2011
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