ACUS01 KWNS 251237
SWODY1
SPC AC 251235
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0735 AM CDT SUN SEP 25 2011
VALID 251300Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM CNTRL/ERN PARTS OF AR INTO
THE LOWER OH VALLEY...
...ARKLATEX INTO LOWER OH VALLEY...
MID- AND UPPER-LEVEL LOW OVER NWRN IL/ERN IA WILL DRIFT WWD TODAY
BEFORE TURNING MORE SEWD DURING THE LATTER HALF OF THE D1 PERIOD.
THIS IRREGULAR MOTION IS ATTRIBUTABLE TO A NUMBER OF VORTICITY
MAXIMA ROTATING AROUND PARENT CIRCULATION. IN THE LOW
LEVELS...SURFACE CYCLONE OVER S-CNTRL OK IS FORECAST TO DEVELOP EWD
ALONG ATTENDANT WARM FRONT TO THE VICINITY OF THE ARKLATEX BY LATE
AFTERNOON BEFORE ACCELERATING NNEWD THROUGH THE LOWER OH VALLEY TO
NEAR CHICAGO BY 26/12Z. MEANWHILE...TRAILING COLD FRONT WILL
ADVANCE SEWD THROUGH THE SRN PLAINS INTO LOWER MS VALLEY.
THE RETURN OF AN MT AIR MASS IS UNDERWAY ACROSS ERN TX/WRN LA...A
TREND WHICH SHOULD CONTINUE INTO AR TODAY...BUT IN A NARROWING
FASHION BETWEEN THE SURFACE FRONT AND A DEEPLY MIXED AND DRIER
BOUNDARY LAYER DEVELOPING OVER THE MS DELTA. THIS PROCESS WILL
OCCUR BENEATH ERN EXTENSION OF EML PLUME EMANATING FROM THE SRN
ROCKIES...YIELDING A MODERATELY UNSTABLE AIR MASS BY AFTERNOON FROM
CNTRL AR INTO NERN TX WHERE MLCAPE WILL APPROACH 1500-2000 J/KG.
ELEVATED TSTMS ONGOING OVER SRN MO INTO THE LOWER OH VALLEY AND SWD
INTO CNTRL AR MAY PERSIST TODAY...DRIVEN BY LOW-LEVEL WAA AND DCVA
IN ADVANCE OF VORTICITY MAXIMUM ROTATING SEWD THROUGH THE OZARK
PLATEAU. STORMS MAY BECOME PROGRESSIVELY MORE SURFACE BASED BY
AFTERNOON ACROSS AR AS THE BOUNDARY LAYER CONTINUES TO
MOISTEN/DESTABILIZE. ADDITIONAL...MORE ISOLATED STORM DEVELOPMENT
WILL BE POSSIBLE SWWD TOWARD THE ARKLATEX AS CAP IS ERODED BY STRONG
DIABATIC HEATING FORECAST W OF DRYLINE AND AHEAD OF COLD FRONT.
THE CORRIDOR FROM THE SURFACE LOW NEWD ALONG SURFACE FRONT /I.E.
SW-CNTRL-NE AR/ APPEARS MOST FAVORABLE FOR SEVERE STORM DEVELOPMENT
THIS AFTERNOON AND EVENING. HERE...A MOIST AND MODERATELY UNSTABLE
BOUNDARY LAYER WILL ALIGN WITH A KINEMATIC ENVIRONMENT FEATURING
EFFECTIVE SRH OF 150-250 M2/S2 AND 40-50 KT OF DEEP-LAYER SHEAR.
THIS SETUP WILL BE SUPPORTIVE OF ORGANIZED STORM MODES INCLUDING
SUPERCELLS WITH A RISK FOR A COUPLE TORNADOES...LARGE HAIL AND
DAMAGING WINDS. STORMS ARE EXPECTED TO DEVELOP NEWD THROUGH WRN
PARTS OF TN/KY THIS EVENING WITHIN A ZONE OF ENHANCED ISALLOBARIC
FORCING ALONG SURFACE LOW TRACK. WHILE INSTABILITY WILL DIMINISH
WITH NWD EXTENT...VERTICAL SHEAR WILL PROGRESSIVELY STRENGTHEN WITH
A CONTINUED RISK FOR DAMAGING WINDS AND PERHAPS A TORNADO OR TWO.
...OH VALLEY TONIGHT...
MOIST AIR MASS CURRENTLY IN PLACE E OF THE APPALACHIANS WILL BE
DRAWN WWD AS LOW-LEVEL FLOW FIELD STRENGTHENS IN RESPONSE TO
APPROACH OF SURFACE LOW. WHILE LAPSE RATES WILL REMAIN WEAK...THE
MOISTENING ENVIRONMENT IS FORECAST TO YIELD POCKETS OF WEAK ELEVATED
INSTABILITY WHICH WILL BE SUFFICIENT TO SUPPORT AN INCREASE IN TSTMS
TONIGHT FROM KY NWD INTO IND/OH. LOCALLY STRONG WIND GUSTS MAY
ACCOMPANY THE MOST INTENSE STORMS GIVEN SSWLY WINDS INCREASING TO
50+ KT JUST ABOVE THE GROUND.
..MEAD/ROGERS.. 09/25/2011
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