SWODY1
SPC AC 211259
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0659 AM CST WED NOV 21 2007
VALID 211300Z - 221200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM E TX AND THE ARKLATEX INTO
THE LWR MS AND TN VLYS...
..SYNOPSIS...
CHANGE TO AN INCREASINGLY AMPLIFIED AND CYCLONIC PATTERN OVER THE
CONUS WILL CONTINUE THIS PERIOD. SHORTWAVE TROUGH NOW OVER THE
CNTRL RCKYS CONTINUES E TO THE LWR MO VLY THIS EVENING AND ENE TO
NEAR LK HURON EARLY THURSDAY AS UPSTREAM DISTURBANCE NOW ENTERING MT
AMPLIFIES SSE TOWARD THE CNTRL HI PLNS. 70-80 KT MID-LVL JET
STREAK ROUNDING BASE OF RCKYS TROUGH WILL MOVE E/NE INTO MO/IL
THIS EVENING...WHILE SRN STREAM DISTURBANCES CONTINUE TO ACCELERATE
NEWD ON PERIPHERY OF THIS JET ACROSS THE LWR MS VLY.
AT THE SFC...WAVE NOW OVER SW MO SHOULD SLOWLY DEEPEN AS IT
CONTINUES NE INTO IND THIS EVENING...AND TO NEAR PIT EARLY THURSDAY.
TRAILING...STRONG COLD FRONT WILL MOVE E/SE ACROSS AR AND E TX
TODAY...AND THE LWR OH/MS AND TN VLYS TONIGHT AND EARLY THURSDAY.
THIS BOUNDARY SHOULD BE THE MAIN FOCUS FOR STRONG TO POTENTIALLY
SEVERE TSTM DEVELOPMENT THIS AFTN INTO TONIGHT.
..ARKLATEX INTO LWR MS/TN VLY VLYS...
SFC...SATELLITE AND RAOB DATA SHOW FAIRLY RICH LOW TO MID LVL
MOISTURE...WITH SFC DEWPOINTS RANGING FROM THE UPR 50S TO MID 60S
AND MIXING RATIOS UP TO 13 G/KG...CONTINUING TO STREAM NEWD AHEAD OF
AFOREMENTIONED COLD FRONT FROM ERN PARTS OF THE SRN PLNS INTO THE
LWR/MID MS VLY. WHILE MID LVL LAPSE RATES LIKELY WILL REMAIN WEAK
/AROUND 6.5-7.0 C PER KM/...COMBINATION OF MODEST HEATING AND
CONTINUED MOISTURE INFLOW SHOULD SUPPORT AFTN MLCAPE OF 500-1000
J/KG OVER NRN PORTIONS OF SLIGHT RISK AREA...WITH VALUES AOA
1500-2000 J/KG IN SE TX/LA.
PRE-FRONTAL STORMS NOW OVER AR LIKELY ARE FORMING IN ZONE OF
ENHANCED WAA ASSOCIATED WITH 30-35 KT SWLY LLJ AND ASCENT ASSOCIATED
WITH SRN STREAM IMPULSES. THIS ACTIVITY MAY INCREASE IN COVERAGE
THROUGH THE DAY...EWD INTO TN/AL AND SWD INTO MS...ALONG ERN EDGE OF
AXIS OF LOW LVL MOISTURE RETURN. OTHER STORMS MAY DEVELOP N FROM
THE N CNTRL GULF OF MEXICO ALONG SAME THETA-E GRADIENT INTO SE MS.
A FEW OF THESE STORMS MAY DEVELOP ORGANIZED/ROTATING UPDRAFTS AND
POSE A THREAT FOR LOCALLY DAMAGING WIND AND PERHAPS A TORNADO.
MORE WIDESPREAD/POTENTIALLY VIGOROUS DEVELOPMENT IS EXPECTED THIS
AFTN ALONG COLD FRONT FROM SE MO/NE AR SWWD INTO THE ARKLATEX AND
EVENTUALLY SE TX AS STRONGER HEIGHT FALLS ASSOCIATED WITH PASSING
TROUGH OVERSPREAD DESTABILIZING AIR MASS. WHILE THE STRONGER
MID AND HIGH-LEVEL WINDS WILL LAG SFC WARM SECTOR TO THE W/NW...
35-40 KT OF DEEP SWLY SHEAR SHOULD EXIST OVER THE LWR TN VLY...
DECREASING TO 25-30 KT ACROSS THE ARKLATEX.
COMBINATION OF MODERATE INSTABILITY/DEEP SHEAR AND LINEAR LOW LVL
FORCING OF FRONT SUGGESTS ORGANIZATION OF STORMS INTO LINE
SEGMENTS...WITH EMBEDDED BOWING AND SUPERCELL STRUCTURES POSING A
THREAT FOR DAMAGING WIND...HAIL AND PERHAPS A TORNADO OR TWO.
THIS THREAT LIKELY WILL CONTINUE ACROSS WRN TN AND NRN/CNTRL
PARTS OF MS BEFORE WEAKENING LATER TONIGHT AS BOUNDARY LAYER SLOWLY
COOLS.
.CORFIDI/GUYER.. 11/21/2007
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