SWODY1
SPC AC 071621
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1121 AM CDT TUE OCT 07 2008
VALID 071630Z - 081200Z
...NO SVR TSTM AREAS FORECAST...
...LOWER MS VALLEY TODAY INTO TONIGHT...
A PAIR OF LOOSELY PHASED SHORTWAVE TROUGHS WILL MOVE EWD OVER THE MS
VALLEY THROUGH TONIGHT...WITH THE MAJORITY OF THE DEEP CONVECTION
LINKED TO THE SRN TROUGH ACROSS THE LOWER MS VALLEY. A LEAD TROUGH
IS EJECTING NEWD OVER NE TX/AR WITHIN THE BROADER SRN TROUGH...WHILE
THE PRIMARY UPSTREAM WAVE NOW OVER OK WILL PROGRESS ESEWD TO THE
ARKLAMISS REGION LATE TONIGHT. AT THE SURFACE...A WEAK CYCLONE IN
WRN MO IS EXPECTED TO DEVELOP EWD ACROSS MO/IL THROUGH EARLY TONIGHT
WHILE A TRAILING COLD FRONT MOVES EWD FROM ERN OK/TX ACROSS AR/LA.
THE COLD FRONT IS PRECEDED BY A PRE-FRONTAL TROUGH AND A BAND OF
THUNDERSTORMS ALONG AN AXIS FROM ROUGHLY MLU TO LCH. FARTHER E...A
RESIDUAL BAROCLINIC ZONE MARKS THE NE EDGE OF THE RICHER MOISTURE
FROM WRN TN SSEWD ACROSS NE MS INTO SW AL.
THE PRE-FRONTAL CONVECTIVE BAND ACROSS LA SHOULD PERSIST INTO THE
AFTERNOON AS THE BOUNDARY LAYER WARMS AND CONVECTIVE INHIBITION IS
ELIMINATED ACROSS THE LA/MS WARM SECTOR. MODIFIED 12Z
SOUNDINGS...DESPITE MODEST MID LEVEL LAPSE RATES OF 6-6.5 C/KM...
SUGGEST THAT AFTERNOON MLCAPE VALUES WILL LIKELY REACH 1000-1500
J/KG TOWARD NRN MS/AR WITH SURFACE TEMPERATURES OF 75-80 F AND
DEWPOINTS OF 68-70 F...AND 2000 J/KG FARTHER S INTO SRN LA WITH
SURFACE TEMPERATURES IN THE MID 80S WITH MID 70S DEWPOINTS.
HOWEVER...SOUNDINGS AND RECENT VWP/S SHOW WEAK VERTICAL SHEAR
/ESPECIALLY IN THE LOW LEVELS/ S OF I-20 WHERE INSTABILITY WILL BE
GREATEST...AND A LITTLE STRONGER LOW-LEVEL SHEAR ACROSS NRN MS/WRN
TN ALONG THE RESIDUAL BAROCLINIC ZONE WHERE INSTABILITY WILL BE
WEAKER. THE COMBINATION OF INGREDIENTS APPEARS RATHER MARGINAL FOR
AN ORGANIZED SEVERE STORM THREAT IN EITHER AREA THIS
AFTERNOON...ASIDE FROM MARGINALLY SEVERE HAIL AND ISOLATED DAMAGING
OUTFLOW GUSTS. A BRIEF/WEAK TORNADO CANNOT BE RULED OUT THIS
AFTERNOON AS DIURNAL INSTABILITY IS MAXIMIZED...AND INTO TONIGHT AS
LOW-LEVEL FLOW INCREASES SOME OVER AL WITH THE APPROACH OF THE MID
LEVEL TROUGH FROM THE W. STILL...THE TORNADO THREAT SHOULD REMAIN
MARGINAL THROUGH THE PERIOD.
...MT AREA THIS AFTERNOON/EVENING...
A STRONG NRN STREAM SHORTWAVE TROUGH AND AN ASSOCIATED COLD FRONT
WILL MOVE QUICKLY EWD OVER CENTRAL/ERN MT THIS AFTERNOON/EVENING.
LOW-LEVEL MOISTURE/INSTABILITY WILL BE QUITE LIMITED ACROSS MT
TODAY...THOUGH MID LEVEL MOISTENING AND STEEPENING LOW-LEVEL LAPSE
RATES MAY BE SUFFICIENT FOR SOME LOW-TOPPED CONVECTION WITH GUSTY
WINDS ALONG THE FRONT.
..THOMPSON/JEWELL.. 10/07/2008
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