SPC AC 261957
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0157 PM CST THU FEB 26 2009
VALID 262000Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER TO MID MS VALLEY
REGION...
...LOWER TO MID MS VALLEY REGION...
THIS AFTERNOON A COLD FRONT EXTENDS FROM A SURFACE LOW IN NW MO SWWD
THROUGH NW OK INTO THE TX PANHANDLE. PRE-FRONTAL TROUGH OR DRYLINE
EXTENDS FROM SE KS SWWD THROUGH CNTRL OK AND N CNTRL TX. WARM FRONT
EXTENDS EWD FROM THE LOW THROUGH NRN MO...SRN IL AND SRN IND. AN
UPPER TROUGH WITH A COUPLE EMBEDDED VORTICITY MAXIMA WILL CONTINUE
EAST THROUGH THE MID-UPPER MS VALLEY TONIGHT. SURFACE LOW IS
FORECAST TO DEEPEN AS IT LIFTS NE INTO THE GREAT LAKES...WHILE
TRAILING COLD FRONT OVERTAKES THE DRYLINE AS IT ADVANCES EAST INTO
THE MID MS VALLEY THIS EVENING.
AXIS OF MODIFIED CP AIR HAS ADVECTED NEWD THROUGH PRE-FRONTAL WARM
SECTOR ACROSS ERN PARTS OF SRN PLAINS AND LOWER-MID MS VALLEY WITH
DEWPOINTS IN THE MID-UPPER 50S. THE ATMOSPHERE IS DESTABILIZING IN
NARROW CORRIDOR FROM NE TX...ERN OK...ERN KS AND WRN MO WHERE LOW
CLOUDS HAVE MIXED OUT WITH MLCAPE FROM 500 TO 1000 J/KG. STEEPER
MID-LEVEL LAPSE RATES ASSOCIATED WITH EML HAVE BEEN ADVECTING EWD
ABOVE THE MOIST AXIS. HOWEVER...THIS HAS RESULTED IN A SUBSTANTIAL
CAP ALONG INSTABILITY AXIS OVER WRN PORTIONS OF WARM SECTOR.
THE LOW LEVEL JET WILL STRENGTHEN AS IT DEVELOPS NE TOWARD THE OH
VALLEY EAST OF DEEPENING SURFACE LOW. STORMS WILL LIKELY CONTINUE
DEVELOPING WITHIN WARM ADVECTION REGIME OVER THE MID-MS AND GREAT
LAKES REGION INTO THE EVENING. AN 18Z SPECIAL RAOB FROM LINCOLN IL
SHOWS 7 C/KM MID-LEVEL LAPSE RATES AND 1200 J/KG MUCAPE ABOVE A
STABLE BOUNDARY LAYER. THIS ENVIRONMENT IS SUPPORTING A THREAT OF
HAIL WITH STORMS DEVELOPING WITHIN WARM ADVECTION REGIME.
HOWEVER...OVERALL HAIL THREAT WITH THIS ACTIVITY SHOULD BEGIN TO
DECREASE THIS EVENING AS THE STORMS MOVE INTO THE GREAT LAKES WHERE
INSTABILITY IS MORE MARGINAL.
AS THE COLD FRONT OVERTAKES THE REMNANT DRYLINE THIS EVENING INTO
EARLY TONIGHT ACROSS MO/ERN OK AND THE CAP WEAKENS FROM THE W...A
BAND OF THUNDERSTORMS IS EXPECTED TO DEVELOP ALONG THE FRONT. THIS
CONVECTION SHOULD BACK-BUILD WSWWD TO THE SE OK/EXTREME NE TX AREA
AND PERSIST THROUGH 12Z AS THE SURFACE FRONT STALLS NEAR THE RED
RIVER. THOUGH THE STRONGER LLJ CORE WILL DEVELOP NEWD INTO THE OH
VALLEY OVERNIGHT...DEEP LAYER VERTICAL SHEAR AND INSTABILITY WILL
REMAIN LARGE ENOUGH TO SUPPORT A THREAT FOR DAMAGING WINDS AND LARGE
HAIL WITH THE COLD FRONTAL STORMS THROUGH EARLY FRIDAY. A TORNADO
OR TWO MAY ALSO OCCUR WITH ANY EMBEDDED SUPERCELLS...MAINLY EARLY
TONIGHT BEFORE THE LOW-LEVEL FLOW WEAKENS.
..DIAL.. 02/26/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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