ACUS01 KWNS 261253
SWODY1
SPC AC 261250
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT FRI SEP 26 2008
VALID 261300Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER THE UPR MS VLY...
...SYNOPSIS...
THE MAIN BELT OF THE WLYS WILL REMAIN CONFINED TO SRN PORTIONS OF
WRN/CNTRL CANADA THROUGH SATURDAY AS UPR LOW NOW OVER ERN SC MOVES
NW INTO WRN NC. ALONG THE SRN FRINGE OF THE WLYS...IMPULSE NOW OVER
CNTRL MT SHOULD CONTINUE E INTO WRN ND BY EVE...AND INTO MN EARLY
SATURDAY AS WEAKER LEAD DISTURBANCE OVER THE WRN DAKS SHEARS ENE
INTO MN/WRN ONTARIO.
AT LWR LVLS...COLD FRONT AND LEE TROUGH ASSOCIATED WITH MT/DAKS
SYSTEM SHOULD PROGRESS STEADILY ESE ACROSS THE UPR MS VLY/UPR GRT
LKS...WHILE WEAK SSW/NNE-ORIENTED BOUNDARY EDGES SLOWLY NW ACROSS
ERN/CNTRL NC AND SE VA.
...UPR MS VLY THIS AFTN INTO TNGT...
CLOUDS ASSOCIATED WITH LEAD UPR IMPULSE WILL SOMEWHAT LIMIT SFC
HEATING AHEAD OF COLD FRONT CROSSING MN LATER TODAY. NEVERTHELESS
...EVEN MODEST HEATING OF MODIFIED CP AIR BENEATH EXISTING EML PLUME
SHOULD SUPPORT 1000-1500 J/KG SBCAPE OVER NRN/CNTRL MN BY AFTN.
STORMS MAY INITIALLY DEVELOP IN POST FRONTAL ENVIRONMENT ACROSS NRN
MN LATER THIS MORNING THROUGH MID AFTN AS ASCENT STRENGTHENS
DOWNSTREAM FROM APPROACHING UPR IMPULSE. STRONGER...SFC-BASED
STORMS MAY FORM LATER THIS AFTN AND EVE ALONG THE FRONT AS EML CAP
IS BREACHED AND DESTABILIZATION/ASCENT CONTINUE.
40 KT LARGELY UNIDIRECTIONAL DEEP WSWLY SHEAR WILL SUPPORT
ORGANIZED/SUSTAINED STORMS...AND POSSIBLY A FEW ROTATING STRUCTURES.
BUT WIND PROFILES SUGGEST THAT PREDOMINANT CONVECTIVE MODE SHOULD
BE BROKEN LINE SEGMENTS. THE STORMS COULD YIELD ISOLD DMGG WIND AND
SVR HAIL THROUGH MID EVENING.
LARGE SCALE ASCENT SHOULD INCREASE OVER THE UPR MS VLY LATE
TONIGHT/EARLY SATURDAY AS HIGH LVL JET ENTRANCE REGION DEVELOPS N OF
LK SUPERIOR AND MAIN UPR TROUGH APPROACHES FROM THE WEST. THIS
SETUP COULD SUPPORT ADDITIONAL STORM DEVELOPMENT...WITH POSSIBLE
BACK-BUILDING ACTIVITY...ALONG THE STILL-PROGRESSIVE COLD FRONT FROM
NRN/WRN WI SW INTO SRN MN AND POSSIBLY NRN IA.
...ERN NC TO LWR CHESAPEAKE BAY THIS AFTN/EVE...
SATELLITE AND PRESSURE CHANGE DATA SUGGEST THAT HYBRID... VERTICALLY
STACKED SC LOW WILL CONTINUE SLOWLY WNW TODAY. IT SHOULD WEAKEN AS
IT MOVES FARTHER AWAY FROM THE CST. HOWEVER... PLUME OF TROPICAL
AIR /WITH SFC DEWPOINTS AROUND 70/ WILL CONTINUE TO SPREAD ACROSS
NRN/ERN NC AND SE VA ON ERN SIDE OF SYSTEM... BENEATH MID LVL DRY
SLOT.
ALTHOUGH THE STRONGEST/MOST SUSTAINED CONVECTION SHOULD REMAIN
OFFSHORE...DIURNAL DESTABILIZATION IN DRY SLOT MAY SUPPORT
REDEVELOPMENT OF BANDS/CLUSTERS OF SHOWERS AND STORMS IN AN ARC FROM
THE OUTER BANKS OF NC NW INTO S CNTRL/SE VA. COUPLED WITH RICH
MOISTURE AND RESIDUAL BAND OF MODERATE FLOW...SETUP COULD YIELD ONE
OR TWO ISOLD TORNADOES. THIS THREAT WOULD BE GREATEST AS
SHOWERS/STORMS CROSS AXIS OF ENLARGED LOW-LVL HODOGRAPHS ALONG
AFOREMENTIONED SSW/NNE SFC BOUNDARY THIS AFTN.
..CORFIDI/GRAMS.. 09/26/2008
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