SWODY1
SPC AC 181635
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1135 AM CDT TUE SEP 18 2007
VALID 181630Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR
CENTRAL KS TO SE NEB...
..IA/MN/WI TODAY INTO TONIGHT...
THE MID LEVEL TROUGH OVER ERN CO WILL EJECT NEWD TOWARD IA/MN BY
TONIGHT AS A LARGER UPSTREAM WAVE AMPLIFIES OVER THE PAC NW
COAST...WHILE AN ASSOCIATED SURFACE CYCLONE MOVES EWD TO THE
IMMEDIATE N OF THE MN/ONTARIO BORDER. TRAILING THIS CYCLONE...A
COLD FRONT WILL MOVE SEWD ACROSS NEB/IA/MN/WI BY EARLY WEDNESDAY.
THE ERN CO SHORTWAVE TROUGH IS PRECEDED BY SEVERAL SMALLER SCALE
VORTICITY MAXIMA IN A BELT FROM SW OK TO SE MN AND NW WI.
THESE LEAD SYSTEMS ARE ASSOCIATED WITH WIDESPREAD PRE-FRONTAL CLOUDS
AND RAINFALL ALONG THE LOW-LEVEL MOISTURE AXIS...WHICH WILL TEND TO
LIMIT MID LEVEL LAPSE RATES AND SURFACE HEATING FROM WRN/NRN IA
ACROSS MN/WRN WI TODAY. THERE WILL BE SOME THREAT FOR EMBEDDED
STORMS WITH DAMAGING WINDS GIVEN THE 40-50 KT FLOW IN THE 800-500 MB
LAYER...AND PERHAPS A TORNADO...BUT THE WEAK INSTABILITY WILL LIMIT
THE OVERALL SEVERE STORM THREAT FROM IA TO WI. STRONGER SURFACE
HEATING IS EXPECTED ALONG THE SERN FRINGE OF THE CLOUD BAND...FROM
NW MO ACROSS SRN/ERN IA INTO SW WI. THIS CORRIDOR WILL BE JUST E OF
THE RICHER BOUNDARY LAYER MOISTURE...THOUGH STEEPER LOW-LEVEL LAPSE
RATES WITH THE BELT OF STRONG LOW-MID LEVEL FLOW MAY PROMOTE A FEW
STRONG/ISOLATED DAMAGING GUSTS DURING THE AFTERNOON.
..CENTRAL KS/S CENTRAL NEB THIS AFTERNOON...
THE PRIMARY MID LEVEL WAVE OVER ERN CO WILL TRAVERSE WRN/CENTRAL KS
AND NEB BY LATE AFTERNOON...WHILE THE SURFACE COLD FRONT DRIFTS SEWD
ACROSS CENTRAL NEB AND THE LEE TROUGH/DRYLINE MOVES SLOWLY EWD
ACROSS WRN KS. W OF THE INITIAL CLOUD/RAIN BAND...EXPECT STRONGER
SURFACE HEATING AND STEEPER LOW-MID LEVEL LAPSE RATES COMPARED TO
AREAS FARTHER NE. BOUNDARY LAYER DEWPOINTS IN THE MID 60S AND
SURFACE TEMPERATURES IN THE LOW-MID 80S WILL SUPPORT MLCAPE VALUES
OF 1500-2000 J/KG IN A NARROW CORRIDOR BETWEEN THE CLOUD BAND AND
THE DRYLINE.
SCATTERED THUNDERSTORMS WILL LIKELY DEVELOP BY EARLY-MID AFTERNOON
FROM THE DRYLINE/COLD FRONT INTERSECTION SWD ALONG THE
DRYLINE...ROUGHLY ALONG AND E OF A DDC TO EAR LINE AROUND 20-21Z.
THOUGH LOW-LEVEL FLOW/SHEAR WILL WEAKEN IN THE WARM SECTOR AS THE
PRIMARY LLJ SHIFTS WELL NE OF KS...DEEP LAYER VERTICAL SHEAR SHOULD
STILL BE SUFFICIENT FOR A FEW SUPERCELLS WITH LARGE HAIL AND
DAMAGING WINDS. CONVECTION SHOULD PERSIST INTO THE OVERNIGHT HOURS
WHILE SPREADING NEWD FROM KS INTO IA...THOUGH WEAKENING INSTABILITY
AND VERTICAL SHEAR BOTH SUGGEST THAT THE SEVERE THREAT WILL DIMINISH
BY 03Z.
.THOMPSON/JEWELL.. 09/18/2007
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