DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 230555
SWODY1
SPC AC 230554

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT TUE SEP 23 2008

VALID 231200Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MS
VALLEY AND MID-MO VALLEY...

...UPPER MS VALLEY/MID-MO VALLEY...
A WELL-DEFINED UPPER-LEVEL TROUGH OVER THE NRN ROCKIES WILL MOVE
INTO THE NRN PLAINS TODAY. AHEAD OF THE UPPER-LEVEL TROUGH...A
LOW-LEVEL JET IS FORECAST ACROSS THE WARM SECTOR THIS MORNING.
NUMEROUS THUNDERSTORMS SHOULD BE ONGOING AT THE BEGINNING OF THE
PERIOD ALONG THE AXIS OF THE LOW-LEVEL JET FROM ECNTRL NEB NNEWD
ACROSS ERN SD INTO WRN MN. THIS ACTIVITY IS FORECAST TO SPREAD ENEWD
ACROSS THE UPPER MS VALLEY AND MAY DECREASE IN COVERAGE TOWARD
MIDDAY. BY MID-AFTERNOON...NUMEROUS THUNDERSTORMS APPEAR LIKELY TO
DEVELOP FROM MN SSWWD ACROSS WRN IA INTO SERN NEB AS A CAPPING
INVERSION DIMINISHES AND INSTABILITY INCREASES. MODEL FORECASTS
SUGGEST A SQUALL-LINE SHOULD DEVELOP ALONG THE INSTABILITY AXIS BY
EARLY EVENING. THIS LINE OF STORMS SHOULD GRADUALLY BECOME ELEVATED
MOVING EWD ACROSS NRN MN...WI AND ERN IA DURING THE OVERNIGHT
PERIOD.

CONCERNING THE SHEAR ENVIRONMENT...A WELL-DEFINED 60 TO 70 KT
MID-LEVEL JET IS FORECAST TO MOVE ACROSS SD THIS AFTERNOON WITHIN A
BAND OF STRONGER FLOW EXTENDING NEWD INTO WRN ONTARIO. AS THE
FEATURE MOVES INTO THE REGION FROM THE WEST...FORECAST SOUNDINGS IN
WRN MN INCREASE 0-6 KM SHEAR VALUES FROM ABOUT 35 KT AT 21Z TO ABOUT
50 KT BY 00Z. THIS SHOULD SUPPORT SUPERCELLS OR ORGANIZED SEVERE
MULTICELL LINE-SEGMENTS. THE GREATEST THREAT FOR WIND DAMAGE SHOULD
EXIST FROM ECNTRL MN SWWD INTO NW IA WHERE INSTABILITY SHOULD BE
MAXIMIZED AND UNIDIRECTIONAL WIND PROFILES ARE FORECAST. THE THREAT
FOR LARGE HAIL MAY BE GREATEST NEARER TO THE UPPER-LEVEL TROUGH
ACROSS THE FAR ERN DAKOTAS AND WRN MN WHERE STORMS SHOULD REMAIN
MORE DISCRETE AND MID-LEVEL LAPSE RATES ARE FORECAST TO BE QUITE
STEEP.

...SRN AND CNTRL PLAINS...
AN UPPER-LEVEL TROUGH WILL MOVE EWD ACROSS THE NRN PLAINS TODAY AS
WLY FLOW REMAINS IN PLACE ACROSS THE SRN AND CNTRL PLAINS. AT THE
SFC...A COLD FRONT WILL ADVANCE SLOWLY SSEWD ACROSS WCNTRL KS
REACHING THE OK PANHANDLE DURING THE LATE AFTERNOON. MODEL FORECASTS
INITIATE THUNDERSTORMS ALONG AN AXIS OF MODERATE INSTABILITY JUST
AHEAD OF THE COLD FRONT DURING THE AFTERNOON. ALTHOUGH LARGE-SCALE
ASCENT IS FORECAST TO BE WEAK...A DIMINISHING CAPPING INVERSION AND
STRONG LOW-LEVEL CONVERGENCE SHOULD BE SUFFICIENT FOR THE
DEVELOPMENT OF A CONVECTIVE LINE BY LATE AFTERNOON. FORECAST
SOUNDINGS JUST AHEAD OF THE FRONT IN WCNTRL KS SHOW SUBSTANTIAL
DIRECTIONAL SHEAR WITH ABOUT 30 KT AT 500 MB. THIS ALONG WITH STEEP
MID-LEVEL LAPSE RATES MAY BE ENOUGH FOR MARGINALLY SEVERE HAIL. THE
STORMS MAY ALSO BE ACCOMPANIED WITH STRONG WIND GUSTS DURING THE
LATE AFTERNOON WHEN LOW-LEVEL LAPSE RATES WILL BE QUITE STEEP.

..BROYLES/SMITH.. 09/23/2008

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