SWODY2
SPC AC 241729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT SUN MAY 24 2009
VALID 251200Z - 261200Z
...NO SVR TSTM AREAS FORECAST...
...NRN AND CNTRL PLAINS...
A SUBTLE UPPER-LEVEL TROUGH IS FORECAST TO MOVE EWD INTO THE NRN
PLAINS MONDAY AS A FAST-MOVING COLD FRONT ADVANCES SEWD ACROSS THE
DAKOTAS. AHEAD OF THE FRONT...A CLUSTER OF THUNDERSTORMS SHOULD BE
ONGOING IN NORTH DAKOTA MONDAY MORNING ON THE NOSE OF A WELL-FOCUSED
LOW-LEVEL JET. THIS ACTIVITY SHOULD BE ELEVATED MOVING EWD ACROSS
ERN ND DURING THE LATE MORNING. ADDITIONAL STORM DEVELOPMENT SHOULD
OCCUR BY EARLY AFTERNOON ALONG AND AHEAD OF A COLD FRONT AS
INSTABILITY INCREASES. THIS ACTIVITY SHOULD BE SFC-BASED AND MAY
CONGEAL INTO A LINE OF STRONG STORMS LATE MONDAY AFTERNOON AS SOME
MODEL FORECAST SUGGEST.
FORECAST SOUNDINGS ALONG THE BOUNDARY BY 00Z TUE SHOW THE GREATEST
VERTICAL SHEAR PROFILES ASSOCIATED WITH THE LOW-LEVEL JET OVER ERN
ND AND NW MN. IF ENOUGH INSTABILITY CAN DEVELOP IN THIS AREA...A
SUPERCELL WITH LARGE HAIL WOULD BE POSSIBLE. HOWEVER...THE STRONGER
INSTABILITY IS FORECAST FROM NRN NEB NNEWD ACROSS ERN SD WHERE
VERTICAL SHEAR WILL NOT BE AS STRONG LIMITING STORM ORGANIZATION. IN
SPITE OF THE WEAKER VERTICAL SHEAR...SFC DEWPOINTS IN THE LOWER 60S
F...STEEP LOW-LEVEL LAPSE RATES AND 20 KT OF FLOW ABOVE THE BOUNDARY
LAYER SHOULD BE ENOUGH FOR MARGINALLY SEVERE WIND GUSTS.
...SRN PLAINS...
AN AXIS OF INSTABILITY IS FORECAST ACROSS THE SRN PLAINS MONDAY FROM
THE TX HILL COUNTRY EXTENDING NNWWD INTO THE TX PANHANDLE. SCATTERED
THUNDERSTORMS SHOULD INITIATE MONDAY AFTERNOON AS A CAP WEAKENS AND
INSTABILITY INCREASES. FORECAST SOUNDINGS ALONG THE INSTABILITY AXIS
AT 00Z TUE SHOW 30 TO 40 KT OF VERTICAL SHEAR FROM THE LOW-ROLLING
PLAINS SWD INTO SOUTH TX MAINLY DUE TO DIRECTIONAL TURNING IN THE
LOW TO MID-LEVELS. THIS SHOULD BE SUFFICIENT FOR AN ISOLATED SEVERE
THREAT AS STORMS INCREASE IN COVERAGE DURING THE AFTERNOON. THE
SEVERE THREAT SHOULD BE DEPENDENT ON THE PRESENCE OF SUBTLE
PERTURBATIONS IN THE FLOW AND UPON WHERE THE STRONGEST INSTABILITY
DEVELOPS BY LATE AFTERNOON. SOME MODELS SUGGEST THE SHEAR AND
INSTABILITY COMBINATION WILL BE SUFFICIENT FOR SUPERCELLS IN SOUTH
TX. HOWEVER...THE MODELS DISAGREE CONCERNING THE CONVECTIVE
POTENTIAL IN THIS AREA SO WILL KEEP THE PROBABILITIES AT 5 PERCENT.
..BROYLES.. 05/24/2009
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