DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 310536
SWODY1
SPC AC 310534

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1234 AM CDT WED AUG 31 2011

VALID 311200Z - 011200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN
PLAINS...

...NRN PLAINS/NRN ROCKIES...
AN UPPER-LEVEL RIDGE OVER THE NRN HIGH PLAINS WILL MOVE EWD ACROSS
THE DAKOTAS TODAY AS AN UPPER-LEVEL TROUGH MOVES ACROSS PACIFIC
NORTHWEST. AN AXIS OF MODERATE TO STRONG INSTABILITY SHOULD BE IN
PLACE BENEATH THE RIDGE BY THIS AFTERNOON FROM THE MID-MO VALLEY
NWWD INTO THE DAKOTAS AND ERN MT. HOWEVER...WARM AIR ALOFT AND A
STRONG CAPPING INVERSION WILL KEEP CONVECTION FROM INITIATING IN THE
PLAINS THIS AFTERNOON. FURTHER TO THE WEST INTO THE NRN
ROCKIES...LARGE-SCALE ASCENT ASSOCIATED WITH THE UPPER-LEVEL TROUGH
WILL HELP SCATTERED THUNDERSTORMS TO INITIATE IN THE HIGHER TERRAIN
BY LATE AFTERNOON WITH CONVECTION MOVING ENEWD INTO THE NRN HIGH
PLAINS BY EARLY THIS EVENING. THE MAIN UNCERTAINTY CONCERNING THE
SLIGHT RISK AREA IS CONVECTIVE COVERAGE. MODEL CONSENSUS SUGGESTS
THAT CONVECTIVE COVERAGE WILL BE THE GREATEST IN ERN MT AND WRN ND.

FORECAST SOUNDINGS ACROSS ERN MT AND WRN ND AT 03Z THURSDAY SHOW AN
IMPRESSIVE ENVIRONMENT WITH MLCAPE VALUES OF 2000 TO 3000 J/KG...0-6
KM SHEAR VALUES AROUND 50 KT AND MID-LEVEL LAPSE RATES OF 8.0 TO 9.0
C/KM. AS STORMS INITIATE...THE ENVIRONMENT SHOULD SUPPORT SUPERCELL
DEVELOPMENT WITH A THREAT FOR HAIL AND ISOLATED WIND DAMAGE. THE
HAIL THREAT COULD BECOME ENHANCED IF SUPERCELLS CAN DEVELOP DURING
THE EARLY EVENING WHEN INSTABILITY WILL BE STRONGER.
HOWEVER...SEVERAL MODEL FORECASTS SUGGEST THE MORE INTENSE
CONVECTIVE DEVELOPMENT WILL HOLD OFF UNTIL THE LATE EVENING AS THE
LOW-LEVEL JET STRENGTHENS. THIS WOULD CONCENTRATE THE SEVERE THREAT
DURING THE OVERNIGHT PERIOD EWD INTO THE NRN PLAINS.

FURTHER SOUTH ACROSS WRN AND CNTRL SD...MODEL FORECASTS DISAGREE ON
WHETHER STORMS CAN INITIATE IN SPITE OF THE WARM AIR ALOFT. THE NAM
INITIATES ISOLATED THUNDERSTORMS AS FAR SOUTH AS PIERRE SD. IF THIS
OCCURS...THEN THE THREAT FOR LARGE HAIL COULD EXTEND INTO CNTRL SD.
CONSIDERED UPGRADING TO SLIGHT RISK ACROSS PARTS OF NCNTRL SD.
HOWEVER...DUE TO THE CAPPING INVERSION AND UNCERTAINTY CONCERNING
CONVECTIVE INITIATION...WILL MAINTAIN A 5 PERCENT WIND AND HAIL
PROBABILITY.

..BROYLES/GARNER.. 08/31/2011

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