DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 200713
SWODY3
SPC AC 200712

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0212 AM CDT THU MAY 20 2010

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE ERN DAKOTAS
AND WRN MN...

...NRN PLAINS...
AN UPPER-LEVEL TROUGH IS FORECAST TO REMAIN IN PLACE ACROSS THE WRN
U.S. SATURDAY AS A MID-LEVEL JET MOVES NEWD ACROSS THE ROCKIES AND
NRN PLAINS. AT THE SFC...A LOW PRESSURE AREA IS FORECAST TO DEVELOP
IN THE LEE OF THE ROCKIES WITH A BROAD LOW-LEVEL JET STRENGTHENING
IN THE GREAT PLAINS. THE LOW-LEVEL JET SHOULD RESULT IN STRONG
MOISTURE ADVECTION ACROSS THE CNTRL AND NRN PLAINS WITH A MOIST AXIS
SETTING UP FROM THE MID-MO VALLEY NNWWD INTO ERN SD. MODEL FORECASTS
DEVELOP MODERATE TO STRONG INSTABILITY ALONG THIS CORRIDOR BY
SATURDAY AFTERNOON. HOWEVER...A STRONG CAPPING INVERSION IN PLACE
ACROSS THE WARM SECTOR SHOULD BE PROBLEMATIC FOR STORM INITIATION.
THE GREATEST CHANCE FOR INITIATION APPEARS TO BE ACROSS NRN SD AND
SE ND AS THE EXIT REGION OF THE MID-LEVEL JET PASSES BY DURING THE
EARLY EVENING. FORECAST SOUNDINGS NEAR ABERDEEN ON SATURDAY AT 03Z
SHOW ABOUT 50 KT OF DEEP LAYER SHEAR WITH STEEP MID-LEVEL LAPSE
RATES SUGGESTING ANY STORMS THAT CAN INITIATE SHOULD BECOME
SUPERCELLS AND HAVE A LARGE HAIL THREAT. A TORNADO THREAT WILL BE
POSSIBLE CONSIDERING THE LOW-LEVEL SHEAR ENVIRONMENT. THE
UNCERTAINTY IS TIMING OF INITIATION. IF THE CAP REMAINS STRONG
DURING THE EVENING...STORM DEVELOPMENT WOULD HOLD OFF UNTIL THE
OVERNIGHT PERIOD OR COULD TAKE PLACE FURTHER WEST.

...SRN APPALACHIAN MTNS...
AN UPPER-LEVEL RIDGE IS FORECAST TO BE IN PLACE ACROSS THE MS VALLEY
SATURDAY. WARMING SFC TEMPS ON THE ERN SIDE OF THE RIDGE SHOULD
RESULT IN AN AXIS OF MODERATE INSTABILITY ACROSS THE SRN APPALACHIAN
MTNS WHERE SCATTERED THUNDERSTORMS SHOULD INITIATE SATURDAY
AFTERNOON. FORECAST SOUNDINGS IN ERN TN AND NRN GA ON SATURDAY SHOW
ABOUT 30 KT OF DEEP LAYER SHEAR SUGGESTING THE STORM MODE SHOULD
REMAIN MULTICELLULAR. THE MAIN THREAT WOULD BE FOR MARGINAL WIND
GUSTS AS LOW-LEVEL LAPSE RATES STEEPEN DURING THE DAY.

..BROYLES.. 05/20/2010

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