SWODY2
SPC AC 091729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT SAT AUG 09 2008
VALID 101200Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF NRN AND CNTRL
HIGH PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF MID-ATLANTIC
AND DELAWARE RIVER VALLEY...
...NRN AND CNTRL HIGH PLAINS...
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE ACROSS THE PACIFIC
NORTHWEST TONIGHT INTO SUNDAY AS AN UPPER-LEVEL RIDGE REMAINS IN
PLACE ACROSS THE NRN HIGH PLAINS. A LEE SFC TROUGH SHOULD BECOME
MORE DEFINED FROM ERN MT SWD INTO ERN WY WITH MODEL FORECASTS
DEVELOPING MODERATE INSTABILITY FROM THE TROUGH EWD ACROSS THE WRN
DAKOTAS AND WRN NEB. DIFFLUENT FLOW ALOFT...SFC HEATING AND
LOW-LEVEL CONVERGENCE AHEAD OF THE SFC TROUGH SHOULD ALLOW SCATTERED
THUNDERSTORMS TO DEVELOP ALONG THE INSTABILITY AXIS DURING THE
AFTERNOON WITH CONVECTION PERSISTING INTO THE EVENING.
FORECAST SOUNDINGS ALONG THE INSTABILITY AXIS AT 21Z SHOW MODERATE
VERTICAL SHEAR PROFILES IN PLACE BY MID-AFTERNOON LARGELY DUE TO
VEERING WINDS BELOW 700 MB AND SPEED SHEAR IN THE MID-LEVELS. WITH
0-6 KM SHEAR VALUES IN THE 25 TO 35 KT RANGE...SHEAR SHOULD BE
SUFFICIENT FOR SEVERE MULTICELLS. AN ISOLATED SUPERCELL MAY ALSO
OCCUR WHERE STORMS HAVE ACCESS TO LOCALLY MAXIMIZED INSTABILITY.
ISOLATED LARGE HAIL THREAT MAY EXIST PARTLY DUE TO THE STEEP
MID-LEVEL LAPSE RATES EVIDENT ON FORECAST SOUNDINGS. WIND DAMAGE
WILL ALSO BE POSSIBLE ESPECIALLY IF A BOWING LINE SEGMENT CAN
ORGANIZE AND PERSIST INTO THE EARLY EVENING.
...MID-ATLANTIC/DELAWARE RIVER VALLEY...
AN UPPER-LEVEL LOW WILL DRIFT SEWD ACROSS THE ERN GREAT LAKES REGION
TONIGHT INTO SUNDAY. AT THE SFC...A COLD FRONT WILL MOVE EWD ACROSS
CNTRL NY...CNTRL PA AND THE MID-ATLANTIC. AHEAD OF THE
BOUNDARY...SUBSTANTIAL DESTABILIZATION SHOULD OCCUR WITH THE
DEVELOPMENT OF NUMEROUS THUNDERSTORMS ALONG THE COAST FROM SRN NEW
ENGLAND SWD INTO ERN VA AROUND MIDDAY. THUNDERSTORMS SHOULD PERSIST
INTO THE LATE AFTERNOON WITH THE CONVECTION GRADUALLY MOVING
OFFSHORE DURING THE EVENING.
CONCERNING THE SHEAR ENVIRONMENT...A 45 TO 55 KT MID-LEVEL JET
ROUNDING THE BASE OF THE UPPER-LEVEL TROUGH WILL HELP TO CREATE
MODERATE TO STRONG VERTICAL SHEAR PROFILES ACROSS THE REGION SUNDAY.
THIS SHOULD SUPPORT SEVERE MULTICELLS AND ISOLATED SUPERCELLS IN THE
EARLY AFTERNOON. FORECAST SOUNDINGS STEEPEN LOW-LEVEL LAPSE RATES
QUICKLY ACROSS THE REGION BY MIDDAY SUGGESTING WIND DAMAGE WILL BE
POSSIBLE WITH THE STRONGER CELLS AND BETTER ORGANIZED LINE SEGMENTS.
ALTHOUGH MID-LEVEL LAPSE RATES WILL NOT BE THAT STEEP...COLD AIR
ALOFT /500 MB TEMPS OF -14 TO -16C/ ALONG WITH THE SHEAR MAY BE
SUFFICIENT FOR ISOLATED LARGE HAIL ESPECIALLY IF SUPERCELLS CAN
DEVELOP.
...SRN PLAINS/SRN AND CNTRL ROCKIES...
AN UPPER-LEVEL RIDGE IS FORECAST TO BE IN PLACE FROM THE FOUR
CORNERS REGION EXTENDING NEWD INTO THE CNTRL AND NRN PLAINS.
NORTHWEST FLOW WILL EXIST ACROSS THE SRN PLAINS WHERE MODEL
FORECASTS SHOW AN AXIS OF INSTABILITY EXTENDING FROM ERN NM EWD
ACROSS WEST TX INTO OK SUNDAY. SCATTERED THUNDERSTORMS SHOULD
DEVELOP SUNDAY AFTERNOON AS SFC TEMPS WARM AND A CAPPING INVERSION
DIMINISHES. ALTHOUGH MID-LEVEL TEMPS ARE FORECAST TO BE QUITE WARM
...FORECAST SOUNDINGS SHOW ENOUGH VERTICAL SHEAR FOR A MARGINAL
SEVERE THREAT. STRONG WIND GUSTS AND HAIL WILL BE POSSIBLE IN THE
LATE AFTERNOON WITH THE STRONGER MULTICELLS WHEN INSTABILITY WILL BE
MAXIMIZED AND LOW-LEVEL LAPSE RATES WILL BE QUITE STEEP.
..BROYLES.. 08/09/2008
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