SWODY1
SPC AC 211254
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0754 AM CDT SUN SEP 21 2008
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EARLY TONIGHT
ACROSS THE NRN/CENTRAL HIGH PLAINS...
...CENTRAL/NRN HIGH PLAINS THIS AFTERNOON INTO EARLY TONIGHT...
A MID LEVEL SHORTWAVE TROUGH EXTENDING FROM WRN WY TO WRN MT THIS
MORNING WILL EJECT NEWD OVER THE NRN HIGH PLAINS THROUGH
TONIGHT...WHILE AN UPSTREAM WAVE OFF THE ORE/NW CA COASTS MOVES EWD
TO NRN NV BY THE END OF THE PERIOD. A SURFACE LEE TROUGH WILL
PROGRESS EWD FROM ERN MT/WY TO THE WRN DAKOTAS/NEB BY TONIGHT...WITH
WEAK CYCLOGENESIS POSSIBLE INVOF NW SD. THE LEE TROUGHING AND THE
APPROACH OF THE INITIAL SHORTWAVE TROUGH WILL HELP MAINTAIN A 35-50
KT SLY LLJ ACROSS THE CENTRAL/NRN PLAINS THROUGH TONIGHT.
THE LOW-LEVEL SLY/SSELY FLOW ACROSS THE CENTRAL/NRN PLAINS WILL
TRANSPORT BOUNDARY LAYER DEWPOINTS OF 55-60 F NWD BENEATH A PLUME OF
STEEP MID LEVEL LAPSE RATES FROM THE NRN AND CENTRAL ROCKIES. THIS
LOW-LEVEL MOISTURE AND AFTERNOON SURFACE TEMPERATURES IN RANGE OF
75-80 F WILL CONTRIBUTE TO MLCAPE VALUES OF 1000-1500 J/KG. DEEP
LAYER VERTICAL SHEAR WILL INCREASE DURING THE DAY /ESPECIALLY OVER
WRN SD AND NEB/ WITH THE APPROACH OF THE LEAD SHORTWAVE
TROUGH...WHILE THE LLJ WILL CONTRIBUTE TO SUBSTANTIAL LOW-LEVEL
SHEAR THIS AFTERNOON INTO TONIGHT. THE COMBINATION OF MODERATE
INSTABILITY AND VERTICAL SHEAR SHOULD BE SUFFICIENT FOR A COUPLE OF
SUPERCELLS CAPABLE OF PRODUCING AT LEAST ISOLATED LARGE HAIL AND
DAMAGING GUSTS. CONVECTION WILL LIKELY EVOLVE INTO A COUPLE OF
CLUSTERS BY THIS EVENING IN CONJUNCTION WITH STRENGTHENING LOW-LEVEL
WAA...THOUGH DIMINISHING INSTABILITY WILL TEND TO REDUCE THE SEVERE
STORM THREAT OVERNIGHT.
...ELSEWHERE...
WIDELY SCATTERED THUNDERSTORMS CAN BE EXPECTED AGAIN TODAY FROM
MO/IL SWD TO LA/MS IN ASSOCIATION WITH A WEAK MID LEVEL TROUGH AND A
CORRIDOR OF LOW-MID 60S BOUNDARY LAYER DEWPOINTS. A PLUME OF RICHER
MOISTURE EXTENDS ENEWD FROM THE CENTRAL/NRN GULF OF MEXICO TO
FL...ALONG AND S OF A RESIDUAL/DIFFUSE BAROCLINIC ZONE. SCATTERED
THUNDERSTORMS WILL BE POSSIBLE TODAY WITHIN THIS MOIST AND
MODERATELY UNSTABLE ENVIRONMENT OVER FL.
..THOMPSON/SMITH.. 09/21/2008
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