000 
FXUS63 KUNR 072002
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
202 PM MDT MON SEP 7 2009

.DISCUSSION...CURRENT WATER VAPOR IMAGERY SHOWS TROUGH OVER THE
NORTHWESTERN CONUS WITH RIDGE STRETCHING FROM EASTERN NEBRASKA
INTO ONTARIO. COLD FRONT CURRENTLY LOCATED FROM PERKINS COUNTY TO
SHANNON COUNTY WILL STALL OVERNIGHT. SHOWERS AND THUNDERSTORMS
DEVELOPING BEHIND THE FRONT WILL BECOME MORE WIDESPREAD THIS
EVENING AND OVERNIGHT AS A SERIES OF SUBTLE SHORTWAVES MOVE ACROSS
THE CWA. AT THIS TIME IT APPEARS THE HEAVIEST PRECIPITATION WILL
BE FOUND ACROSS NORTHERN PORTIONS OF NORTHEAST WYOMING AS WELL AS
FAR NORTHWEST SOUTH DAKOTA.

ON TUESDAY...TROUGH WILL SWING ACROSS THE CWA AS COLD FRONT
BEGINS TO PROGRESS EASTWARD. EXPECT SHOWERS AND THUNDERSTORMS TO
DEVELOP ACROSS MUCH OF THE CWA AS THE TROUGH MOVES ACROSS THE
REGION. INSTABILITY AND SHEAR WILL INCREASE ACROSS SOUTH CENTRAL
SOUTH DAKOTA ALONG AND AHEAD OF THE FRONT. EXPECT CAPE VALUES
AROUND 2000 J/KG ACROSS TODD...TRIPP...AND MELLETTE COUNTIES.
AT THIS TIME SHEAR APPEARS MARGINAL FOR SEVERE THUNDERSTORMS...BUT
GIVEN THE MAGNITUDE OF THE INSTABILITY...A FEW STORMS COULD
BECOME SEVERE WITH LARGE HAIL AND DAMAGING WIND GUSTS.

ON WEDNESDAY...SHOWERS AND THUNDERSTORMS WILL LINGER IN SOUTH
CENTRAL SOUTH DAKOTA EARLY. EXPECT CLOUDS TO DIMINISH ACROSS THE
AREA AS WEAK HIGH PRESSURE ALOFT BUILDS ACROSS THE CWA. 

EXTENDED...MODELS CONTINUE TO BRING AN UPPER LEVEL LOW INTO THE 
NORTHERN PLAINS FOR THE END OF THE WORK WEEK INTO THE WEEKEND. HAVE 
INTRODUCED POPS TO MOST AREAS THROUGH THIS PERIOD SINCE MODELS HAVE 
BEEN PERSISTENT WITH BRINGING THIS FEATURE THROUGH THE REGION OVER 
THE PAST FEW RUNS.  MODELS HAVE PREVIOUSLY BEEN SLOWLY MOVING THIS 
FEATURE WESTWARD...SO WILL HAVE TO KEEP AN EYE ON THIS OVER THIS 
NEXT FEW RUNS TO SEE IF MODELS HAVE STABILIZED.

&&

.AVIATION...SHOWERS AND THUNDERSTORMS ARE EXPECTED...MAINLY LATE 
THIS AFTERNOON THROUGH TONIGHT...BRINGING AREAS OF MVFR VIS/CIGS. 
THE BEST CHANCES WILL BE ACROSS NORTHEAST WYOMING AND NORTHWESTERN 
SOUTH DAKOTA. OTHERWISE...VFR CONDITIONS ARE EXPECTED.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

JRW/JS