Severe Thunderstorm Warning 191, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD
250 PM CDT FRI AUG 30 2002

MAIN FORECAST CHALLENGES ARE SEVERE WEATHER CHANCES TONIGHT...THEN
PRECIP CHANCES THROUGH SUNDAY. DECENT VORT MAX NOW SPINNING OVER
MONTANA AND THE WESTERN PORTIONS OF THE DAKOTAS...AS WELL AS A
SURFACE TROUGH SITUATED OVER THE WESTERN DAKOTAS. NUMEROUS CLOUDS
AND SCATTERED SHOWERS AND THUNDERSTORMS LINGERED OVER THE EASTERN
DAKOTAS MUCH OF THE DAY...WHICH PUT A DAMPER ON HEATING.
HOWEVER...THE WESTERN PORTION OF THE CWA CLEARED OUT BY EARLY
AFTERNOON...AND TEMPERATURES HAVE NOW PUSHED WELL INTO THE 80S.
MODELS INDICATING GOOD MOISTURE CONVERGENCE AND INCREASING
INSTABILITIES IN THAT AREA...WHICH FITS IN WITH WHERE A SEVERE
THUNDERSTORM WATCH HAS BEEN ISSUED. WILL GO WITH LIKELY POPS. WITH
SOME SHOWERS STILL OCCURRING IN THE FAR EASTERN CWA AS WELL...WILL
KEEP SCATTERED POPS MENTIONED. THIS SYSTEM WILL MOVE OFF TO THE
NORTHEAST OVERNIGHT...WITH PRECIP CHANCES LOWERING SIGNIFICANTLY.

THE NEXT SHORTWAVE TROUGH TO AFFECT THE AREA WILL PUSH INTO MONTANA
ON SATURDAY...WHILE A COLD FRONT SLIDES TO FAR NORTHERN SOUTH
DAKOTA. WITH DECENT SOUTHERLY FLOW AHEAD OF THIS FRONT...THE MOIST
UNSTABLE AIRMASS WILL REMAIN IN PLACE...AND WILL WARRANT THE
POSSIBILITY OF THUNDERSTORMS DEVELOPING IN THE AFTERNOON. WILL THEN
KEEP A SMALL POP GOING ALL THE WAY THROUGH SUNDAY AS THE COLD FRONT
INCHES ITS WAY INTO THE CWA BEFORE WEAKENING AS IT EXITS SUNDAY
AFTERNOON.

BY SUNDAY NIGHT...THE UPPER FLOW BECOMES NEARLY ZONAL WITH ANY
ENERGY REMAINING WELL NORTH IN CANADA. A WEAK FRONT MAKES AN ATTEMPT
AT BACKDOORING INTO THE NORTHERN PART OF THE CWA ON MONDAY...BUT
BOTH ETA AND AVN WINDS AND H85 TEMPS INDICATE IT WILL NOT MAKE IT.
THEREFORE...WILL LEAVE CONDITIONS DRY FROM SUNDAY NIGHT INTO MONDAY
NIGHT...WHEN WEAK HIGH PRESSURE TAKES OVER.

.EXTENDED DISCUSSION...
EXTENDED MODELS ARE IN GENERAL AGREEMENT THROUGH THURSDAY...THEN
BEGIN TO SHOW SOME DIFFERENCES. UP TIL THURSDAY...RIDGING PATTERN
RETURNS TO NORTHERN PLAINS AS TROFING TAKES PLACE ACROSS THE WESTERN
CONUS. RIDGE AXIS MOVES EAST OF CWA ON WEDNESDAY WITH AMPLE RETURN
FLOW SETTING UP. LOLEVEL FLOW IS IMPRESSIVE ON THE AVN. THE
CANADIAN...NOGAPS AND ECMWF ALL AGREE WITH RIDGE AXIS PASSAGE ON
WEDNESDAY. SOME MINOR WAVES SLIDE OVER THE AREA WITH THE PASSAGE OF
THE RIDGE AXIS...BUT NOT TOO MUCH TO GET CONCERNED OVER. AVN SHOWS
SOME LIGHT QPF DEVELOPING TUESDAY EVENING AND CONTS THROUGH WED
AFTN. FOR NOW HAVE CHOSEN TO IGNORE AND KEEP DRY FCST GOING.

FOR THURSDAY AND FRIDAY...DIFFERENCES SHOW UP. THE AVN IS MOST
AGGRESSIVE WITH TROF EJECTION ON THURSDAY WITH SFC BOUNDARY SETTING
UP AND MOVING EAST DURING THE DAY. GOOD THETA-E RIDGE SETS UP
POINTING TO FAIR CONVECTIVE EVENT.  HOWEVER...THE CANADIAN...NOGAPS
AND ECMWF ARE A BIT SLOWER WITH WRN CONUS LOW. GIVEN PERFORMANCE OF
MRF WITH SPEED OF LAST SYSTEM AND STRENGTH OF JET ASSOCIATED WITH
DIGGING SYSTEM...LEANED TOWARD SLOWER SOLNS OF CANADIAN...NOGAPS AND
ECMWF.

TEMP WISE...GUIDANCE APPEARS TOO LOW TUESDAY AND WEDNESDAY...GIVEN
8H AND 7H TEMPS...RISING HEIGHTS AND SOUTHERLY FLOW. HAVE UPPED THEM
AROUND 5 DEGREES IN GRIDS. FOR THURSDAY AND FRIDAY...THEY ALSO SEEM
A TAD TO LOW SO WENT 3 TO 5 DEGREES HIGHER.

.ABR...NONE.

PARKIN/HINTZ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ABERDEEN, SD
807 PM CDT FRI AUG 30 2002

TIME(CDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0800 PM    7 E GETTYSBURG            SD   1.25 INCH HAIL
08/30/02   POTTER

NDM