Severe Thunderstorm Warning 131, NWS Aberdeen, SD

AREA FORECAST DISCUSSION FOR CENTRAL/N-EAST SD AND W-CENTRAL MN
NATIONAL WEATHER SERVICE ABERDEEN SD
323 PM CDT SAT AUG 3 2002

FORECAST CONCERN FOR TONIGHT WILL BE CHANCES FOR SEVERE WEATHER
EARLY THIS EVENING.  MODELS REMAIN CONSISTENT IN THE SHORT TERM AND
WITH TIMING OF SURFACE BOUNDARY TONIGHT.  PREFER THE ETA OUT TO 84
HOURS FOR THIS FORECAST WITH AVN CONTINUING CONVECTIVE SCALE
FEEDBACK ISSUES UPSTREAM OF UPPER RIDGE AXIS.

SURFACE ANALYSIS FROM 19Z SHOWS SLP MINIMUM ACROSS CENTRAL SOUTH
DAKOTA WITH WARM FRONTAL BOUNDARY STRETCHING SOUTHEAST FROM LOW INTO
SOUTHEAST SOUTH DAKOTA.  LAPS DATA INDICATING GREATEST INSTABILITY
ACROSS SOUTHEAST SOUTH DAKOTA WITH SURFACE BASED CAPES OF 2500-3000
J/KG.  PERSISTENT MID LEVEL CLOUD HAS ACTED TO LIMIT DESTABILIZATION
TO SOME DEGREE ACROSS SOUTHEAST CWA WHERE LIFTED INDICES RIGHT
AROUND 0 AND SURFACE BASED CAPES BETWEEN 500 AND 1000 J/KG.  CAP
WHICH HAD FORMED FROM WARM ADVECTION PATTERN HAS ERODED IN SOUTH
CENTRAL SOUTH DAKOTA AS SURFACE HEATING HAS BEEN MORE PREVALENT
THROUGH THIS AFTERNOON.  AS PROGRESS THROUGH LATE AFTERNOON...EXPECT
CONVECTION ACROSS SOUTH CENTRAL SOUTH DAKOTA TO MOVE NORTHEAST AND
POSSIBLY AFFECT FAR SOUTHERN AND SOUTHEASTERN COUNTIES.  18Z MESOETA
SHOWING WELL DEFINED 700 HPA SHORT WAVE ACROSS CENTRAL SOUTH
DAKOTA.  EXPECT LOW LEVEL LIFT DOWNSTREAM OF THIS WAVE TO BE ENOUGH
TO WEAKEN CAP ACROSS FAR SOUTHEAST CWA.  LAPS SOUNDING INDICATING
PERSISTENCE OF GOOD LOW LEVEL VEERING PROFILE WHICH ANY STORMS WILL
BE ABLE TO TAP INTO WITH 0-3 SRH OF AROUND 150.  RECENTLY ISSUED
TORNADO WATCH INCLUDES COUNTIES EAST OF KABR.  WITH 700 HPA TROUGH
MOVING EAST OF CWA THIS EVENING BEST LOW LEVEL SHEAR WILL MOVE INTO
CENTRAL MINNESOTA ALONG WITH BULK OF LOW LEVEL WARM AIR ADVECTION.

SURFACE HIGH BUILDS INTO AREA TONIGHT WITH WEAK LOW LEVEL COLD AIR
ADVECTION.  STILL FEEL THAT NORTH WINDS COULD APPROACH BREEZY
CATEGORY FOR A TIME BETWEEN 07-11Z ACROSS FAR NORTHEAST CWA WHERE
PRESSURE RISES WILL BE THE MOST SUBSTANTIAL.  WILL CLEAR RAPIDLY
TONIGHT AS SYNOPTIC SCALE MID LEVEL DVM MOVES INTO AREA WITH
APPROACH OF MID LEVEL RIDGING.  DEEP UPPER LOW FORECASTED TO MOVE
INTO NORTHERN ONTARIO BY SUNDAY EVENING AND UPPER WAVE PATTERN
REMAINS FAIRLY AMPLIFIED WITH MODELS CONTINUING TO SHOW MORE
PRONOUNCED UPPER RIDGING FROM SUNDAY NIGHT INTO MONDAY.  THUS...FEEL
THAT PRECIP PROSPECTS LOOKING LESS AND LESS PROMISING FOR SUNDAY
EVENING AND WILL REMOVE POPS EXCEPT FOR FAR NORTHWEST CWA.  MONDAY
AND TUESDAY LOOK TO BE DRY UNDER INFLUENCE OF UPPER RIDGE WITH NEXT
CHANCE OF TSRA LOOKING TO BE TUESDAY NIGHT AS EASTERN PACIFIC TROUGH
ACQUIRES MORE OF POSITIVE TILT AND SLIGHTLY WEAKENS UPPER RIDGE OVER
NORTHERN PLAINS.  THIS WILL ALLOW FOR BETTER CHANCE OF NOCTURNAL
CONVECTION TUESDAY NIGHT WITH WAA PATTERN FORMING DOWNSTREAM OF WEAK
UPPER SHORT WAVE.

.EXTENDED DISCUSSION...
5H RIDGE AXIS MOVES E OF CWA WITH SFC LOW MOVG IN FROM W. INCRGR
CLDS...TSTMS FOR WED AND FRI AS SHT WVS MOVE THRU DEPRESSING RDG.
OVERALL S TO SW FLOW...SO REASONABLE MSTR WITH THESE WVS. SAT SHOULD
BE DRY AS SFC WV MOVES OFF TO EAST.

.ABR...NONE

MARSILI/MARSHALL