343 
FXUS63 KFSD 222012
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
315 PM CDT THU AUG 22 2002

SYNOPSIS...MORNING SUBJECTIVE UPPER AIR ANALYSIS INDICATED BROAD 
TROUGH ACROSS THE WESTERN US WITH RIDGING CONTINUING INTO THE SE. AT 
H3 50 TO 60 KNT JET WAS CYCLONICALLY CURVED INTO THE CNTRL PLAINS 
WITH THE LEFT FRONT EXIT REGION IN N-CNTRL SD. SEVERAL SHORT WAVES 
WERE ANALYZED THIS MORNING MOVING NE IN THE SOUTHWEST FLOW. THE 
FIRST WAS OVER WRN NEB/NE CO...WITH THE SECOND ASSOCIATED WITH A GOOD 
THERMAL TROUGH IN NM. LOW LEVEL MOISTURE REMAINED IN ABUNDANCE 
ACROSS THE REGION WITH PWATS RUNNING CLOSE TO 2 INCHES. 18Z 
OBJECTIVE SFC ANALYSIS INDICATED A COMPLICATED SFC PATTERN WITH 
SEVERAL OUTFLOW BOUNDARIES.

FORECAST...ANOTHER FUN FORECAST THIS AFTERNOON IN TRYING TO TIME AND 
PLACE THE BEST CHANCES FOR CONVECTION. AS MENTIONED ABOVE ATMOSPHERE 
IS MOIST...AND IS SOMEWHAT UNSTABLE. WITH MID LEVELS COOLING...BUT 
LIMITED LOW LEVEL HEATING...50MB MLCAPE RUNNING UNDER 1500 J/KG. 
CONVECTIVE INHIBITION IS WEAK AGAIN AND WITH CONVERGENCE ALONG ANY 
OUTFLOW BOUNDARY COULD SEE AN ISOLATED STORM POP UP. WITH MID LEVEL 
COOLING...AN ISOLATED LARGE HAIL IS POSSIBLE. BEST CHANCES FOR 
INITIATION WILL BE IN STRONGEST CONVERGENCE ZONE OVER NE NEB. CLOUDS 
WILL FINALLY START TO DECREASE LATE TONIGHT AS DRIER AIR MOVES IN 
FROM THE WEST. THIS TREND WILL CONTINUE INTO FRIDAY...BUT WILL HAVE 
A GOOD CU FIELD DEVELOPING IN NW IA/SW MN WHERE GREATEST LOW LEVEL 
MOISTURE REMAINS. 

UPSLOPE FLOW WILL RETURN ON FRIDAY AFTERNOON OUT WEST AND MAY BE 
RESPONSIBLE FOR TRW BY LATE AFTERNOON. WILL INCLUDE SOME LATE NIGHT 
TRW FROM ANY COMPLEX THAT MIGHT GET GOING OUT WEST AND MOVE 
SOUTHEAST OVERNIGHT. THIS WILL LINGER INTO SATURDAY MORNING. 
OTHERWISE WITH THE PRESENCE OF THE FRONT TO THE SOUTHWEST...AND 
CONTINUED ISENTROPIC LIFT OVER THE FRONT...CLOUDS WILL BE HARD TO 
GET RID OF OUT WEST AND WILL COOL OFF TEMPS FOR SATURDAY AND SUNDAY. 
WILL NOT INCLUDE A CHC FOR RW/TRW ON SUNDAY AT THIS POINT DUE TO 
MODEL INCONSTANCY. 

EXTENDED...IN THE LARGE SCALE...THE MODELS ARE SIMILAR WITH A RIDGE 
OVER THE SRN PLAINS AND WEAK WAVES MOVING OVER THE RIDGE ACROSS THE 
NORTHERN PLAINS.  WHILE THERE ARE DIFFERENCES IN THE STRENGTH OF THE 
WAVE...ALL MODELS SHOW A WAVE MOVING ACRS TUESDAY WITH A SURFACE 
FRONT MOVING THROUGH THE EASTERN DAKOTAS INTO IA AND MN.  WITH SRLY 
FLOW ON THE BACK SIDE OF THE HIGH BEGINNING ON MONDAY...MSTR WL 
RETURN.  WITH WAVE APPROACHING ON TUE...EXPECT CHC OF WAA TSRA IN 
THE FAR WRN CWA LATE MONDAY NIGHT.  LIKELY SCT-BKN CLOUDS ON TUE WL 
MEAN TEMPS ONLY INTO THE L80S.  WITH 700 MB TEMPS BLO +10 EXPECT WL 
PUT IN CHC TSRA ACRS THE ENTIRE CWA ON TUE AND EXTEND INTO WED 
MORNING IN NW IA.  AFTER WAVE MOVES THROUGH...TEMPS WL COOL BACK TO 
THE 70S WITH A LITTLE DRIER AIR MOVING IN FOR LATE WED AND THU.

.FSD...NONE

BOUSTEAD/SCHUMACHER