000 
FXUS63 KFSD 062147
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD 
355 PM CDT THU JUN 6 2002

CONVECTION IS AT FOREFRONT OF CONCERN.  NOT TO GLOSS OVER ACTIVITY 
TONIGHT...BUT POTENTIAL FOR SIGNIFICANT SEVERE WEATHER/HEAVY RAINFALL
LATE FRIDAY AFTERNOON INTO SATURDAY MORNING AT FOREFRONT OF CONCERN.

STG IMPULSE IN UPR LVLS CRASHING THRU ND ATTM...DRIVING CDFNT EWARD
AND LESS SWRD THRU SD ATTM. SRN END REALLY COMING TO A CRAWL. TEMPS 
AND DEWPOINTS LEADING IN LOWER 90S/LOWER 50S ARE SUCH THAT LTL IF 
ANY INHIBITION TO CONVECTION EXISTS...ALLOWING SCT AT BEST TSRA
THIS EVENING WITH MSTR THE OBVIOUS LIMITING FACTOR. STORMS WILL BE
VERY HIGH BASED...AND ISOLATED HAIL OR GUSTY WINDS ARE ONLY MINIMAL
SEVERE THREAT. ANOTHER WK IMPULSE MOVES ACRS NRN PARTS OF SD LATE
TONIGHT...AND RESIDUAL BOUNDARY MAY FIRE A STORM OR TWO WITH LLJ.

FRONTAL POSITION OH SO IMPORTANT FOR FRIDAY. EVEN A MODEST PROFILE 
OF WIND/SHEAR MAKES TOMORROW A REAL SEVERE THREAT...AS WKLY CAPPED 
INTO AFTN...ALLOWING MSTR POOLING TO EARN ESTIMATED CAPES OF 
2500-3000 J/KG...BEFORE FRONTAL DYNAMICS TAKE CONTROL. SOME ELEVATED 
TSRA N OF SFC BNDRY LKLY ENTICED AS WK PV IMPULSE MOVES INTO NCNTRL 
SD BY MIDDAY. THIS WL BE LITTLE MORE THAN PRELUDE TO EVENING 
CONVECTION.  ALL SIGNS ARE FOR SCT SVR IN EVNG...THEN CLASSIC FOR 
BACKBUILDING MCS ALG FRONTAL BOUNDARY AS BETTER LOW LVL FEED 
RETREATS WWRD AND FOCUSES INTO SCNTRL SD TOWARD MIDNIGHT...BEFORE 
ONCE AGAIN VEERING EWRD.  PWATS ARE LITTLE LOWER THAN LIKE TO 
SEE...BUT FEEL THAT HEAVY REPEATED RAINS ARE THREAT AND WL PUT 
MENTION IN ZONES FOR FRI NIGHT.  WHILE LCL IS SOMEWHAT HIGH INITIALLY
LOWERING LCLS WITH TIME COULD MAKE FOR TORNADIC THREAT AS WELL LATE 
AFTERNOON AND EVENING.  CONFIDENCE IN SEVERE THREAT INCREASING WITH
MDLS CONVERGING ON BNDRY THRU CWA...AND NOT TOO DEPENDENT ON ACTIVITY
TONIGHT TO CONTROL POSITION.

FOR NOW...SUBSCRIBE TO THEORY THAT WARMING OF TMPS ALFT ON SAT WL
PUT END TO MORNING LINGERING CONVECTION FAVORING N AND E CWA...
THEN CAP OFF CHC FOR FESTERING BOUNDARIES TO FIRE UP LTR. THIS
CAPPED STATE IS LKLY TO LAST WELL INTO SUNDAY...BEFORE WK IMPULSE
IN SLY FLOW MOVES ALG FRONTAL BNDRY TO W TO ENTICE A FEW TSRA TO 
AT LEAST JAMES VLY SUNDAY NIGHT. HARD TO BELIEVE BASED ON JET THAT
FRONT WL BE AS FAR E ON SUNDAY NIGHT AS AVN PROGS.

TMPS WELL ABV GUIDANCE FOR MOST PART...BUT WL ALLOW FOR SIG 
CONVECTIVE DEBRIS TO HOLD TMPS BACK SAT ACRS N AND NE CWA.  IF ETA 
IS FULLY ACCURATE FOR LOW LVL THERMAL FIELDS ON SUN...100 NOT OUT OF 
QUESTION FOR SCNTRL AND LOWER MO RVR AREAS. NEVERTHELESS...SUMMERLIKE 
HEAT AND HUMIDITY WILL BE WITH US THIS WEEKEND.

IN THE EXTENDED RANGE...MAIN FEATURE OF INTEREST IS THE PASSAGE OF
THE INTERMOUNTAIN TROUGH...AFTER WHICH...REPOSITIONING OF LOW LATITUDE
RIDGE ADVERTISED IN ALL LONG RANGE MDLS FM SE TO SW US SHUD KEEP 
MAINLY DRY...WITH TMPS WARMING LATE WEEK.  LIFTING THE ENTIRE TROUGH 
NORTHEAST WITH SUCH A DRASTIC NEGATIVE TILT APPEARS A BIT OVERDONE 
IN MRF...WHICH IS ONE OF MOST AMPLIFIED OF ENSEMBLE MEMBERS WITH ERN 
RIDGE...AND ONE OF MOST PROGRESSIVE IN LATER TERM.  UKMET/ECMWF/CANADIAN
ARE FAIRLY CONSISTENT IN STYLE...BUT VARY IN TIMING.  AS MENTIONED...
LTST AVN/CANADIAN MUCH MORE AGGRESSIVE WITH EWRD MOVEMENT OF TROUGH/ 
FRONT BY LTR SUNDAY INTO HEART OF CWA.  BASED ON UPR PATTERN AND 
WITH RELATIVE JET/TROUGH POSITION...SEEMS QUITE UNREASONABLE TO SIDE
WITH THE RAPIDITY...AND WL KEEP SOMEWHAT SLOWER IN LINE WITH CRNT 
FCST.  SUN NIGHT...TSRA LIKELY TO IMPINGE ON FAR WRN CWA...WITH CHC
FARTHER E THRU SD CWA...AND RETAIN DRY E AS WL BE VERY FRONTALLY 
CONFINED WITH STG CAPPING PRECEDING BNDRY.  THIS WHOLE TREND IN PCPN
SHUD SHIFT W TO E WITH MAIN TROUGH. POTENTIAL FOR FAIRLY POTENT 
JET/FRONT INTERACTION ON MONDAY AS RIDGE BREAKS DOWN...AND COULD BE 
VERY INTERESTING FOR FSD CWA IF SLOWER THAN AVN/MRF.  LOWER DIRUNAL 
TEMP RANGE W MONDAY...SOMEWHAT GREATER E.  AVN/MRF REALLY WRAP UP 
LOW...AND LINGER FAIRLY GOOD CHC OF FRONTOGENETIC/CYCLONIC SHRA INTO 
TUE.  EVEN WITH SLOWER ECMWF/UKMET...SECONDARY TROUGH PASSAGE IN 
EFFECT. SO FOR NOW...WL LIMIT MENTION TO NRN AREAS AS IS NEW TO 
FCST.  REMOTE CHC OF SOMETHING ELEVATED BY THU...OTHERWISE DRY IN 
LARGE SCALE TRANSITION...WITH MODERATING TMPS.

.FSD...NONE
CHAPMAN