Severe Thunderstorm Warning 152, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
345 PM CDT THU JUL 8 1999

CDFNT CONTINUES TO SLIP THRU CWA AT MIDAFTN...BECOMING DEFINED BY
CU LN ON VSBL STL LOOP...FM NR KMML...TO JUST E OF KYKN...TO N OF
KODX.  SRN END OF FNT HAS NOT PROGRESSED A LOT...LAYING OUT MORE
E TO W AS UPPR FORCING SHEARS ENE.  PRIOR BACKDOOR OUTFLOW INTO
ERN CWA HAS MIXED OUT IN STG SW LLJ INDICATED ON PROFILERS.  STLT
SOUNDER AND MSAS AGREE AS WELL ON MORE UNSTABLE AIR ACRS WCNTRL IA.
MAIN CONCERN FOR THIS PACKAGE WILL BE IN FIRST 6HRS...THEN OVERALL
NOT A VERY EVENTFUL FORECAST.

PLAYING A WAITING GAME FOR POTENTIAL EXPLOSIVE DEVELOPMENT.  WIND
FIELDS ARE NOT ALL THAT FAVORABLE FOR SVR WITH LIMITED SHEAR...
RATHER IS DEPENDENT ON INSTABILITY...WHICH IS NRG 3500 J/KG.  RUC IS
TRACKING FEATURES VERY WELL THUS FAR.  PROGGED SOUNDINGS A LITLLE
TOO COOL...BUT EVEN WARMED...A SMALL CIN OF 50-65 J/KG EXISTS OVR NW
IA COUNTIES.  WOULD BELIEVE THAT DEEP LOW LVL CONVERGENCE ALG FNT
SHOULD BE ENOUGH TO SET OFF AT LEAST SCATTERED ACTIVITY.  LARGER
SCALE FORCING REALLY HARD TO COME BY...BUT WOULD BE MARGINALLY
BETTER ARND MJQ/EST INTO ERLY EVNG.  WL PLAY STRONGEST POPS IN FAR
ERN AND SERN CWA. MAY BE CHC OF A PULSY SVR STM WITH MARGINAL
HAIL...OR PERHAPS A BIT OF WIND AS DRIER AIR WORKS EWRD.  OTHER
QUESTION IS HOW FAR WWRD TO MNTN PCPN.  WV LOOP SHOWING WK MSTR
PLUME SW TO NE ACRS SD...AND WL BE CHC ALG BOTH LEADING AND TRAILING
EDGE FOR A ROGUE STORM TO POP UP.

OTHERWISE...ONLY REAL INTEREST COMES ON FRIDAY...STG CAA SETUP AS
VORTEX SHEARS INTO MN DURG DAY.  WL BE WELL MIXED AT LOW LVLS
AGAIN...AND ETA SUGGESTS THAT ALG EDGE OF MID LVL CD CORE SOME LOW
TOPPED CONVECTION IS PSBL WITH ARND 100 J KG AFTN CAPES WITH SFC
TMPS REACHING MID TO UPPR 70S...NE OF KHON...KFSD...KSPW LN.  WL ADD
IN SCT AFTN SHOWERS THERE...BUT HOLD OFF ON TSRA FOR NOW.

HAVE NOTICED THE AVN WARM BIAS MENTIONED IN NATIONAL DISC...SO WL
IGNORE AND TREND TMPS TO NGM AND ETA PREFERRED MIX OUT TMPS FOR
FRI.  OTHER TMPS WL USE GENERALLY ETA FOR GUIDANCE...BUT MODERATE
THE COOLISH 8H TMPS A BIT UPWARD...SOMEWHAT CLOSER TO NGM.

FOR THE EXTENDED PACKAGE...REGION REMAINS LARGELY ON ANTICYLONIC SIDE
OF MIDLVL WNW FLOW...WITH MOST EXTENDED GUIDANCE SUPRISINGLY CLOSE ON
TIMING OF SUBTLE WAVE CROSSING AREA SUN NGT.  PRECIPITATION FORCING
WILL BE LARGELY ON THE MESOSCALE...SO FOR NOW WILL ONLY FAVOR THE
NOCTURNAL TIMING ON SUN NGT/MON AM.  WARMEST DAY WOULD APPEAR TO BE
MONDAY...ESPLY SRN AND ERN CWA...BEING SOMEWHAT PREFRONTAL.  BNDRY
REALLY NOT GOING ANYWHERE ON TUE...SO AGAIN SIMILAR TO SLIGHLY LWR
TMPS.

.FSD...NONE
CHAPMAN