Severe Thunderstorm Warning 234, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
305 PM CDT SAT AUG 3 2002

PRELIMS WILL PROBABLY BE A LITTLE LATE AS THEY HASH OUT THE WATCH
BOX. MAIN PROBLEMS WITH FCST PKG IS IN THE SHORT TERM TNGT. WELL
ADVERTISED SFC TROF AND LOW PRES NOW TO THE EAST OF KPIR. IT LOOKS
LIKE THE 12Z ETA/MESO ETA IS WAY TOO FAST...AND PREFER THE OLDER
RUNS OF THE ETA/THE 12Z AVN AND RUC FOR FRONTAL TIMING. PLENTY OF
WAA AND JUICED UP SFC AIR HAS RETURNED TO THE FSD CWA...WITH MANY
LOCATIONS WELL INTO THE 90S...REACHING CONVECTIVE TEMPS. WIND SHEAR
BECOMES LIMITED IN TIME...AS PROFILES SHOW MORE OF A UNIDIRECTIONAL
FLOW THIS EVENING AS WELL AS SPEEDS WHICH ARE RATHER UNIFORM.
STILL...INSTABILITY IS HIGH ENUF THAT ONE CANNOT RULE OUT SVR WX
EARLY THIS EVENING...AND WELL WORD ACCORDINGLY. SO FAR...THE TS IS
STRAIGHT UP AND DOWN IN THE WRN CWA BUT THAT MAY CHANGE. MORE
CONCERNED ABOUT A HEAVY RAIN THREAT WITH SOME TRAINING ECHOES. THE
FIRST WAVE WHICH IS NOW WELL INTO MN IS SHOWING SOME HANGBACK
FEATURES TO IT INVOLVING VORT...AND A SECOND UPR WAVE WILL BE MOVG
IN OVERNIGHT FM CO. THIS SECOND WAVE WL CONT TO INTERACT WITH THE
SLOWLY SAGGING SOUTH BNDRY TO PRODUCE THAT HEAVY RAIN THREAT...MAINLY
FM I 90 SWD.

ON SUNDAY...SHRA AND A FEW TS ARE STILL A POSSIBILITY IN THE SOUTH.
ETA SHOWS THE CWA IN THE RIGHT REAR JET ENTRANCE RGN. BELIEVE THE
AVN IS SAGGING THE LOW LVL BNDRY TOO FAR TO THE SOUTH...AS AM NOT
SURE HOW IT CAN GO THAT FAR WITH THE UPPER RIDGE SO STRONG. SO AM
LEANING TOWARD THE ETA SOLN FOR LOW LVL FRONTAL PLACEMENT...ACTUALLY
ALL THE WAY INTO SUNDAY NIGHT AND MONDAY...WHEN IT LIFTS BACK TOWARD
THE CWA AS A WMFNT. PCPN CHCS WL CONT SUN NIGHT AND MON MORNING DUE
TO A LARGE AMOUNT OF MID LVL FRONTOGENESIS ALONG I 90...AND THE
STILL STRONG MID TO UPPER LEVEL PV/PV ADV REGIME IN THE AREA. THIS
DOES NOT CLEAR OUT OF HERE UNTIL LATE IN THE DAY ON MONDAY...ENDING
IN THE WEST OF COURSE FIRST.

LATER IN THE WEEK...MODELS STILL SHOW A KILLER RIDGE OVER THE MID
SECTION OF THE COUNTRY...WITH A GRTLKS HIGH PRES SYSTEM BACKING INTO
THE CWA ON TUE AND WED. MRF AND NEW 12Z AVN STILL SHOW A RIDGE RIDER
JUST TO THE WEST OF THE FSD CWA TUE NIGHT AND WED...AND LEFT OUT OF
ALL ZONES FOR NOW DUE TO LIKELY CAPPING. MRF/ECMWF THEN SHOW A
STRONGER WAVE MOVG THRU FRI NIGHT...SO THAT IS THE NEXT CHC FOR PCPN
AFTER MONDAY NIGHT.

.FSD...NONE