Severe Thunderstorm Warning 371, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
355 PM CDT WED AUG 28 2002

ENCOUNTERING THE SAME PROBLEMS LATE THIS AFTN AND ERLY EVE AS WE DID
YDAY. SFC RIDGING CONTS TO NUDGE INTO THE SE PART OF THE FSD CWA FM
HIGH PRES OVR THE GRTLKS. THEREFORE...NOT A LOT TO FOCUS ON IN THE
LOWER LEVELS AND WITH LITTLE IN THE WAY OF SHORTWVS ALOFT...NOT A
LOT OF FOCUS UP THERE EITHER. BUT WHAT WE DO HAVE IS A HIGH AMNT OF
DEEP MSTR AS EVIDENCED BY THIS MRNGS AREA SNDGS...AND NO CAPPING
PRESENT. WITH THE RELATIVELY COOL AIR ALOFT...+4 TO +6C AT 7H AND
-13C AT 5H AND HIGH AMNT OF MSTR...CONVECTIVE TEMPS ARE PRETY LOW IN
THE LOWER 80S. SO AIRMASS TS DEVELOPS...THEN DISSIPATES WITH THE HTG
ARND SUNSET. IN ADDN...ANY ONE OF THESE SMALL CELLS COULD PRODUCE A
GOOD 2 INCHES OF RAIN WITH ITS LITTLE OR NO MOVEMENT...WITH VERY WK
WIND SHEAR ONCE AGAIN PREVAILING. ATTM...IT APPEARS THAT THE MAIN
FOCUS OF ACTIVITY ONCE AGAIN APPEARS TO BE WHERE ANY TS DIED OFF
EARLIER TDAY...WHICH IS ARND ERN NEB UP TO KSUX...AND UP IN THE NWRN
PART OF THE CWA. IN ADDN...UPSLOPE ENHANCED BUFFALO RIDGE TS IS ALSO
GETTING GOING. SO THESE THREE AREAS MAY RECEIVE SOME TS ACTIVITY
WHICH IS MORE THAN ISOLD ERLY THIS EVE. FAIR AMNT OF PATCHY FOG
ARND LAST NIGHT AND WITH THE LIGHT S TO SE SFC FLOW CONTINUING TNGT
AND HIGH LOW LVL DEW PTS...REALLY CANNOT RULE OUT AGAIN SO WORDED
ACCORDINGLY.

ON THURSDAY...SAME SETUP AGAIN...EXCEPT THERE IS A LITTLE MORE
VEERING IN THE MESOETA SNDGS PROVIDING SOME DIR SHEAR...BUT AGAIN
VERY LIGHT SPEED SHEAR. THEREFORE EXPECT ANY TS ACTIVITY TO BUILD IN
THE LATE AFTN OR ERLY EVENING THEN DISSIPATE. PWATS REMAIN HIGH
THURSDAY...BASICALLY LIKE TDAY IN THE 1.25 TO 1.5 INCH RANGE SO ANY
RAIN FM THESE SLOW MOVERS COULD BE HEAVY.

WELL ADVERTISED MID LVL SHORTWV THEN MOVES INTO THE CWA ON FRIDAY.
THE ETA HAS FINALLY PICKED UP SOME RAIN WITH IT WITH THE INCREASING
LOW LVL JET AND OVERALL SPEED SHEAR INCREASES. WITH THE RELATIVELY
COOL AIR HANGING ARND ALOFT...WILL NEED TO WATCH THIS FOR ANY SVR TS
POTENTIAL DURING THE DAY AND EARLY EVE. THIS SYSTEM QUICKLY DEPARTS
FRI NIGHT AND MAINLY ONLY AFFECTS THE ERN CWA DURING THIS PD.

THE EXTENDED IS A MESS. THE 00Z MODELS LAST NIGHT BASICALLY PRINTED
A PICTURE OF WARM AND HUMID AIR THRU THE FIRST HALF OF NEXT WEEK...
WITH A ZONAL TO SW FLOW ALOFT. HOWEVER THE 12Z AVN CAME OUT VERY
DIFFERENT WITH MORE OF A COOLER PATTERN AND A NW FLOW ALOFT. THIS
COULD HAVE BEEN IGNORED...HOWEVER THE 84HR ETA IS NEARLY IDENTICAL
WITH THE 12Z 84HR AVN AT 7H AND 5H. IN FACT...THE 00Z RUN FROM
MONDAY NIGHT DID SHOW A COOLER NW FLOW ALOFT ERLY NEXT WEEK...SO AM
THINKING THE 00Z MODELS FM LAST NIGHT MAY NOT BE CORRECT. FM THE 12Z
AVN/12Z ETA...ONE CAN SEE A FAIRLY POTENT WAVE MOVG DOWN SAT
NIGHT...WHICH IS IN MT SAT AFTN. THEN ANOTHER STRONGER WAVE MOVES
THRU SUN NIGHT...WHICH YOU CAN SEE ON BOTH MODELS IN BRITISH COL SAT
AFTN. THIS LEAVES A NW FLOW WITH COOLER 850MB TEMPS. 12Z AVN
CONTINUED TO SHOW ANOTHER WAVE MOVG THRU NEXT WED SO FOLLOWED.

.FSD...NONE
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