Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 260848
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
348 AM CDT TUE AUG 26 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 346 AM CDT TUE AUG 26 2014

BAND OF CONVECTION ACROSS EASTERN NEBRASKA INTO WESTERN IOWA
ASSOCIATED WITH STRONG CONVERGENCE NEAR THE 925 HPA FRONT. THIS
BOUNDARY IS EXPECTED TO SLOWLY DRIFT NORTH...AND HAVE SEEN SOME
ENHANCEMENT ON THE WEST SIDE OF CONVECTIVE BAND AS A WEAK WAVE
APPROACHES FROM THE SOUTH WEST.  SOME OF THIS CONVECTION COULD
SCRAPE THE SIOUX CITY TO STORM LAKE PORTION OF THE FORECAST AREA
THROUGH 15Z OR SO...AND THEN EXPECT CONVECTION TO REALLY FALL APART
AS WAVE CONTINUES TO LIFT AWAY FROM THE AREA AND FORCING BECOMES
WEAK.  THERE AFTER...EXPECT MUCH OF THE DAYLIGHT HOURS TO BE
RELATIVELY QUIET BEFORE THE BOUNDARY REIGNITES TONIGHT.  HAVE NOT
MADE SIGNIFICANT CHANGES TO THE POPS...BUT HAVE SLOWED TIMING SOME
AS THE PATTERN CONTINUES TO SLOW IN ITS EVOLUTION.  WITH
THAT...STILL KEPT FAIRLY STRONG POPS ESPECIALLY SOUTH OF I 90
TONIGHT. MOST ORGANIZED CHANCES FOR PRECIPITATION APPEAR TO BE AFTER
06Z...AS ANOTHER SHORT WAVE LIFTS NORTHEAST INTERACTING WITH THE
STATIONARY BOUNDARY.  AS HAS BEEN ADVERTISED FOR DAYS...AM CONCERNED
ABOUT POTENTIAL FOR FLASH FLOODING DUE TO TRAINING OF STORMS ALONG
THE BOUNDARY.  STILL HARD TO NARROW DOWN PRECISE LOCATION OF
FLOODING POTENTIAL...SO FOR NOW WILL HOLD OFF ON ANY FLASH FLOOD
WATCH.


.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 346 AM CDT TUE AUG 26 2014

WET PATTERN CONTINUES INTO MID AND LATE WEEK IS ASSOCIATION WITH A
VERY SLOWLY EVOLVING UPPER LEVEL PATTERN. WITH A PERSISTENT JET
STREAK POINTED AT OUR SOUTHERN FORECAST AREA...A STEADY STREAM OF
MOISTURE AND A STALLED MID LEVEL BOUNDARY PERSISTING OVER NORTHEAST
NEBRASKA AND NORTHWEST IOWA...A PROLONGED PERIOD OF WET WEATHER IS
IN STORE. A PARADE OF MID LEVEL WAVES WILL HELP SPARK SEVERAL ROUNDS
OF CONVECTION...MAINLY ACROSS OUR OUR SOUTHEASTERN HALF.

PRECIPITABLE WATER VALUES REMAIN SIGNIFICANTLY HIGH ACROSS OUR
SOUTHERN HALF...AND COULD REACH AS MUCH AS 2 INCHES BY WEDNESDAY IN
THE SIOUX CITY AREA...DECREASING TO THE NORTH. THE MAIN CONCERN WITH
ANY CONVECTION THROUGH THURSDAY WILL BE VERY HEAVY RAINFALL...WHICH
COULD VERY WELL TRAIN OVER AREAS FOR MULTIPLE DAYS. COULD SEE SOME
GROUND SATURATION ISSUES...PARTICULARLY THROUGH OUR EXTREME SOUTHERN
COUNTIES - NEAR THE HIGHWAY 20 CORRIDOR WHERE GREATEST LIFT AND
MOISTURE...AND PRECIPITATION PROBABILITY WILL RESIDE. WILL HAVE TO
CONTINUE TO MONITOR FOR FLASH FLOODING AND RIVER FLOODING ISSUES AS
THIS SYSTEM EVOLVES. RATHER SKINNY CAPE VALUES...TEMPERATURES COOLED
BY RAIN AND OVERCAST SKIES...AND OVERALL WEAK SHEAR WILL KEEP THE
SEVERE THREAT MINIMAL DURING THE PERIOD.

MODELS REMAIN CONSISTENT WITH PAINTING THIS WET PATTERN...HOWEVER WE
CONTINUE TO SEE SOME SLIGHT TIMING AND TRACK DISCREPANCIES OF THE
SHORTWAVES...BUT OVERALL THESE DIFFERENCES ARE MINOR. LATEST RUNS
ARE TRENDING THINGS A BIT FURTHER NORTHEAST...BRINGING BETTER
POTENTIAL FOR SOME LOCALLY HEAVY PRECIPITATION FURTHER INTO
SOUTHWEST MINNESOTA ON THURSDAY...MAINLY SEEN IN THE ECMWF AND
NAM...SO DID NUDGE LIKELY POPS INTO THIS AREA. IT DOES LOOK LIKE OUR
NORTHWEST CORNER - NEAR THE HIGHWAY 14 CORRIDOR IN SOUTH DAKOTA -
WILL STRUGGLE TO SEE MUCH OF ANY PRECIPITATION DURING THIS
PERIOD...BUT LEFT SOME LOW END POPS WEDNESDAY NIGHT AND THURSDAY FOR
COLLABORATION.

MODELS REMAIN SLOW TO KICK THE UPPER TROUGH FROM OUT OF THE PLAINS.
EXPECT MID LEVEL BOUNDARY TO WEAKEN LATER IN THE WEEK WHILE THE
FORCING GRADUALLY SAGS EAST OF OUR FORECAST AREA. RAIN CHANCES
PERSIST ACROSS OUR SOUTHEASTERN HALF THURSDAY NIGHT AND SLOWLY
SHIFTS EAST OF THE AREA THROUGH SATURDAY. WITH WANING SUPPORT DURING
THIS PERIOD...THE HEAVY RAIN THREAT WILL BE LARGELY OVER. DRY
WEATHER FINALLY TAKES HOLD THIS WEEKEND WITH A BRIEF RETURN OF UPPER
LEVEL RIDGING...BUT MODELS BEGIN TO DIVERGE AGAIN MOVING INTO EARLY
NEXT. TEMPERATURES WILL FINALLY RETURN TO NEAR NORMALS IN THE 80S
AFTER A PROLONGED PERIOD OF HIGHS IN THE 70S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1052 PM CDT MON AUG 25 2014

CONVECTIVE DEVELOPMENT CONTINUES TO BE GREATEST CHALLENGE IN THE
TAF PERIOD. MID LEVEL BOUNDARY NEAR KSUX WITH CLOUDS AND EVEN A FEW
LIGHT SHOWERS WILL PERSIST...WITH STRONGER FORCING FOR LIFT ARRIVING
INTO THE AREA TOWARD 10-12Z. KSUX LOOKS TO BE ON NORTHERN EDGE OF
ANY THREAT FOR CONVECTION LATE IN CURRENT NIGHT AND EARLY MORNING...
AND FOR NOW WITH ONLY MINIMAL ELEVATED CAPE AND BETTER FORCING
REMAINING SOUTH...HAVE KEPT PRECIP MENTION TO JUST SHOWERS. STRONGER
WAVE CROSSING FLAT RIDGE TOWARD EVENING...AND INCREASE IN MID LEVEL
THETA E ADVECTION AND SLIM ELEVATED INSTABILITY COULD RESULT IN
A FEW SHOWERS TOWARD KHON/KFSD BY LATE AFTERNOON. BEST FORCING
COMES IN AGAIN AFTER DARK...AND WILL FAVOR AREAS SOUTH OF INTERSTATE
90...INCLUDING THE KSUX TAF...FOR MENTION OF THUNDERSTORMS. HAVE KEPT
CONDITIONS VFR FOR THE TIME BEING...BUT ANY ORGANIZED THUNDERSTORM
ACTIVITY MAY CONTAIN A BRIEF DROP INTO MVFR BY TOMORROW EVENING.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...
LONG TERM...
AVIATION...CHAPMAN







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