Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 271709
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1209 PM CDT WED AUG 27 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 442 AM CDT WED AUG 27 2014

ACTIVE FORECAST WITH A COUPLE DIFFERENT ROUNDS OF CONVECTION
EXPECTED ACROSS THE FORECAST AREA. 08Z RADAR AND SURFACE ANALYSIS
DEPICT SURFACE BOUNDARY HAS WANDERED SOUTH TOWARDS THE I-70
CORRIDOR.  SHORT WAVE MOVING ACROSS THE BOUNDARY HAS LEAD TO THE
DEVELOPMENT OF A TRAILING STRATIFORM MCS ACROSS SOUTH CENTRAL
NEBRASKA.  FURTHER TO THE NORTH...LEADING EDGE OF THE ELEVATED
MOISTURE RETURN HAS LEAD TO THE DEVELOPMENT OF A CONVECTIVE BAND
OVER THE LAST HOUR ACROSS NORTHERN NEBRASKA.  THIS MOISTURE IS
EXPECTED TO EXPAND NORTH AND EAST THROUGH THE MORNING HOURS IN
ADVANCE OF THE SHORT WAVE LIFTING FROM SOUTHWEST NEBRASKA.  HAVE
BOLSTERED POPS ACROSS THE SOUTHERN CWA THROUGH THE MORNING HOURS. IN
GENERAL...STORMS SHOULD BE RELATIVELY SLOW MOVERS WITH LIGHT FLOW IN
THE LOWEST 20K FEET OF THE ATMOSPHERE.  MOISTURE TRANSPORT INTO THE
REGION TODAY IS EXPECTED TO LEAD TO A STEADY CLIMB IN PWAT VALUES
THROUGHOUT THE DAY APPROACHING THE TWO INCH THRESHOLD BY LATE IN THE
AFTERNOON. AS SHORTWAVE APPROACHES FROM THE SOUTHWEST...EXPECT
CONVECTION TO REDEVELOP ACROSS NORTHEAST NEBRASKA AND LIFT NORTH
THROUGH THE EVENING INTO THE OVERNIGHT HOURS.  MODELS ARE
CONVECTIVELY POLLUTED BY TONIGHT...SO HARD TO PICK UP ON ANY
ELEVATED BOUNDARIES THAT MAY RESULT IN TRAINING OF ECHOS...BUT AM
MOST CONCERNED ABOUT THE POTENTIAL FOR FLASH FLOODING IN SOUTHERN
TIER OF FORECAST AREA FROM DIXON TO IDA COUNTIES WHERE RAINFALL OVER
THE LAST WEEK HAS ACCUMULATED TO 2-4 INCHES AND ADDITIONAL RAINFALL
IS EXPECTED THIS MORNING. WITH MODEL UNCERTAINTY ON WHERE HEAVIEST
PRECIPITATION WILL FALL...OPTED TO HOLD OFF ON ISSUING A FLASH FLOOD
WATCH FOR NOW.  NAM OFFERS THE FURTHEST NORTH AND MOST PROGRESSIVE
SOLUTION...WHILE THE GFS...CANADIAN AND ECMWF FOCUS FURTHER SOUTH
ACROSS NORTHWEST IOWA.  SIDED CLOSER TO THESE SOLUTIONS...BUT HEDGED
TOWARDS THE SLOWER EVOLVING SOLUTIONS SINCE THIS PATTERN HAS BEEN
SLOWER THAN ANTICIPATED.

HAVE RAISED QPF VALUES FOR TODAY INTO TONIGHT WITH 1-2 INCHES
FORECAST ACROSS NORTHWEST IOWA...BUT CERTAINLY POTENTIAL EXISTS FOR
HIGHER AMOUNTS.  IN TERMS OF TEMPERATURES...HAVE SHRUNK THE DIURNAL
FLUCTUATION BY RAISING LOWS TONIGHT WITH PLENTY OF CLOUDS AND
CONVECTION AROUND.


.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 442 AM CDT WED AUG 27 2014

WET PATTERN CONTINUES THROUGH THE END OF THE WEEK IN ASSOCIATION
WITH THE VERY SLOWLY EVOLVING UPPER LEVEL PATTERN.

RAIN CHANCES WILL LARGELY BE FOCUSED ACROSS OUR SOUTHEASTERN HALF AS
THE UPPER TROUGH FINALLY DRIFTS EASTWARD ACROSS THE CENTRAL PLAINS
THURSDAY AND FRIDAY BEFORE GRADUALLY LIFTING NORTHEAST INTO
WISCONSIN FRIDAY NIGHT AND SATURDAY.

FOR THURSDAY...MODELS STILL SHOWING SOME PRETTY SIGNIFICANT
DIFFERENCES IN THE TRACK OF A SHORTWAVE MAINLY IMPACTING THE AREA IN
THE MORNING. THE NAM AND NMM PLACE THIS WAVE MUCH FURTHER NORTH NEAR
THE HIGHWAY 14 CORRIDOR...WHICH IS A STRONG OUTLIER FROM THE OTHER
MODELS WHICH ARE MORE CONSISTENT WITH PREVIOUS MODEL RUNS BY
BRINGING THE WAVE THROUGH NORTHWEST IOWA. HAVE THROWN OUT THIS
SOLUTION...SO EXPECT THE SLOW MOVING SHOWERS AND THUNDERSTORMS WITH
SOME PRETTY HEFTY RAINFALL RATES TO MAINLY IMPACT OUR FAR EASTERN
CWA. AS THIS WAVE PULLS AWAY FROM THE REGION IN THE
AFTERNOON...PRECIPITATION CHANCES TAPER OFF FROM THE NORTHWEST
THURSDAY AFTERNOON AND NIGHT.

CONTINUED MOISTURE PRESENCE AND INSTABILITY COINCIDENT WITH THE
GRADUAL ARRIVE OF THE UPPER TROUGH ACROSS OUR SOUTHEASTERN
HALF...SCATTERED SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE IN
THIS AREA FRIDAY INTO SATURDAY...SLOWLY DRYING FROM THE WEST EACH
PERIOD. MOISTURE WILL BE MORE LIMITED...SO HEAVY RAINFALL CHANCES
DWINDLE SOMEWHAT...BUT THERE COULD POTENTIALLY BE SOME RESIDUAL
CONCERN OF ADDITIONAL RAINFALL IN ALREADY SATURATED SOILS AND SOME
ADDITIONAL RIVER AND STREAM RISES.

A BRIEF RETURN OF UPPER LEVEL RIDGING AND TEMPERATURES FINALLY
RETURNING TO NEAR OR EVEN ABOVE NORMALS ARRIVES SATURDAY AFTERNOON
AND SUNDAY. MODELS POTENTIALLY BRING A FRONT THROUGH THE NORTHERN
PLAINS ON SATURDAY NIGHT OR SUNDAY...WITH A MORE SUBSTANTIAL
SHORTWAVE BRINGING A BETTER CHANCE OF ADDITIONAL WET WEATHER SUNDAY
NIGHT. BUT WITH QUICKLY DIVERGING MODEL SOLUTIONS EARLY NEXT
WEEK...CONFIDENCE IS FAIRLY LOW. DID NOT ALTER ALLBLEND SOLUTION
MUCH GIVEN THE UNCERTAINTY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1205 PM CDT WED AUG 27 2014

SHOWERS AND LOW CEILINGS WILL PERSIST ALONG THE LOWER MISSOURI
RIVER VALLEY THROUGH THE AFTERNOON...OTHERWISE EXPECT SHOWERS AND
THUNDERSTORMS TO DEVELOP THROUGH NEBRASKA THIS EVENING THEN EXPAND
NORTHWARD TONIGHT. WILL BE REDUCED VISIBILITIES IN HEAVIER
ACTIVITY OVERNIGHT...WITH IMPROVEMENT AFTER 12Z ON THURSDAY.

&&

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

$$

SHORT TERM...
LONG TERM...
AVIATION...JM





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