Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 250501
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1159 PM CDT SUN AUG 24 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 424 PM CDT SUN AUG 24 2014

FRONT HAS PUSHED THROUGH MOST OF THE CWA THIS AFTERNOON...CURRENTLY
RESIDING FROM JUST EAST OF WORTHINGTON SOUTHWARD AND EAST OF ORANGE
CITY TO OMAHA. A FEW WIDELY SCATTERED STORMS MAY PERSIST AHEAD OF
THIS BOUNDARY...BUT WILL QUICKLY MOVE SOUTHEAST THIS EVENING.  DEW
POINTS HAVE FALLEN INTO THE 50S THIS AFTERNOON WEST OF INTERSTATE
29...WHICH SHOULD ALLOW FOR COOL TEMPERATURES OVERNIGHT.  LOWS WILL
BOTTOM OUT IN THE LOWER 50S TO LOWER 60S IN THE FAR EAST.

THE DAYTIME HOURS OF MONDAY WILL CONTINUE TO FAVOR DRY CONDITIONS AS
HIGH PRESSURE DROPPING SOUTH INTO THE DAKOTAS WILL KEEP QUALITY
MOISTURE LOW. BY THE AFTERNOON...SHORTWAVE ENERGY WILL BEGIN TO
EJECT EASTWARD FROM THE CENTRAL ROCKIES AS RIGHT ENTRANCE REGION OF
DEPARTING UPPER JET MOVES OVERHEAD.   A SLIGHT INCREASE IN MID AND
UPPER CLOUD COVER IS THE MOST LIKELY RESULT...WITH AN OUTSIDE CHANCE
FOR A SPRINKLE SOUTH OF THE MISSOURI RIVER LATE IN THE AFTERNOON.


.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 424 PM CDT SUN AUG 24 2014

THE MAIN CONCERN FOR THE WEEK IS THE REPEATED CHANCES OF HEAVY
RAINFALL BEGINNING ON MONDAY NIGHT AND CONTINUING INTO AT LEAST
THURSDAY.

THE ENTRANCE REGION OF A 65 KT 300 MB JET WILL SET UP ACROSS THE
EASTERN DAKOTAS ON MONDAY NIGHT. THIS WILL PUT THE MISSOURI VALLEY
AND NRN IOWA IN THE RIGHT ENTRANCE REGION OF THE JET. AT THE SAME
TIME A STRONG 850 MB THETA-E GRADIENT WILL SET UP FROM THE
NEBRASKA AND SOUTH DAKOTA BORDER INTO NRN IA. FINALLY...A 30 TO 40
KT LOW LEVEL JET WILL DEVELOP IN THE EVENING WITH STRONG MOISTURE
TRANSPORT INTO THE FRONTAL ZONE. WITH MODERATE INSTABILITY SOUTH
OF THE BOUNDARY...EXPECT THUNDERSTORMS TO DEVELOP DURING THE LATE
AFTERNOON AND EARLY EVENING IN THE VICINITY OF HIGHWAY 20...MOST
LIKELY IN NORTHEAST NEBRASKA. AS THE NIGHT PROGRESSES EXPECT
THUNDERSTORMS TO BECOME ORGANIZE AND GROW UPSCALE AS THEY MOVE
EAST OR EAST NORTHEAST. EXPECT THAT THE HEAVIEST RAINFALL WILL BE
ALONG OR SOUTH OF HIGHWAY 20...WHERE AROUND AN INCH IS LIKELY AND
LOCAL AMOUNTS REACHING OR EVEN EXCEEDING 2 INCHES IS POSSIBLE.
ALSO...WITH STORM MOTION PRIMARILY EAST OR EAST-NORTHEAST...ANY
RAINFALL WILL STRUGGLE TO GET MUCH NORTH OF HIGHWAY 18. THEREFORE
HAVE LOWERED POPS AND RAINFALL AMOUNTS ALONG I90...WITH DRY
WEATHER EXPECTED ALONG HIGHWAY 14 IN BOTH SD AND MN. WITH DRIER
AIR ASSOCIATED WITH HIGH PRESSURE OVER THE EASTERN DAKOTAS...LOWS
WILL RANGE FROM 50 TO 55 ALONG AND NORTH OF I90 WITH MID TO UPPER
50S SOUTH.

CONVECTION FROM MONDAY NIGHT WILL MOVE EAST AND GRADUALLY
DISSIPATE ON TUESDAY MORNING. THERE WILL LIKELY BE AT LEAST A
BRIEF BREAK IN THE CONVECTION LATE TUESDAY MORNING AND EARLY
AFTERNOON. BUT WITH THE JET STREAK EXTENDING FROM THE EASTERN
DAKOTAS INTO THE GREAT LAKES AND THE BOUNDARY REMAINING IN PLACE
AS WELL AS DESTABILIZATION IN THE WARM SECTOR...ADDITIONAL
CONVECTION COULD DEVELOP. THIS WILL MOST LIKELY BE OVER EASTERN
NEBRASKA BUT A FEW STORMS MAY DEVELOP OR MOVE AS FAR NORTH AS
HIGHWAY 20 ESPECIALLY DURING THE LATE AFTERNOON. DRY WEATHER IS
EXPECTED TO CONTINUE NORTH OF I90 WITH ONLY A SMALL CHANCE FOR A
SHOWER OR THUNDERSTORM SOUTH OF HIGHWAY 14. WITH AMPLE CLOUDS AND
A COOL NORTHEAST WIND...HIGHS WILL BE IN THE UPPER 60S TO LOWER
70S.

ANOTHER ROUND OF CONVECTION IS EXPECTED ON TUESDAY NIGHT AS A WEAK
UPPER WAVE MOVE EASTWARD OVER THE 850 MB BOUNDARY. THIS AREA OF
RAIN LOOKS TO BE IN THE SAME AREA OR PERHAPS A BIT SOUTH OF WHERE
RAIN OCCURS ON MONDAY NIGHT. THE EXACT LOCATION WILL BE DEPENDENT
UPON HOW MUCH THE COLD POOL FROM MONDAY NIGHT/S CONVECTION ADVECTS
THE FRONT SOUTH. BECAUSE OF THE INCREASED UNCERTAINTY IN
AREA...HAVE A BROADER GRADIENT IN POPS NORTH OF THE BOUNDARY WHICH
RESULTS IN A 50 PERCENT CHANCE UP TO I90 AND A SLIGHT CHANCE ALONG
HIGHWAY 14. HOWEVER...THE HEAVIEST RAINFALL LOOKS TO BE AGAIN
CLOSE TO OR SOUTH OF HIGHWAY 20 IN NEBRASKA AND IOWA WHERE ANOTHER
1 TO 2 INCHES OF RAIN IS POSSIBLE. THUNDERSTORMS SHOULD AGAIN
SLOWLY DISSIPATE ON WEDNESDAY MORNING AS THEY MOVE TO THE EAST
NORTHEAST.

THE JET STREAK WILL BEGIN TO LIFT NORTHEAST ON WEDNESDAY AS A VERY
SLOW MOVING WAVE BEGINS TO MOVE OUT OF THE ROCKIES AND INTO THE
HIGH PLAINS. THIS IS EXPECTED TO ALLOW THE BOUNDARY TO SLOWLY LIFT
NORTHWARD. HOW FAST IS REALLY DEPENDENT UPON HOW STRONG THE COLD
POOL IS FROM TUESDAY/NIGHT CONVECTION. BUT IT SHOULD BE FAR ENOUGH
NORTH THAT THUNDERSTORMS WILL BEGIN TO REDEVELOP BY LATE AFTERNOON
FROM THE NEBRASKA AND SOUTH DAKOTA BORDER EASTWARD INTO NORTHWEST
IOWA. AS WITH THE PREVIOUS TWO NIGHTS...THESE STORMS SHOULD GROW
UPSCALE AND SPREAD EAST OR EAST NORTHEAST ON WEDNESDAY NIGHT. THE
HEAVIEST RAIN THIS NIGHT LOOKS TO EXTEND FARTHER NORTH...PERHAPS UP
TO I90 BY THURSDAY MORNING IN SW MN. WITH THE INCREASED
UNCERTAINTY...KEPT POPS FROM 60 TO 70 PERCENT IN NW IA AND ALSO
EXTENDED THE CHANCE FOR THUNDERSTORMS UP TO HIGHWAY 14.

MODEL SOLUTIONS BEGIN TO DIVERGE BY WEDNESDAY NIGHT WITH THE GFS
MUCH FASTER THAN THE ECMWF...NAM...OR GEM. THE GEM IS ALSO FARTHER
NORTH THAN THE OTHER TWO LONGER RANGE MODELS...SO GENERALLY SIDED
CLOSER TO THE ECMWF. THE ECMWF ITSELF BRINGS THE POTENTIAL FOR
MORE RAIN THROUGH FRIDAY NIGHT. THAT IS SLOWER THAN EVEN THE GEM.
SO INCREASED POPS THURSDAY AND THURSDAY NIGHT TO CHANCE BASICALLY
EAST OF I29 AND EVEN HAVE A SLIGHT CHANCE OVER MOST AREAS EAST OF
I29 ON FRIDAY. AND WITH SUCH A STRONG WAVE AND SO MUCH MOISTURE
AVAILABLE...WILL NEED TO EXAMINE IF THERE COULD BE ANOTHER BOUT OF
HEAVY RAIN IN NORTHWEST IOWA LATE THURSDAY AND THURSDAY NIGHT.

NOT INCLUDING THURSDAY NIGHT...WE ARE LOOKING AT THE POTENTIAL OF
2 TO 4 INCHES OF RAIN...WITH LOCALLY HIGHER AMOUNTS...SOUTH OF A
LINE FROM SPENCER IOWA TO YANKTON SOUTH DAKOTA WITH THE HEAVIEST
RAIN ALONG OR SOUTH OF HIGHWAY 20. THE LIKELIHOOD OF HEAVY RAIN IS
INCREASING ALTHOUGH THE EXACT LOCATION OF THE HEAVIEST RAINFALL IS
STILL UNCERTAIN. THIS HEAVY RAIN MAY NOT ONLY RESULT IN A RISK OF
FLASH FLOODING BUT RISES ON LARGER RIVERS AND STREAMS. PERSONS
SOUTH OF I90...ESPECIALLY AROUND SIOUX CITY AND STORM
LAKE...SHOULD STAY ABREAST OF THE LATEST FORECASTS.

AFTER FRIDAY NIGHT...QUIETER WEATHER WILL MOVE INTO THE AREA WITH
WARMER TEMPERATURES BY NEXT WEEKEND.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1159 PM CDT SUN AUG 24 2014

VFR CONDITIONS WILL DOMINATE THROUGH THE DAY MONDAY...WITH WEST TO
NORTHWEST WINDS BELOW 15KT. CHANCE OF AFTERNOON CONVECTION RETURNS
TO SOUTHERN PARTS OF THE FORECAST AREA LATE IN THE AFTERNOON...WITH
CHANCES INCREASING AFTER 26/00Z. MVFR OR LOWER VISIBILITY POSSIBLE
WITH ANY TSRA THAT DEVELOP...MOST LIKELY TO AFFECT KSUX DURING THE
EVENING HOURS MONDAY THAN TAFS FARTHER TO THE NORTH.

&&

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

$$

SHORT TERM...DUX
LONG TERM...SCHUMACHER
AVIATION...JH







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