Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 311110
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
610 AM CDT MON AUG 31 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CDT MON AUG 31 2015

WARM...HUMID AND SOMEWHAT BREEZY DAY IN STORE FOR THE REGION AHEAD
OF WEAK COOL FRONT...PROGGED TO PUSH INTO WESTERN PORTIONS OF THE
FORECAST AREA THIS AFTERNOON. CONTINUES TO LOOK LIKE THE FRONT WILL
ENTER THE AREA DRY AS LIMITED MOISTURE BELOW 10KFT ALLOWS STRONG CAP
TO REMAIN IN PLACE. EXPECT HIGHS TO RANGE FROM LOWER 80S NEAR/EAST
OF I-29...TO NEAR 90 WHERE MIXING IS MAXIMIZED IN THERMAL RIDGE JUST
AHEAD OF THE BOUNDARY.

FRONT STALLS NEAR LAKE ANDES TO KBKX/KMML LINE OVERNIGHT...WITH
HUMID AIR MASS HOLDING TEMPERATURES IN THE LOWER-MID 60S TONIGHT...
OR AROUND 10 DEGREES ABOVE NORMAL LOW TEMPERATURES FOR THE 1ST OF
SEPTEMBER. MOISTURE STILL SOMEWHAT LACKING BETWEEN THE ABUNDANT
SURFACE HUMIDITY AND MID LEVELS...BUT WITH WEAK DESTABILIZATION AS
MID LEVEL WAVE APPROACHES FROM THE SOUTHWEST...THINK WE COULD SEE A
FEW ACCAS SHRA/TSRA DEVELOP LATE TONIGHT AND HAVE ADDED A LOW POP TO
SOUTHWEST PORTIONS OF THE CWA AFTER 06Z.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 340 AM CDT MON AUG 31 2015

WITH UPPER LEVEL RIDGING DOMINATING ACROSS THE REGION...THE EXTENDED
PERIOD WILL BE CHARACTERIZED BY ABOVE NORMAL TEMPERATURES AND
PERIODIC LOW END RAIN CHANCES INTO FRIDAY. THIS WILL PLAY OUT TO
HIGHS GENERALLY MID 80S TO LOWER 90S AND LOWS IN THE UPPER 60S.

IN THE NEARER TERM...LEFT TUESDAY DRY AS THE BOUNDARY WASHES OUT
OVER OUR AREA. ON TUESDAY NIGHT THETA E ADVECTION AND INSTABILITY
INCREASES ACROSS THE AREA AS A SHORTWAVE LIFTS INTO THE REGION AND A
LOW LEVEL JET DEVELOPS AND FOCUSES THROUGH THE SOUTHEASTERN PORTIONS
OF THE CWA OVERNIGHT. RELATIVE TO THAT...KEPT SMALL THUNDERSTORM
CHANCES THROUGH OUR LOWER MO RIVER VALLEY AND NORTHWESTERN IOWA
ZONES DURING THAT TIME FRAME. LOOKS TO BE A REPEAT PERFORMANCE ON
WEDNESDAY NIGHT WITH THUNDERSTORM CHANCES OVER OUR SOUTHEASTERN
ZONES.

BETTER THUNDERSTORM CHANCES THEN COME INTO PLAY BY FRIDAY NIGHT AND
INTO NEXT WEEKEND AS AN UPPER LEVEL TROUGH OVER THE WESTERN CONUS
BEGINS TO NUDGE EASTWARD...AS SHORTWAVES EJECT OUT OF THE TROUGH AND
INTO OUR AREA. MODEL DIFFERENCES ALSO BEGIN TO GROW TOWARD THE END
OF THE EXTENDED...MOST NOTICEABLE WITH THE TIMING OF A FRONTAL
PASSAGE SOMETIME IN THE SATURDAY TO MONDAY TIME FRAME...WITH THE GFS
MUCH QUICKER THAN THE ECMWF. THIS WILL PUT AN END TO THE ABOVE
NORMAL TEMPERATURES AS MUCH COOLER AIR FILTERS IN BEHIND THE
SYSTEM...THOUGH CONFIDENCE LOW ON WHAT DAY THIS WILL ACTUALLY HAPPEN
WITH MODEL TIMING DIFFERENCES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 610 AM CDT MON AUG 31 2015

AREAS MVFR-IFR VISIBILITY IN FOG/STRATUS...WITH LOCALIZED LIFR
CONDITIONS...FOR CENTRAL AND EASTERN PORTIONS OF THE FORECAST AREA
EARLY THIS MORNING. EXPECT CONDITIONS TO IMPROVE TO VFR BY 14Z-15Z
AS 20-30KT LOW LEVEL JET BEGINS TO MIX THROUGH STABLE BOUNDARY
LAYER. WEAK FRONT WILL MOVE INTO FAR WESTERN FORECAST AREA THIS
AFTERNOON. AREAS EAST OF THE FRONT WILL SEE OCCASIONAL GUSTS OF
20-25KT TODAY...DIMINISHING EARLY THIS EVENING. FRONTAL BOUNDARY
WILL STALL ACROSS THE REGION TONIGHT...RESULTING IN VARIABLE WINDS
UNDER 10KTS. WITH LIGHT WINDS AND HUMID AIR MASS IN PLACE...COULD
SEE REDEVELOPMENT OF FOG LATE IN THE TAF PERIOD. HOWEVER FORECAST
SOUNDINGS SHOW NEAR SURFACE MOISTURE LAYER TO BE MORE SHALLOW THAN
THIS MORNING...SO COULD RESULT IN MORE OF A SHALLOW FOG EVENT...
THOUGH AGAIN AREAS NEAR/EAST OF I-29 WOULD BE MOST SUSCEPTIBLE.
WITH CONFIDENCE LOW...WILL KEEP VISIBILITY VFR TONIGHT...BUT LATER
SHIFTS WILL NEED TO EVALUATE FURTHER.

&&

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

$$

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


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