Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 241004
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
504 AM CDT SUN AUG 24 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 503 AM CDT SUN AUG 24 2014

LOW LEVEL JET STRENGTHENING EARLY THIS MORNING AND NOSING INTO
NORTHEAST NEBRASKA HAS ALLOWED A SECONDARY COMPLEX OF THUNDERSTORMS
TO DEVELOP ALONG AN ENHANCED AREA OF 850 MB FRONTOGENESIS. STALLED
FRONTAL BOUNDARY HAS ALSO SET UP ACROSS OUR SOUTHERN CWA...FURTHER
SUPPORTING THE ONGOING ACTIVITY. WHILE THE CURRENT ACTIVITY IS
LIFTING RAPIDLY NORTHEASTWARD...WITH DEEP INSTABILITY...
FRONTOGENETIC LIFT AND SHEAR...SCATTERED THUNDERSTORMS WILL LIKELY
CONTINUE TO REDEVELOP IN THIS AREA THROUGH AROUND DAYBREAK. CANNOT
RULE OUT A STRAY MARGINAL SEVERE STORM WITH QUARTER SIZE HAIL AND
GUSTS AROUND 60 MPH...BUT THE MAIN IMPACT WITH THESE STORMS WILL BE
VERY HEAVY RAINFALL...GIVEN AMPLE MOISTURE AND PWAT VALUES NEAR 1.90.

EXPECT A BREAK OR GENERALLY DECREASE IN THE SHOWERS AND
THUNDERSTORMS AROUND MID MORNING...BUT WITH DAYTIME HEATING AND
CONTINUED INSTABILITY AND LIFT ALONG THE VERY SLOW MOVING
BOUNDARIES...ADDITIONAL SCATTERED SHOWER AND THUNDERSTORM ACTIVITY
WILL DEVELOP AGAIN AS A WEAK MID LEVEL WAVE TRACKS INTO THE REGION.
THESE STORMS WILL BE GENERALLY FROM NEAR THE INTERSTATE 29 CORRIDOR
INTO OUR EASTERN HALF OF THE FORECAST AREA...THEN GRADUALLY SHIFT
EASTWARD THROUGH THE LATE AFTERNOON AND EVENING. MODELS SUGGEST THAT
LAPSE RATES INCREASE WHILE CAPE VALUES WILL PEAK AROUND 1500 TO 2000
J/KG WITH BULK SHEAR AROUND 30 TO 35 KT IN OUR EAST. COULD SEE A FEW
ISOLATED SEVERE STORMS PULSE UP LATE AFTERNOON AND EVENING WITH
MARGINAL THREAT OF 60 MPH WINDS AND HAIL TO QUARTER SIZE...IN
ADDITION TO HEAVY DOWNPOURS. HIGHS TODAY WILL VARY FROM NEAR 80 IN
OUR FAR WEST TO NEAR 90 IN THE FAR SOUTHEAST.

LIGHT NORTHERLY WINDS ARRIVE TONIGHT BEHIND THE WASHED OUT BOUNDARY.
SKIES WILL CLEAR FROM WEST TO EAST...WITH LOWS WILL IN THE 50S TO
LOWER 60S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 503 AM CDT SUN AUG 24 2014

VERY ACTIVE WEATHER PATTERN SETTING UP IN THE EXTENDED...BUT WILL
HAVE ABBREVIATED DISCUSSION DUE TO ONGOING WEATHER. 00Z MODELS
CONTINUE TO SHOW ELEVATED BOUNDARY ACROSS SOUTHERN PORTIONS OF
FORECAST AREA STALLING MONDAY THROUGH THURSDAY WITH THE POTENTIAL
FOR TRAINING ECHOES AND LOCALLY HEAVY RAINFALL.  HAVE CONTINUED TO
INCREASE POPS AND QPF ESPECIALLY ACROSS SOUTHERN THIRD OF THE
FORECAST AREA...ESPECIALLY THROUGH THE OVERNIGHT PERIODS AS STRONG
LOW LEVEL JET FEEDS INTO ORTHOGONALLY ORIENTED BOUNDARY.  WILL
LIKELY NEED TO ISSUE FLASH FLOOD WATCH SOON FOR PORTIONS OF FORECAST
AREA...BUT DIDN/T HAVE TIME TO COORDINATE WITH ACTIVE WEATHER.
PRECIPITABLE WATER VALUES CLIMB THROUGHOUT THE WEEK WITH THE GULF
WIDE OPEN...APPROACHING TWO INCHES BY WEDNESDAY.  LIKE PREVIOUS
FORECASTER ALLUDED TO IN DISCUSSION YESTERDAY...COLD POOL WITH THE
INITIAL ROUND OF CONVECTION WILL LIKELY AUGMENT THE BOUNDARY
LOCATION...BUT MODEL SOLUTIONS CONTINUE TO POINT TOWARD HEAVY
RAINFALL EVENT THROUGH AROUND THURSDAY OF THIS WEEK. AS IS
TYPICAL...THE GFS IS FASTER IN PROGRESSING THE OVERALL
PATTERN...WHILE THE ECMWF AND CANADIAN SUGGEST A SLOWER EVOLUTION OF
THE PATTERN WITH PRECIPITATION THREAT LINGERING INTO LATE IN THE
WEAK.  WITH RELATIVELY WEAK FLOW IN THE MID LEVELS OF THE ATMOSPHERE
AND RELATIVELY QUIET WEATHER PATTERN...WOULD HEDGE TOWARDS WET
PATTERN LASTING THROUGH AT LEAST THURSDAY IF NOT FRIDAY BEFORE UPPER
WAVE MOVES THROUGH AND DRYING PERIOD CAN BEGIN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1159 PM CDT SAT AUG 23 2014

MVFR-IFR CEILINGS/VISIBILITY AS WELL AS AREAS OF CONVECTION WILL BE
PRIMARY AVIATION CONCERNS AS TAF PERIOD BEGINS. BOTH CONDITIONS ARE
EXPECTED TO EXIT THE FORECAST AREA TO THE NORTHEAST THROUGH THE
EARLY-MID MORNING HOURS...FOLLOWED BY VFR CONDITIONS THE REMAINDER
OF SUNDAY INTO SUNDAY NIGHT. ISOLATED CONVECTION AGAIN POSSIBLE IN
EASTERN PARTS OF THE AREA SUNDAY AFTERNOON AS COLD FRONT MOVES
EAST...BUT LOCATION/TIMING/COVERAGE DIFFICULT TO PINPOINT AT THIS
RANGE AND HAVE NOT INCLUDED MENTION IN TAFS AT THIS TIME.


&&

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

$$

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





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