Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 121145
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
645 AM CDT SAT JUL 12 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 422 AM CDT SAT JUL 12 2014

PRIMARY SHORT TERM FOCUS HAS BEEN IN OUR FAR SOUTHERN ZONES AROUND
THE SIOUX CITY VICINITY WITH HEAVY RAIN. FORTUNATELY...ECHOES AND
RAIN RATES ARE NOW BEGINNING TO DECREASE. THIS IS ALSO TRUE UPSTREAM
IN NORTHEAST NEB WHERE MORE ECHOES IN THE 30-40DBZ CATEGORY ARE NOW
PREVALENT AS OPPOSED TO HIGHER ECHOES EARLIER. WILL CONTINUE TO
MONITOR FOR FLASH FLOODING POTENTIAL THROUGH THE EARLY MORNING HOURS
AS RAINFALL HAS BEEN OVER TWO INCHES AT THE KSUX AIRPORT THE PAST
SEVERAL HOURS. LEGACY RADAR ESTIMATION OF THE RAINFALL HAS BEEN VERY
GOOD...AND IS SHOWING A HEAVIER 3 INCHES AND MORE JUST SOUTH OF
SIOUX CITY. THE WIDESPREAD CONVECTION OVER OUR SOUTHERN ZONES HAS
BEEN ALONG A STATIONARY FRONTAL BOUNDARY AT THE SURFACE...WITH
CORFIDI VECTORS SHOWING NEARLY A STRAIGHT WEST TO EAST MOVEMENT. AS
EXPECTED THAT RAINFALL IS NOW BEGINNING TO NUDGE NORTHWARD TOWARD I
90...AND THIS TREND WILL CONTINUE THROUGH THE PRE DAWN AND EARLY
MORNING HOURS BUT WITH MUCH LESS RAINFALL EXPECTED. TO THE
WEST...VARIOUS HIRES MODELS HAVE DONE AN EXCELLENT JOB IN
FORECASTING DEVELOPING CONVECTION IN EAST CENTRAL SD. THIS ACTIVITY
IS ALONG ADVANCING VORTICITY IN THE MID LEVELS BUT MORE
IMPORTANTLY...WELL PLACED IN A 900-850MB CONVERGENCE ZONE JUST NORTH
OF AN ELEVATED FRONTAL BOUNDARY. TO THE NORTH OF OUR FORECAST
AREA...DRY AIR IS ENTRAINING SOUTHWARD...SO DOUBT THAT THE EAST
CENTRAL SD ACTIVITY WILL LAST MUCH PAST THE EARLY TO MID MORNING
HOURS. HOWEVER IT WILL LIKELY EXPAND EASTWARD INTO THE NORTHERN
SECTIONS OF SOUTHWEST MN AS THE EARLY MORNING PROGRESSES WITH
CORFIDI VECTORS SHOWING A WSW/ENE PROPAGATION OF THIS ACTIVITY. BUT
AGAIN...IT MAY REALLY STRUGGLE TO GO MUCH FURTHER NORTHWARD DUE TO A
LOT OF LOW LEVEL DRY AIR IN NORTHEAST SD.

AS SATURDAY PROGRESSES...THE AFOREMENTIONED MID LEVEL SHORT WAVE AND
VORTICITY MOVES EASTWARD ACROSS OUR AREA DURING THE MORNING...
REPLACED BY A STRONG WEST TO NORTHWEST FLOW ALOFT DURING THE
AFTERNOON. A STRONG JET WILL LIKELY HELP TO REFIRE OFF SOME SHOWERS
IN OUR NORTHERN ZONES THIS AFTERNOON...THEREFORE POPS WERE BEEFED UP
IN THAT AREA TO A HIGH END SCATTERED CATEGORY. FURTHER SOUTH...THERE
WILL LIKELY BE A STRIPE OF SHOWERS AND ISOLATED STORMS RIGHT ALONG
THE 900-850MB BOUNDARY CENTERED ALONG AN AXIS FROM SOUTHEAST SD...
TO EXTREME NORTHWEST IA AND THE SOUTHERN PORTION OF SOUTHWEST MN
LINGERING IN THE LATE MORNING AND EARLY AFTERNOON HOURS. THE
DIRECTIONAL CONVERGENCE ABOVE THE SURFACE WITH THIS BOUNDARY IS
QUITE STRONG...BUT THE WIND SPEEDS AND INSTABILITY ARE RATHER WEAK.
THEREFORE BELIEVE THAT RAINFALL RATES WILL NOT BE REAL EXCESSIVE AND
IN FACT...ONLY INCLUDED ISOLATED THUNDER WITH THE SHOWERS IN THE
LATE MORNING THROUGH AFTERNOON HOURS. SOME OF THE AFTERNOON ACTIVITY
WILL ALSO BE DIURNALLY HEATING DRIVEN THROUGHOUT THE ENTIRE FORECAST
AREA...WITH A RAPID DROP OFF IN CONVECTIVE ACTIVITY APPROACHING
SUNSET THIS EVENING. CURRENTLY THINK THAT OUR FORECAST AREA WILL BE
ENTIRELY PRECIPITATION FREE AFTER MIDNIGHT TONIGHT.

CLOUDS AND MOISTURE WILL HOLD DOWN TEMPERATURES TODAY...WITH A
SEASONABLY MILD NIGHT TONIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 422 AM CDT SAT JUL 12 2014

FRONTAL BOUNDARY WILL PUSH SOUTH ACROSS THE AREA ON SUNDAY. THIS
WILL BE THE FRONT THAT HELPS CLEAR OUT THE HIGHER DEWPOINTS...WITH
60S AHEAD OF THE FRONT...AND 40S AND 50S BEHIND IT. WITH COOLING
TEMPERATURES ALOFT...AND THE LINGERING LOW LEVEL MOISTURE AHEAD
OF THE FRONT...LOOKS LIKE WE SHOULD BE ABLE TO GENERATE AROUND 1000
J/KG OF CAPE BY LATE MORNING INTO THE AFTERNOON HOURS. GIVEN THE
TIMING OF THE FRONT...EXPECT THIS INSTABILITY TO BE FOCUSED SOUTH OF
INTERSTATE 90. CONVERGENCE ALONG THE BOUNDARY AND SOME WEAK PV
ADVECTION ROUNDING THE BASE OF THE TROUGH...MAY BE ENOUGH TO SPARK
OFF A FEW THUNDERSTORMS DURING THE AFTERNOON ALONG THE FRONT. STILL
SOME DISCREPANCIES ON TIMING OF THE FRONT AND STORM THREAT MAY VERY
WELL END UP SOUTH OF THE CWA...BUT WILL CONTINUE CHANCE POPS
SOUTHEAST OF A VERMILLION TO SPENCER IOWA LINE. DEEP LAYER SHEAR
WILL BE AROUND 40 KTS...HOWEVER GIVEN THE THIN WEAK CAPE AND DRY AIR
ALOFT...NOT SURE WE WILL BE ABLE TO FULLY TAKE ADVANTAGE OF THIS
SHEAR. CAN NOT RULE OUT A STRONGER STORM THOUGH IF CAPE ENDS UP A
BIT HIGHER...SO SOMETHING TO KEEP AN EYE ON. HIGHS WILL GENERALLY BE
IN THE MID AND UPPER 70S OVER SOUTHWEST MINNESOTA TO THE LOW AND MID
80S ELSEWHERE.

COOLER AIR BEGINS TO FILTER INTO THE REGION SUNDAY NIGHT INTO EARLY
NEXT WEEK AS A CUTOFF UPPER LOW ORIGINATING FROM NORTHERN CANADA
DROPS SOUTH INTO THE GREAT LAKES REGION. BREEZY NORTHWESTERLY WINDS
EXPECTED IN THE COLD AIR ADVECTION ON MONDAY...WITH GUSTS AROUND 30
MPH LIKELY. LOW TEMPERATURES MONDAY MORNING WILL BE IN THE
50S...WITH UPPER 40S TO LOW 50S COMMON TUESDAY MORNING AND WEDNESDAY
MORNING. TUESDAY MORNING WILL FEATURE THE COOLEST TEMPERATURES
ALOFT...BUT JUST ENOUGH OF A NORTHWESTERLY BREEZY SHOULD LINGER TO
PREVENT MOST OF US FROM REACHING OUR RECORD LOWS OF MID 40S. HIGH
TEMPERATURES MONDAY AND TUESDAY WILL BE 10 TO 20 DEGREES BELOW
NORMAL WITH MID 60S TO LOW 70S ON MONDAY AND UPPER 60S TO MID 70S ON
TUESDAY. RIDGING WILL BEGIN TO BUILD BACK INTO THE AREA WEDNESDAY
INTO FRIDAY AS THE TROUGH PUSHES OFF TO THE EAST. WILL THUS HAVE A
GRADUAL WARMING TREND EACH DAY...ALTHOUGH WILL LIKELY TAKE AT LEAST
UNTIL FRIDAY BEFORE TEMPERATURES APPROACH NORMAL LEVELS IN THE 80S.

PRECIPITATION CHANCES NEXT WEEK LOOK PRETTY MINIMAL WITH SURFACE HIGH
PRESSURE IN CONTROL. WILL LIKELY STAY MOSTLY SUNNY THOUGH THE
PERIOD...ALTHOUGH SOME DIURNALLY DRIVEN CU SEEM LIKELY GIVEN THE
COOL TEMPERATURES ALOFT...AT LEAST THROUGH THURSDAY. WITH THE TROUGH
AXIS PUSHING ACROSS ON MONDAY MORNING AND STEEP LOW LEVEL LAPSE
RATES...MAY BE ABLE TO GET A FEW ISOLATED SHOWERS INTO EARLY
AFTERNOON...MAINLY ACROSS SOUTHWEST MINNESOTA. EXPECT THESE TO WIND
DOWN BY MID AFTERNOON AS SUBSIDENCE AND DRYING TAKES OVER ON THE
BACKSIDE OF THE TROUGH. OTHER THAN THIS...IT LOOKS DRY THROUGH
FRIDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 645 AM CDT SAT JUL 12 2014

AVIATION CONDITIONS WILL BE QUITE TRICKY FOR TODAY. OCCASIONAL
SHOWERS AND THUNDERSTORMS WILL SLOWLY DRIFT SOUTHWARD THROUGH THE
DAY TODAY. THIS IS ON THE HEELS OF WIDESPREAD RAINFALL WHICH HAS
ALREADY FALLEN IN NORTHEAST NEBRASKA AND PARTS OF NORTHWEST IOWA.
BUT CURRENTLY...A BAND OF THUNDERSTORMS HAS DEVELOPED IN EAST
CENTRAL SD...AND INDICATIONS ARE IS THAT THIS BAND WILL EITHER
OOZE SOUTHWARD TOWARD I 90 IN THE LATE MORNING AND EARLY AFTERNOON...
OR NEW CONVECTION WILL DEVELOP ON ITS SOUTHWARD PROGRESSING OUTFLOW
BOUNDARY. THIS STANDS TO REASON...AS A DEFORMATION ZONE OF FLOW
JUST ABOVE THE SURFACE EXISTS ALONG I 90 DURING THE MIDDAY HOURS...
THEN MOVES SOUTHWARD INTO OUR SOUTHERN ZONES THIS AFTERNOON...IN
WHICH CASE MORE SHOWERS AND STORMS COULD THEN REDEVELOP IN
NORTHWEST IA IN THE MID AND LATE AFTERNOON HOURS. THE TAFS REFLECT
THIS SCENARIO...WITH DRYING CONDITIONS FINALLY TONIGHT. IN SHOWERS
AND STORMS...WOULD NOT BE SURPRISED AT ALL TO SEE IFR TO MVFR
CONDITIONS...WITH MVFR TO VFR PREVAILING OUTSIDE OF RAINFALL. LATE
TONIGHT IS ALSO A QUESTION MARK...IN THAT THERE COULD BE SOME FOG
POTENTIAL NOTING THE LIGHT WINDS AND MOIST GROUND. DID NOT INCLUDE
THIS YET AT KHON...AS MID LEVEL CLOUDS COULD MOVE INTO THAT AREA
LATE TONIGHT ALONG WITH A DRIER NORTHERLY FLOW OF SURFACE AIR...
FACTORS WHICH COULD HELP TO ABATE THE FOG AT KHON. PUT IN ONLY
MVFR FOG FOR NOW AT KFSD AND KSUX WHERE MID CLOUDS SHOULD BE
ABSENT. IF FOG DOES DEVELOP...IT COULD BE MUCH WORSE THAN MVFR...
SOMETHING TO WATCH AND PLAN FOR.

&&

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

$$

SHORT TERM...MJ
LONG TERM...CHENARD
AVIATION...MJ





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