Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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591
FXUS63 KFSD 152115
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
415 PM CDT FRI MAY 15 2015

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 414 PM CDT FRI MAY 15 2015

DEEP UPPER TROUGHING OVER THE SOUTHWESTERN UNITED STATES CONTINUES
TO POUR MOISTURE NORTHWARD INTO THE PLAINS THIS AFTERNOON.
HOWEVER...FOCUS FOR CONVECTION HAS BEEN SPLIT THROUGH MUCH OF THE
DAY...WITH MCV LIFTING NORTHWARD THROUGH WESTERN SD AND A SECONDARY
SHORTWAVE DRIVING CONVECTION IN THE MID/LOWER MISSOURI RIVER VALLEY.
 OVERHEAD...WEAK ISENTROPIC ASSENT TIED NEAR THE 305K SFC CONTINUES
TO PRODUCE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS.

HEADING INTO THE LATE AFTERNOON AND EVENING HOURS...MAIN FOCUS TURNS
TO WESTERN NE/SD AS UPPER JET BEGINS TO NOSE INTO THE PLAINS.
ALREADY A WELL DEVELOPED WARM FRONT STRETCHING ACROSS PORTIONS OF
NEBRASKA...BUT THE REINFORCING ELEVATED CONVECTION HAS KEPT THIS
BOUNDARY SW OF THE CWA THROUGH THE DAY.  WITH 850:700 MB FLOW
BEGINNING TO BACK INTO THE WESTERN PLAINS ONGOING SHOWER ACTIVITY IN
THE LOCAL AREA MAY BEGIN TO WANE AS EVENING APPROACHES WITH
CONVECTION OVER NEBRASKA PANHANDLE TAKING OFF.  WITH THE SFC WARM
FRONT TRYING TO REACH THE NE/SD LINE IN SOUTH CENTRAL SD...AN
ISOLATED STORM MAY STILL BE POSSIBLE EARLY THIS EVENING NEAR THE
MISSOURI RIVER.

THROUGH THE OVERNIGHT HOURS...LATEST HIGH RES GUIDANCE HINTS AT
SEVERAL CLUSTERS OF STORMS LIFTING NORTHEAST ACROSS NE/SD OVERNIGHT.
AS THE LEAD SHORTWAVE ENTERS THE PLAINS LATE THIS EVENING...WE MAY
BEGIN TO SEE THE LLJ VEER SOUTHWESTERLY WHICH COULD REIGNITE
ADDITIONAL ELEVATED CONVECTION FURTHER SOUTHEAST THROUGH CENTRAL
NEBRASKA AND SOUTH CENTRAL SD ALONG ELEVATED BOUNDARY LIFTING
NORTHEAST.   INSTABILITY WOULD BE WANING AT THIS POINT...BUT COULD
BE DEALING WITH MARGINAL HAIL OR PERHAPS BRIEF WIND GUSTS GIVEN
PARALLEL ORIENTATION OF LOW LVL FLOW. THIS STRONGER STORM RISK WOULD
MAINLY BE WEST OF THE JAMES RIVER INTO THE EARLY MORNING
HOURS...HOWEVER THE RISK OF CONVECTION COULD SPREAD ALL THE WAY
EASTWARD INTO WESTERN MN.

FOR SATURDAY...A VERY TRICKY FORECAST REMAINS.  DEEP MERIDIONAL FLOW
IS EXPECTED TO FURTHER ENHANCE MOISTURE OVERNIGHT INTO THE
AREA...WITH LLJ KEEPING ELEVATED CONVECTION LINGERING OVER THE CWA
INTO EARLY SATURDAY MORNING. A MUCH STRONGER WAVE WILL PIVOT INTO
THE PLAINS SATURDAY AFTERNOON. THE BIGGEST QUESTION FOR
SATURDAY...GIVEN THE DEEP MERIDIONAL FLOW...IS THE DEGREE OF CLOUD
COVER AND INSTABILITY THAT CAN GROW THROUGH THE AFTERNOON.  THERE
ARE SOME HINTS THAT LINGERING CLOUD COVER AND ELEVATED SHOWERS MAY
WORK TO REINFORCE THE EML IN THE AFTERNOON...WITH MODELS HINTING AT
A WEAK SHORTWAVE RACING NORTHWARD AND THROUGH THE AREA BY MID-DAY
SATURDAY.  HOWEVER...THE BEST CHANCE FOR ANY MORE SUBSTANCIAL GROWTH
IN SFC BASED INSTABILITY WILL BE ALONG A NORTH-SOUTH ORIENTATED SFC
BOUNDARY ACROSS WEST CENTRAL SD/NE.  THAT SAID...CANNOT RULE OUT A
FEW STRONG STORM CLUSTERS...MAINLY BOWING SEGMENTS FURTHER
EAST...ESPECIALLY IF STRONGER POCKETS OF INSTABILITY CAN GROW GIVEN
THE UNIDIRECTIONAL FLOW AND DECENT SPEED SHEAR ALOFT. AGAIN...VERY
CONDITIONAL AND UNCERTAIN.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 414 PM CDT FRI MAY 15 2015

THE CHANCE FOR THUNDERSTORMS WILL INCREASE RAPIDLY SATURDAY
EVENING AS A STRONG SHORT WAVE TROUGH AND JET STREAK MOVE
NORTHWARD INTO SOUTH DAKOTA. EXPECTED SCENARIO AT THIS TIME IS
THAT THUNDERSTORM COVERAGE WILL SLOWLY INCREASE THROUGH THE
EVENING AS WAVE APPROACHES WITH A CLUSTER OF SHOWERS AND
THUNDERSTORMS MOVING INTO THE MISSOURI VALLEY AROUND SUNSET AND
REACHING I90 BEFORE MIDNIGHT. WITH ALMOST NO CAPPING
INVERSION...THESE SHOWERS AND STORMS WILL CONTINUE DEVELOP AND MOVE
NORTHEAST THROUGH THE NIGHT. WITH WIDESPREAD STORMS...SEVERE
WEATHER IS UNLIKELY EXCEPT AHEAD OF THE MAIN CLUSTER OF STORMS IN
THE EVENING...ASSUMING ENOUGH INSTABILITY IS PRESENT TO PRODUCE A
STRONG ENOUGH UPDRAFT TO SUPPORT MARGINALLY SEVERE HAIL. AS NOTED
ABOVE...THIS THREAT IS VERY CONDITIONAL AND UNCERTAIN AS CAPES BY
EVENING WILL LIKELY BE AT OR BELOW 1000 J/KG. INSTEAD EXPECTING A
WIDESPREAD 0.5 TO 1.0 INCH OF RAIN SATURDAY NIGHT. LOCAL AMOUNTS
COULD EXCEED 1.5 INCHES IN PORTIONS OF THE AREA. WITH THE CLOUDS
AND PRECIPITATION LOWS WILL BE AROUND 60.

ON SUNDAY...SHOWERS AND STORMS WILL LINGER INTO THE
MORNING...ESPECIALLY NORTH OF I90. THEN A DRY SLOT WILL MOVE OVER
THE AREA WHICH SHOULD BRING A RESPITE TO THE PRECIPITATION TO MOST
AREA. A DRY LINE IS THEN EXPECTED TO MOVE ACROSS THE AREA ON
SUNDAY MORNING. AT THIS POINT...HAVE LOW POPS WITH THE DRY LINE
AS UPPER FORCING FOR ASCENT IS MINIMAL AND ATMOSPHERE WILL BE
FAIRLY STABLE FOLLOWING THE OVERNIGHT CONVECTION. A COLD FRONT
WILL MOVE ACROSS SUNDAY AFTERNOON. WITH LIMITED MOISTURE...
PRECIPITATION WILL NOT BE AS WIDESPREAD AND IS EXPECTED TO BE
FOCUSED CLOSER TO THE UPPER LOW MOVING ACROSS CENTRAL SD AND
EASTERN ND. SO HAVE THE HIGHEST POPS NORTH OF INTERSTATE 90. WHILE
THUNDER IS POSSIBLE WITH ANY STORMS...WITH THE LIMITED INSTABILITY
AND MOISTURE...HAVE PRIMARILY RAIN SHOWERS WITH A LOWER
PROBABILITY OF THUNDER. HIGHS WILL BE IN THE MID 70S WHERE THE
COLD FRONT WILL MOVE THROUGH IN THE LATE AFTERNOON...WITH MID 60S
IN CENTRAL SOUTH DAKOTA WHERE THERE WILL BE MORE CLOUDS AND MUCH
EARLY COLD FRONTAL PASSAGE.

FROM SUNDAY AFTERNOON INTO MONDAY EVENING...THE FOCUS WILL SHIFT
FOR RAIN TO WIND AND COLD. ONCE THE COLD FRONT MOVES THROUGH
SUNDAY AFTERNOON...NORTHWEST WIND WILL REALLY INCREASE WITH GUSTS
WELL ABOVE 30 MPH BY SUNDAY EVENING. WINDS WILL DROP LITTLE ON
SUNDAY NIGHT AND THEN PICK BACK UP WITH SUSTAINED WINDS OVER 20
MPH ON MONDAY. TEMPERATURES WILL FALL FAIRLY QUICKLY SUNDAY NIGHT
WITH LOWS IN THE 30S TO LOW 40S. ON MONDAY...THERE WILL BE A LOT
OF LOW LEVEL MOISTURE AROUND SO EVEN IF THERE IS SOME BREAKS IN
CLOUDS MONDAY MORNING...WITH 850 MB TEMPS BELOW ZERO...SUNSHINE
WILL BE SELF DESTRUCTIVE AND SKIES IN MOST AREA WILL BECOME CLOUDY
BY LATE MORNING. MOST PLACES WILL LIKELY REACH HIGHS IN THE 40S TO
MID 50S BY EARLY AFTERNOON AND THEN HOLDING STEADY. AT THIS POINT
THE GFS BUFR SOUNDINGS SHOW A VERY SHALLOW UNSTABLE LAYER SO NOT
EXPECTING SHOWERS TO DEVELOP BUT WILL NEED TO MONITOR THE
POTENTIAL AS NAM/ECMWF SOUNDINGS WOULD SUPPORT A MIX OF GRAUPAL
AND RAIN IN PORTIONS OF SW MN AND EAST CENTRAL SD.

IN THE LONGER RANGE...MONDAY NIGHT THROUGH FRIDAY...BELOW NORMAL
TEMPERATURES ARE EXPECTED TO CONTINUE. THE MODELS HAVE A GENERAL
AGREEMENT WITH A LONG WAVE TROUGH OVER THE AREA THROUGH THE WEEK.
THE BEST CHANCE OF RAIN WILL BE ON LATE TUESDAY NIGHT AND
WEDNESDAY BUT THERE IS SOME QUESTION HOW FAR EAST THE RAIN WILL
GET AS EASTERLY FLOW FROM HIGH PRESSURE WILL ACT TO LIMIT MOISTURE
FLOW INTO THE AREA AND MAY PREVENT RAIN FROM REACHING SW MN AND
PORTIONS OF NW IA. TEMPERATURES THROUGH WEDNESDAY WILL BE IN THE
50S WITH UNSEASONABLY COLD AIR BOTH DAYS AND CLOUDS AND RAIN ON
WEDNESDAY. A GRADUAL WARM UP WILL BEGIN ON THURSDAY AND CONTINUE
INTO FRIDAY ALTHOUGH IT IS MOST LIKELY HIGHS WILL REMAIN IN THE
60S. A STRONGER WAVE WILL ALSO APPROACH LATER FRIDAY WHICH MAY
BRING A CHANCE OF THUNDERSTORMS BY AFTERNOON. HOWEVER...THE BETTER
CHANCE WILL BE INTO MEMORIAL DAY WEEKEND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1222 PM CDT FRI MAY 15 2015

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO
THE AFTERNOON HOURS AS ELEVATED INSTABILITY LIFTS NORTHWARD AND
LIFT REMAINS ABUNDANT. GENERALLY...VFR CONDITIONS SHOULD
PREVAIL...OUTSIDE OF VERY OCCASIONAL LOWERING FROM PASSING SHOWERS.

VERY TRICKY FORECAST INTO THE OVERNIGHT AND DAYTIME HOURS OF
SATURDAY. MODEL CONSENSUS CONTINUES TO POINT TO LINGERING SHOWERS
IN THE EARLY EVENING AS STRONGER AND MORE WIDESPREAD CONVECTION
BLOSSOMS OVER WESTERN NE/SD. SHOULD AN ORGANIZED STORM CLUSTER
DEVELOP...FLOW VECTORS WOULD TAKE THIS ACTIVITY EASTWARD INTO THE
CWA AFTER MIDNIGHT.

WITH ABUNDANT MOISTURE AND AN INCREASING LLJ...WOULD ALSO
ANTICIPATE REDEVELOPMENT OF MVFR TO IFR STRATUS INTO SATURDAY
MORNING.


&&

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

$$

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



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