Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 011537
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1037 AM CDT SAT AUG 1 2015

.UPDATE...
ISSUED AT 1027 AM CDT SAT AUG 1 2015

INITIAL SHORTWAVE ENERGY SLIGHTLY STRONGER THAN MODEL GUIDANCE
ANTICIPATED OVERNIGHT...WITH LLJ CONTINUING TO DEVELOP SCATTERED
STORMS ALONG AN ELEVATED BOUNDARY OVER SOUTH CENTRAL SD AND INTO
NEBRASKA. SHORT TERM GUIDANCE CONTINUES TO INDICATE THAT AS THE
LEAD WAVE MOVES SOUTHEAST...THE LLJ WILL GRADUALLY BACK WESTWARD
BY EARLY AFTERNOON AND SHOULD TAPER OFF THIS CONVECTION. 12Z
NAM/GFS PERFORMING VERY POORLY WITH THIS CONVECTION.

SECONDARY SHORTWAVE NOW ENTERING WESTERN ND ARRIVING SLIGHTLY
SLOWER THAN ANTICIPATED...BUT ALREADY DEVELOPING A SFC LOW WEST
OF BISMARCK. A SFC WARM FRONT STRETCHES SOUTHEAST OF THIS
LOW...OVER NORTHEASTER SD AND INTO SW MN.

BIGGEST QUESTIONS FOR THE AFTERNOON HINGE ON THIS LINGERING CLOUD
COVER...AND GRADUAL MIXDOWN OF SLIGHTLY DRIER AIR ALOFT. NAM
AGAIN VERY UNRELIABLE WITH BOUNDARY LAYER MOISTURE AT 12Z...BUT
FEEL HRRR...EXP-HRRR AND RAP FAR TOO AGGRESSIVE WITH THE MIXDOWN.
NEVERTHELESS...FOCUS FOR CONVECTION MAY SHIFT SLIGHTLY THIS
AFTERNOON...ALONG ADVANCING WARM FRONT OVER MN AND NE SD...AND
ALONG DIFFERENTIAL HEATING AXIS ACROSS OUR SWRN COUNTIES. THE
TIMING OF THIS SECONDARY WAVE IS ALSO NOT AS FAVORABLE.

FOR NOW...HAVE ADJUSTED POPS SLIGHTLY...AND LOWERED TEMPERATURES A
HAIR IN THE FAR SOUTH AND SOUTHWEST. THERE STILL APPEARS TO BE
POTENTIAL FOR A FEW CLUSTERS OF STRONG STORMS LATER TODAY...BUT
AGAIN MESOSCALE DETAILS STILL NOT RESOLVED MAY DRIVE THIS
OPPORTUNITY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CDT SAT AUG 1 2015

A SHORT WAVE PRESENTLY LOCATED OVER EASTERN MONTANA EARLY THIS
MORNING WILL CONTINUE TO SLIDE SOUTHWARD TODAY ON A NORTHWESTERLY
UPPER LEVEL FLOW...AND WILL PLAY A PART IN OUR WEATHER FOR LATER
THIS AFTERNOON. CURRENT RADAR SHOWING A LINE OF SHOWERS AND
THUNDERSTORMS DEVELOPING THROUGH SOUTH CENTRAL SD INTO NORTH CENTRAL
NE ALONG AN INSTABILITY AXIS AS MIDLEVEL THETA E ADVECTION SPREADS
INTO THAT AREA OUT AHEAD OF THE AFOREMENTIONED WAVE. MAY SEE THESE
STORMS CONTINUE OVER THAT AREA THROUGH THE MID MORNING BEFORE THE
LOW LEVEL JET WEAKENS. AFTER THAT WILL MOST LIKELY SEE CONVECTIVE
ACTIVITY WANE INTO THE AFTERNOON AS A CAP STRENGTHENS ACROSS THE
AREA. BY AFTERNOON THE SHORTWAVE BEGINS TO EXERT INFLUENCE ON THE
REGION WITH COOLING TEMPERATURES ALOFT WEAKENING THE CAP. STILL
SEEING SOME MODEL DIFFERENCES WITH REGARD TO LOWER LEVEL MOISTURE
AND RESULTANT DIFFERENCES IN THE AMOUNT OF INSTABILITY DURING THE
AFTERNOON...THOUGH EITHER WAY THERE SHOULD BE SUFFICIENT CAPE AS
TEMPERATURES WARM INTO THE UPPER 80S TO LOWER 90S TO SUPPORT
VIGOROUS UPDRAFTS IN STORMS WHICH ARE EXPECTED TO DEVELOP BY LATE
AFTERNOON THROUGH THE LOWER MISSOURI RIVER VALLEY. THIS CONVECTIVE
ACTIVITY WILL THEN BECOME MORE FOCUSED IN NORTHWESTERN IOWA AND
PORTIONS OF SOUTHWESTERN MINNESOTA BY LATE AFTERNOON AND EVENING AS
A LOW LEVEL JET STRENGTHENS OVER THAT AREA. EFFECTIVE SHEAR VALUES
LOOK TO BE RUNNING IN EXCESS OF 40 KTS...SO SEVERE STORMS WILL BE A
POSSIBILITY WITH LARGE HAIL AND DAMAGING WINDS. THINKING THAT CANNOT
COMPLETELY RULE OUT AN ISOLATED TORNADO WITH INITIAL CONVECTIVE
DEVELOPMENT THROUGH THE LOWER MISSOURI RIVER VALLEY...WITH LOW LCL
HEIGHTS AND FAIRLY STRONG 0 TO 1 KM SHEAR.

WILL SEE ANY STORMS EVOLVE EASTWARD THROUGH THE EVENING AND EARLY
NIGHT TIME HOURS AS THE SHORTWAVE SLIDES INTO CENTRAL AND EASTERN
IOWA BY EARLY SUNDAY MORNING. SOUTHWESTERLY WINDS WILL NOT BE QUITE
AS LIGHT TONIGHT...AND IT WILL BE A MILD NIGHT WITH LOWS GENERALLY
MID TO UPPER 60S.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 340 AM CDT SAT AUG 1 2015

ON SUNDAY...THE COOL FRONT WILL MOVE ACROSS THE AREA...EXITING
NORTHWEST IOWA BY EARLY AFTERNOON. THIS WILL SHIFT WINDS TO THE
NORTHWEST AT 10 TO 20 MPH WITH GUSTS UP TO 30 MPH IN SW MN DURING
THE AFTERNOON. THIS WILL RESULT IN A WELL MIXED ATMOSPHERE.
DESPITE SOMEWHAT COOLER AIR ADVECTING IN AT LOW LEVEL...
TEMPERATURES ARE EXPECTED TO STILL WARM INTO THE MID 80S TO LOWER
90S DUE TO MIXING. THIS WILL ALSO MIX DOWN DRIER AIR WITH
AFTERNOON DEW POINTS IN THE LOWER 50S OVER MUCH OF SE SOUTH DAKOTA
AND SW MN DURING THE AFTERNOON. A LITTLE MORE MOISTURE CAN BE
EXPECTED IN NW IOWA. WINDS ARE EXPECTED TO DROP OFF QUICKLY ON
SUNDAY EVENING AND WITH FAIRLY DRY AIR IN PLACE MOST PLACES NORTH
OF I90 WILL SEE LOWS IN THE UPPER 50S WITH LOWER 60S SOUTH OF I90.

MODEL DIFFERENCES INCREASE ON MONDAY. THE NAM SHOWS A WEAK UPPER
LEVEL WAVE MOVING IN THE NORTHWEST FLOW. AS THIS WAVE MOVES INTO
THE SD...THE 850 MB BOUNDARY IS DRAWN NORTHWARD INTO FAR SOUTHERN
SOUTH DAKOTA AND NORTHERN IOWA. THE GFS AND 00Z ECMWF DO NOT
REALLY SHOW THIS WAVE AND INSTEAD HAVE A WEAK WAVE MOVE EAST OUT
OF COLORADO INTO THE HIGH PLAINS. AS A RESULT THE 850 MB BOUNDARY
REMAINS BETWEEN I80 AND HWY 20. HAVE GENERALLY SIDED WITH THIS
SOLUTION. AS A RESULT ON MONDAY...WHILE SKIES WILL BECOME PARTLY
CLOUDY NEAR THE MISSOURI RIVER AND INTO NW IA...IT WILL AGAIN BE
MOSTLY SUNNY ALONG AND NORTH OF I90. THERE WILL AGAIN BE DEEP
NORTHERLY FLOW IN THIS AREA AND THIS WILL RESULT IN A WELL MIXED
ATMOSPHERE. AFTERNOON DEW POINTS WILL FALL INTO THE LOWER 50S WITH
TEMPERATURES WARMING INTO THE LOW TO MID 80S. FARTHER SOUTH...WITH
A FEW MORE CLOUDS AND LESS MIXING...DEW POINTS WILL REMAIN IN THE
LOWER 60S WITH HIGHS GENERALLY IN THE MID 80S.

WITH SOME CONVERGENCE IN THE VICINITY OF THE BOUNDARY IN NRN
NEBRASKA AND LI/S AROUND -2...COULD SEE A FEW SHOWERS OR
THUNDERSTORMS DEVELOP NEAR THE MISSOURI RIVER LATE MONDAY MORNING
INTO MONDAY AFTERNOON. THE BEST CHANCE FOR PRECIPITATION WILL BE
MONDAY EVENING AS THE UPPER WAVE APPROACHES THE AREA. WHILE IT
APPEARS THE BEST CHANCE FOR PRECIPITATION WILL BE SOUTH OF HIGHWAY
20...GIVEN UNCERTAINTY IN THE LOCATION OF THE 850 MB FRONT...HAVE
SLIGHT CHANCE POPS AS FAR NORTH AS I90 ON MONDAY EVENING WITH 30
TO 40 PERCENT POPS AROUND SIOUX CITY AND STORM LAKE. WITH THE
BETTER CONVERGENCE SHIFTING TO THE SOUTH THROUGH THE NIGHT...THE
PRECIPITATION CHANCE SHOULD DECREASE AFTER MIDNIGHT.

FOR THE EXTENDED...TUESDAY THROUGH FRIDAY...THERE ARE NOT MAJOR
DIFFERENCES BETWEEN MODEL SOLUTIONS. THE GFS...ECMWF...GEFS AND
CANADIAN ALL SHOW AN UPPER LOW NEAR HUDSON BAY AND A RIDGE OVER THE
WESTERN US. THIS RIDGE GRADUALLY MOVES EAST THROUGH THE WEEK
ALTHOUGH A WEAK WAVE MOVING OVER THE RIDGE MID TO LATE WEEK WILL
PREVENT ANY WARMING ACROSS THE AREA. AND IT IS THIS WAVE THAT WILL
DEFINE ANY PRECIPITATION CHANCES. TUESDAY LOOKS PRIMARILY DRY
EXCEPT FOR THE POSSIBILITY OF THUNDERSTORMS IN THE MISSOURI
VALLEY IN THE LATE AFTERNOON AND EVENING WHERE THERE IS MORE
INSTABILITY. WITH LITTLE IF ANY RAINFALL...HIGHS WILL GENERALLY BE
IN THE LOWER 80S. WEDNESDAY WILL MOST LIKELY BE DRY AS WELL
ALTHOUGH THE FASTER ECMWF DOES BRING THE WAVE EAST BY LATE
WEDNESDAY AFTERNOON. FOR THIS REASON HAVE A SLIGHT CHANCE OF
THUNDERSTORMS ON WEDNESDAY. ALL MODELS BRING THIS WAVE THROUGH
LATER WEDNESDAY NIGHT AND THURSDAY WHEN THE BEST CHANCE FOR
THUNDERSTORMS EXIST. THUNDERSTORMS CHANCES DECREASE THURSDAY NIGHT
AND FRIDAY. WITH MORE CLOUDS AND THE CHANCE OF RAIN...HIGHS
WEDNESDAY THROUGH FRIDAY WILL GENERALLY BE IN THE UPPER 70S TO
LOWER 80S. LOWS WILL BE FROM THE UPPER 50S TO LOWER 60S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 617 AM CDT SAT AUG 1 2015

AREAS OF IFR FOG THROUGH THE LOWER MISSOURI RIVER VALLEY WILL
DISSIPATE AFTER 13Z. OTHERWISE...VFR CONDITIONS INTO THE AFTERNOON
WHEN SCATTERED THUNDERSTORMS WILL DEVELOP THROUGH THE LOWER JAMES
RIVER VALLEY/MISSOURI RIVER VALLEY. THESE THUNDERSTORMS WILL THEN
PUSH TO THE EAST THROUGH NORTHWESTERN IOWA DURING THE EVENING. THE
GREATER CHANCES OF STORMS WILL BE SOUTH OF INTERSTATE 90...AND
MENTIONED IN THE KFSD AN KSUX TAFS.


&&

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

$$

UPDATE...DUX
SHORT TERM...JM
LONG TERM...SCHUMACHER
AVIATION...JM


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