Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 021723
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1223 PM CDT TUE SEP 2 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 403 AM CDT TUE SEP 2 2014

WAVE WILL EXIT TO OUR EAST THIS MORNING...GIVING WAY TO A MOSTLY
SUNNY DAY ACROSS THE REGION. TEMPERATURES ALOFT CONTINUE TO
WARM...BUT AS FLOW TURNS MORE SOUTHERLY...DO NOT THINK MIXING WILL
BE AS GOOD. EITHER WAY...MOST GUIDANCE SEEMS TOO LOW GIVEN MODEL 850
AND 925 MB TEMPERATURES...THUS CONTINUED ON THE WARM SIDE OF
GUIDANCE. LOOKING FOR UPPER 70S TO LOW 80S ACROSS THE AREA...WHICH
IS AROUND OR JUST ABOVE AVERAGE FOR THIS TIME OF YEAR.

LOW LEVEL JET PICKS UP TONIGHT...INCREASING THETA E ADVECTION AND
ISENTROPIC LIFT OVER THE REGION. INSTABILITY WILL INCREASE AS A
RESULT...ALTHOUGH EXPECT THE LOWER LEVELS TO REMAIN CAPPED AS
WARMER TEMPERATURES ALOFT ADVECT IN AS WELL. THUS LOOKING LIKE ANY
CONVECTIVE ACTIVITY WILL PROBABLY END UP BASED AROUND 800 MB OR
SO. MODEL CONSENSUS SUGGESTS BEST CHANCE OF SEEING SOME ELEVATED
SHOWER OR THUNDERSTORM ACTIVITY WILL BE ALONG AND NORTHEAST OF A
HURON TO SIOUX FALLS TO STORM LAKE LINE. BASED ON LOW LEVEL JET
LOCATION AND ORIENTATION THIS MAKES SENSE AS WELL...SO FOCUSED
POPS IN THIS AREA. THINK ACTIVITY WILL PROBABLY JUST REMAIN
ISOLATED TO SCATTERED BETWEEN 3 AM AND 7 AM. NAM SEEMS OVERDONE
WITH INSTABILITY ORIGINATING FROM 800 MB...SUGGESTING OVER 2000
J/KG. GFS AND ECMWF SOLUTIONS SEEM MORE REASONABLE...WITH 1000
J/KG OR LESS OF ELEVATED CAPE. STORMS WILL BE BASED ABOVE THE BEST
SHEAR AS WELL...SO OTHER THAN MAYBE SOME SMALL HAIL...WOULD NOT
EXPECT ANYTHING TOO STRONG THROUGH 12Z. WITH SOUTHERLY FLOW
INCREASING OVERNIGHT...WARMED LOWS A FEW DEGREES INTO THE LOW TO
MID 60S.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 403 AM CDT TUE SEP 2 2014

LIKELY THAT ISOLATED TO SCATTERED NOCTURNAL ELEVATED CONVECTION
WILL BE ONGOING AT THE START OF WEDNESDAY OVER THE NORTHEAST HALF
OF THE CWA. NAM SOLUTION REJECTED FOR SEVERAL REASONS...NOT THE
LEAST BEING SOME VERY UNREALISTIC THERMODYNAMIC PROFILES...WHICH
ARE ALLOWING A MUCH FURTHER SOUTH DEVELOPMENT INTO THE APPROACHING
CAP. WILL WATCH MID LEVEL FOCUS FOR THIS CONVECTION PULL OFF TO
THE NORTHEAST DURING THE DAY. OTHER ISSUE WITH WEDNESDAY WILL BE
THREAT FOR STRATUS DEVELOPMENT EARLY MORNING TO PERSIST LONGER
INTO THE DAY IN THE EAST TO GREATLY IMPACT TEMPERATURES. EAST OF
I 29 LIKELY TO SEE VERY LIMITED SUNSHINE INTO EARLY AFTERNOON...
PERHAPS EVEN A BIT MORE PESSIMISTIC THAN GOING FORECAST. AREAS TO
THE WEST WILL BE POISED TO HOLD ON TO OR BREAK OUT INTO SUNSHINE
MUCH EARLIER...WITH TEMPS VARYING FROM LOWER 80S EAST TO LOWER 90S
WEST BY AFTERNOON. VERY STRONG CAP INDICATED BY WEDNESDAY
AFTERNOON...SO HARD TO PICTURE BEING ABLE TO CONTINUE ANY THREAT
OF CONVECTION PAST A SMALL CHANCE MIDDAY FOR EVACUATING HIGH BASED
STORMS ON NOSE OF THE 7-9C/KM MID LEVEL LAPSE RATES.

STRONG PACIFIC NW WAVE WILL START TO KNOCK DOWN THE FLAT RIDGING
ACROSS THE NORTHERN PLAINS BY LATER WEDNESDAY NIGHT...WITH
CYCLOGENESIS ACROSS THE NORTHERN PLAINS...DRAGGING A FAIRLY STRONG
COLD FRONT TOWARD THE I 29 CORRIDOR BY EARLY THURSDAY MORNING.
BOUNDARY STRONGLY CAPPED AND CONVERGENCE LACKING...WITH DEEPER
DYNAMICAL LIFT FORCING LAGGING BEHIND WITH MID/HIGH LEVEL
MOISTURE. PROSPECT FOR ANY MEANINGFUL PRECIPITATION CHANCES ON
LATER THURSDAY AND THURSDAY NIGHT ARE REALLY NOT THERE...WITH JUST
A MINIMAL THREAT FOR A HIGHER BASED SHOWER OR EVEN LESS LIKELY A
THUNDERSTORM ALONG WITH DIV Q AXIS SLIPPING SOUTHEASTWARD BEHIND
BOUNDARY. LOW LEVEL FRONTAL BOUNDARY IS VERY WELL REMOVED TO THE
SOUTH OF THE AREA BY LATER AFTERNOON...WITH PERHAPS THE LEADING
HINT OF LOWER BASED DEVELOPMENT BY VERY LATE AFTERNOON OR EARLY
EVENING ALONG THE FAR SOUTHEAST CORNER OF THE CWA.

THE PERIOD FROM FRIDAY THROUGH SUNDAY WILL TRANSITION BACK TO
NORTHWESTERLY FLOW...WITH A LARGE COOL AREA OF HIGH PRESSURE
SETTLING THROUGH THE NORTHERN PLAINS. THIS WILL DRIVE BOUNDARY
SOUTHWARD...AND OTHER THAN A REMOTE CHANCE FOR A HIGH PLAINS
DEVELOPMENT TO BRUSH THE FAR SOUTHWEST CWA WITH AN ILL-TIMED
WEAK WAVE AROUND FRIDAY OR SATURDAY...WILL BE DRY AND QUITE
COOL...WITH HIGHS IN THE UPPER 60S TO LOWER 70S...AND LOWS IN
THE MID 40S TO LOWER 50S.

TRANSITION BACK TOWARD ZONAL TO WEAKLY SOUTHWEST FLOW TOWARD THE
END OF THE PERIOD...WITH LOW LEVEL SOUTHERLY FLOW INCREASING ALONG
WITH MOISTURE CONTENT OF AIR. WITH NORTHERN STREAM WAVE INDUCING
INCREASE LOWER TO MID LEVEL THETA E ADVECTION BY SUNDAY NIGHT AND
MONDAY...CONTINUED TO INDICATE A LOWER CHANCE FOR THUNDERSTORMS.
TEMPS START TO MODERATE WITH MORE CLOUDS AND INCREASED MOISTURE...
BUT STILL REMAIN BELOW NORMAL THROUGH MONDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1222 PM CDT TUE SEP 2 2014

MAIN ISSUE FOR TAFS ARE CONVECTION...POTENTIAL FOR LOW LEVEL WIND
SHEAR AND LOW CLOUDS. THROUGH 06Z WED...VFR CONDITIONS EXPECTED
ALTHOUGH WINDS WILL GRADUALLY BACK TO SOUTHEAST IN ALL LOCATION IN
THE EVENING. AFTER 06Z...A STRENGTHENING LOW LEVEL JET AND
INCREASING INSTABILITY ARE EXPECTED TO RESULT IN THE DEVELOPMENT
OF THUNDERSTORMS PRIOR TO DAWN. WHILE A STORM IS POSSIBLE IN KFSD
OR KHON...THE BEST CHANCE WILL BE IN SW MN. THEREFORE DID NOT
INCLUDE TSRA IN TAF FOR EITHER SITE. HOWEVER...WITH A 40 TO 50 KT
LOW LEVEL JET FROM SOUTHEAST SD IN SW MN LATE TONIGHT AND EARLY
THU MORNING...THERE IS THE POTENTIAL FOR NON CONVECTIVE LOW LEVEL
WIND SHEAR. WITH CORE OF THE JET GOING THROUGH THE KFSD AREA...DID
ADD LOW LEVEL WIND SHEAR FOR SIOUX FALLS...BUT SUBSEQUENT SHIFTS
WILL NEED TO EXAMINE POTENTIAL IN KHON. THE OTHER CONCERN IS
DEVELOPMENT OF MVFR CEILINGS WEDNESDAY MORNING. ALL MODELS SHOW
MOISTURE INCREASING BELOW A FAIRLY STRONG INVERSION SO EXPECT CIGS
FROM 1000 TO 2000 FT TO DEVELOP AT KFSD AND KSUX SHORTLY AFTER
SUNRISE. WITH LESS MOISTURE EXPECTED AT KHON...KEPT VFR CONDITIONS
FOR NOW.

&&

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

$$

SHORT TERM...CHENARD
LONG TERM...CHAPMAN
AVIATION...SCHUMACHER


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