Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 291141
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
641 AM CDT MON SEP 29 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM CDT MON SEP 29 2014

SHOWERS DEVELOPING ALONG AND AHEAD OF BOUNDARY MOVING THROUGH THE
AREA THIS MORNING.  THIS BOUNDARY IS EXPECTED TO WORK SOUTH TOWARDS
THE HIGHWAY 20 CORRIDOR IN NORTHWEST IOWA AND STALL THROUGHOUT THE
DAY.  FAIR AMOUNT OF STRATUS AND COLD AIR ADVECTION ON THE NORTH
SIDE OF THE BOUNDARY.  WITH NORTHEAST WINDS AND PERSISTENT CLOUD
COVER...WILL BE A REAL STRUGGLE TO WARM TODAY AND UNDERCUT GUIDANCE
VALUES NORTH OF THE BOUNDARY.  SIOUX CITY WAS A REAL TOUGH
CALL...BUT FOR NOW APPEARS AS THOUGH THE AIRPORT WILL REMAIN SOUTH
OF THE BOUNDARY...SO SIDED WITH VALUES SLIGHTLY ABOVE GUIDANCE
THERE.

STRATUS REMAINS ACROSS THE AREA INTO MONDAY NIGHT AS WARM AIR
ADVECTION PRECIPITATION FOCUSES TO THE WEST.  COULD SEE SOME OF THIS
PRECIPITATION WORK INTO CENTRAL SOUTH DAKOTA AFTER 06Z. WITH WARM
AIR ADVECTION REMAINING FAIRLY CONTAINED...EXPECT SHOWER ACTIVITY TO
MAINLY REMAIN WEST OF THE JAMES RIVER THROUGH 12Z. ATMOSPHERE IS
WEAKLY UNSTABLE...BUT EXPECT ANY LIGHTNING/THUNDER TO BE VERY
LIMITED. WITH CLOUD COVER HANGING TOUGH AND WINDS INCREASING AS LOW
PRESSURE SYSTEM APPROACHES FROM THE WEST...SHRUNK DIURNAL RANGE
THROUGH THE OVERNIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 400 AM CDT MON SEP 29 2014

TUESDAY STILL LOOKS INTERESTING IN TERMS OF THUNDERSTORMS AND
SEVERE WEATHER CHANCES. STRONG UPPER LOW WITH ATTENDANT
NEGATIVELY TILTED SHORT WAVE MOVES FROM SOUTHWEST TO NORTHEAST
ACROSS OUR FORECAST AREA ROUGHLY FROM 18Z TO 03Z...WHERE IT EXITS
SOUTHWEST MN.

AT THIS TIME...AGREE WITH THE SPC SECOND DAY OUTLOOK IN GIVING
THE BEST CHANCES FOR SEVERE GENERALLY FROM I 29 AND WESTWARD. EAST
OF I 29...STABILITY PARAMETERS INCREASE AND THE SHORT WAVE TIMING
APPEARS TO BE NOT AS FAVORABLE FOR SEVERE WEATHER. BUT ALONG AND
WEST OF I 29...DECENT CURVATURE EXISTS IN THE LOW LEVELS BELOW
800MB...SO IF SOME THUNDERSTORM CELLS CAN TIE INTO THE SURFACE OR
BOUNDARY LAYER...THEY COULD GO SEVERE. CURRENT THOUGHTS ARE THAT
THE BIGGEST RISK OF SEVERE WEATHER IS IN TERMS OF WIND. BOTH MIXED
LAYER AND MOST UNSTABLE CAPES ALOFT ARE RATHER THIN AND NOT OVERLY
IMPRESSIVE...SUGGESTING BUOYANCY WILL BE LIMITED. IN ADDITION...
ANTICIPATING A LOT OF CLOUD COVER AHEAD OF A DRY SLOT WHICH WILL
RESIDE IN OUR SOUTHWEST ZONES ON THE SOUTHEAST FLANK OF THE UPPER
LOW IN CENTRAL SD. BUT WIND SPEEDS ARE AVERAGING NEAR 30 KNOTS
FROM I 29 TO THE JAMES RIVER VALLEY...INCREASING TO 45 TO 55 KNOTS
AT 500MB IN THE SAME AREA. FURTHERMORE...DECENT JET STREAK MOVES
NORTHWARD ON THE EAST SIDE OF THE UPPER LOW OF 75 KNOTS IN THE
SLIGHT RISK AREA...COUPLED WITH STRONG 1.5 PRESSURE ADVECTION AND
MODERATE MID LEVEL LAPSE RATES. JUST AHEAD OF THE DRY SLOT...
SEVERE STORMS COULD DEVELOP AS SOON AS EARLY AFTERNOON...GENERALLY
IN THE JAMES RIVER VALLEY...AND THEN MOVE NORTH TO NORTHEAST
TOWARD THE I 29 CORRIDOR IN THE AFTERNOON. IF AN ISOLATED TORNADO
DEVELOPS...IT WILL LIKELY HAVE TO BE IN THE INITIAL STAGES OF
DEVELOPMENT NEAR THE JAMES RIVER VALLEY...WHERE THE STRONGEST
DIFFERENTIAL HEATING WILL RESIDE AS WELL AS LOW LEVEL CURVATURE...
AS THERE IS AN ABSENCE OF A SURFACE BOUNDARY WHICH IS WELL TO THE
WEST OF OUR FORECAST AREA. THEN AS MENTIONED ABOVE...EAST OF I 29
WILL EXHIBIT A LOT OF CLOUD COVER AIDING STABILITY AS WELL AS THE
SHORT WAVE TIMING MOVING INTO THOSE AREAS WELL AFTER DARK.

TUESDAY WILL OF COURSE BE A BREEZY TO WINDY DAY...WITH HIGHS
RANGING FROM THE UPPER 60S TO MID 70S. MAY HAVE TO WATCH OUR
SOUTHWEST ZONES WHO MAY GET WARMER IF MORE CLEARING BREAKS OUT IN
THE DRY SLOT THAN ANTICIPATED. POPS ARE STILL LIKELY TUESDAY
EVENING ALONG THE SHORT WAVE IN MUCH OF NORTHWEST IA AND SOUTHWEST
MN...BEFORE QUIETING DOWN AFTER MIDNIGHT. LOWS WILL STILL BE MILD
IN THE 50S.

BY WEDNESDAY...THE UPPER LOW WHICH MOVES THROUGH CENTRAL SD ON
TUESDAY IS A DISTANT MEMORY AS IT RAPIDLY MOVES INTO CENTRAL
CANADA. HOWEVER MORE UPPER TROUGHING DIGS IN THE ROCKIES KEEPING
AN UNSTABLE UPPER FLOW GOING...AND A SURFACE COLD FRONT WILL HANG
UP IN NORTHWEST IA AHEAD OF THE UPPER TROUGH. THEREFORE RAINFALL
CHANCES WILL CONTINUE ALONG AND EAST OF A TYNDALL SD TO MARSHALL
MN LINE...WITH POSSIBLY A FEW LIGHT SHOWERS ALSO NUDGING INTO OUR
FAR SOUTHWEST ZONES. STABILITY IS GREATLY INCREASED ON WEDNESDAY
WHEN COMPARED TO TUESDAY...BUT THERE COULD BE SOME EMBEDDED
AFTERNOON ISOLATED STORMS IN SHOWER ACTIVITY ACROSS NORTHWEST IA
NEAR THE SURFACE BOUNDARY. HIGHS ON WEDNESDAY WILL BE SIMILAR TO
TUESDAY...BUT COOLER IN OUR WEST WHERE THE UPPER 60S WILL RESIDE
NEAR CHAMBERLAIN WHEN COOLER AIR BEGINS TO ADVECT IN THE
AFTERNOON.

IN THE EXTENDED...NOT A LOT GOING ON IN TERMS OF PRECIPITATION.
BUT THE BIG STORY WILL BE COOLER TEMPERATURES. WEDNESDAYS UPPER
TROUGH IN THE INTERMOUNTAIN WEST MOVES ACROSS OUR AREA LATE
WEDNESDAY NIGHT AND THURSDAY...WHICH WILL BE QUICKLY FOLLOWED BY A
COLD UPPER TROUGH MOVING THROUGH THURSDAY NIGHT. SO ONE MORE DAY
OF 65 TO 70 DEGREES IS DOABLE ON THURSDAY...FOLLOWED BY MUCH
COOLER TEMPERATURES BY FRIDAY BEHIND THURSDAY NIGHTS CANADIAN COLD
FRONT. BREEZY CONDITIONS WILL RESIDE THURSDAY NIGHT...AND WINDY
EAST OF THE JAMES RIVER ON FRIDAY. GIVEN THE LATEST GFS AND ECMWF
925-850MB TEMPERATURES ON FRIDAY...THE ALL BLEND GUIDANCE
TEMPERATURES LOOKED WARM...SO BLENDED SOME CONSENSUS RAW VALUES
INTO THE MIX AS THE RAW VALUES ARE QUITE CHILLY BUT SEEM
REASONABLE. PREFER TO KEEP THE HIGHS ONLY 55 TO 60 FOR NOW...BUT
DEPENDING ON STRATUS POTENTIAL...FRIDAY COULD BE QUITE THE RAW AND
CHILLY DAY...COOLER THAN WHAT WE HAVE. THEN THERE SHOULD BE A SLOW
WARMING TREND FRIDAY THROUGH SUNDAY WITH PLEASANT CONDITIONS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 641 AM CDT MON SEP 29 2014

PLENTY OF IFR TO LOWER END MVFR WILL EXIST THIS MORNING ALONG AND
NORTH OF INTERSTATE 90 AFFECTING THE KFSD AND KHON TAF SITES.
SIOUX CITY IS SITTING IN A MORE FAVORABLE REGIME AND AS LOW LEVEL
WINDS BECOME EASTERLY FOR THEIR AREA...IT IS QUITE POSSIBLE THEY
WILL ESCAPE THE STRATUS AND STAY VFR FOR THE DAY. MVFR SHOULD
LINGER OVER KHON AND KFSD EVEN THIS AFTERNOON...BUT THERE ARE SOME
INDICATIONS THAT KFSD MAY BREAK OUT TEMPORARILY THIS EVENING AS A
BIT OF DRIER AIR ENTRAINS IN FROM THE EAST...CAUSING SOME POSSIBLE
VFR CONDITIONS FOR A SHORT PERIOD OF TIME. BUT AFTER MIDNIGHT...
NAM AND GFS SOUNDINGS STRONGLY SUGGEST MVFR CEILINGS AT ALL TAF
SITES IN OUR FORECAST AREA. LEFT THINGS DRY THROUGH TONIGHT AS THE
THUNDERSTORM POTENTIAL WILL HOLD OFF UNTIL TUESDAY.

&&

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

$$

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



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