Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 241733
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1233 PM CDT SUN APR 24 2016

.UPDATE...
ISSUED AT 1229 PM CDT SUN APR 24 2016

STILL LOOKING FAVORABLE FOR SCATTERED SEVERE STORM DEVELOPMENT
THIS AFTERNOON AND EARLY EVENING. HAVE MADE A FEW MINOR SHORT TERM
CHANGES TO GRIDS...MAINLY TO ACCOUNT FOR MORE PERSISTENT
CLOUDINESS AND THE CONTINUE REGENERATION OF SHOWERS AND ISOLATED
THUNDERSTORMS ALONG THE LEADING EDGE OF PV ADVECTION FROM SOUTH
CENTRAL TO NORTHEAST NEBRASKA. WILL SEE EARLIER PRECIPITATION
FOCUSED ACROSS NW IA DWINDLE FOR MUCH OF THE AFTERNOON...IN FAVOR
OF THE MORE DYNAMICALLY FORCED AREA TO THE WEST. SOMEWHAT
CONCERNED WITH THE DEGREE OF CLOUDS AND IMPACT ON POTENTIAL
DESTABILIZATION.

DRYLINE CURRENTLY ARCING FROM EAST OF KICR AND KONL...TO EAST OF
KEAR...AND WILL BE WATCHING THIS FEATURE ANXIOUSLY THROUGH THE
AFTERNOON. AT THIS POINT...LOOKING FOR INSTABILITY TO TOP OUT
PERHAPS 1300-1500 J/KG IN A FAIRLY NARROW AXIS NEAR AND AHEAD OF
THIS FEATURE. AS MAIN LOBE OF PV ACROSS WESTERN KANSAS/NE LIFTS
NORTHEAST INTO THE AREA LATE AFTERNOON...SHOULD INITIATE MORE
VIGOROUS CONVECTION. SHEAR VECTORS ARE LARGELY ORTHOGONAL TO THE
BOUNDARY...SUGGESTING A MORE ISOLATED NATURE. FAIRLY STRONG SHEAR
WITH HODOGRAPHS AT LEAST LARGELY STRAIGHT...SO PERHAPS SOME
SPLITTING WITH LEFT MOVERS BACKING OFF THE BOUNDARY TO THE DRIER
SIDE. EXPECT THERE WILL BE A THREAT FOR ALL MODES OF SEVERE...
PRIMARILY HAIL WITH DECENT SHARE OF CAPE IN THE HAIL GROWTH ZONE.
HOWEVER... AGAIN HAVE HINTS IN MODELS THAT LOW LEVEL JET WILL
INCREASE EVEN LATE AFTERNOON AND EARLY EVENING AHEAD OF THE PV
ANOMALY AND AS A RESULT STRETCH OUT THE 0-1KM SHEAR QUITE A BIT BY
EARLY EVENING FOR A SLIGHTLY BETTER TORNADO THREAT IN THE 5 PM TO
8 PM WINDOW AS ACTIVITY SHIFTS GRADUALLY EAST FROM NEAR I-29 INTO
NW IA AND PARTS OF SW MN.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 347 AM CDT SUN APR 24 2016

VERY MILD START TO THE MORNING WITH STRONG SOUTHERLY FLOW AHEAD OF
THE DEEPENING LOW PRESSURE TO THE WEST. THIS WILL SET UP AN
INTERESTING DAY TODAY WITH A FEW SHOTS AND THUNDERSTORMS AND A FEW
THAT COULD BECOME SEVERE. AT 8Z...WATER VAPOR INDICATED LOW PRESSURE
DEEPENING ACROSS COLORADO WITH A PIECE OF ENERGY SPREADING EAST INTO
NEBRASKA. THIS HAS ALLOWED A FEW ELEVATED THUNDERSTORMS TO DEVELOP
OVER WESTERN NEBRASKA. THIS MID LEVEL CONVERGENCE AND ELEVATED MIXED
LAYER WILL TRANSITION EAST THROUGH THE EARLY MORNING HOURS WHICH
COULD ALLOW FOR SHOWERS AND A THUNDERSTORM OR TWO MAINLY ALONG AND
EAST OF INTERSTATE 29 THROUGH LATE MORNING. FROM LATE MORNING INTO
MID AFTERNOON NOT EXPECTING MUCH ACTIVITY AS THE SURFACE WARM FRONT
WILL BE NEAR HIGHWAY 14 OR JUST NORTH OF THERE WHILE A SURFACE DRY
LINE WILL MOVE INTO THE JAMES RIVER VALLEY. THESE WILL BE TWO
LOCATIONS THAT WILL NEED TO BE WATCHED FOR POTENTIAL THUNDERSTORMS
AS COOLER AIR ALOFT SPREADS INTO THE AREA AND AIDS IN WEAKENING THE
CAP BY MID TO LATE AFTERNOON. IF THESE TWO AREAS WERE TO REMAIN
CAPPED IT APPEARS THAT THE BETTER CHANCES FOR A MORE ORGANIZED
THUNDERSTORM THREAT WILL BE ACROSS PARTS OF NEBRASKA INTO
IOWA...JUST A BIT SOUTHEAST OF THE AREA...WHERE THE MAIN PV ANOMALY
WILL SPREAD EAST.

NOW...FOR THE CONDITIONAL THREAT FOR SEVERE WEATHER. SHEAR AND
INSTABILITY NOT TOO BAD...WITH CAPE VALUES POSSIBLY REACHING 1500
JKG OR SO. OF INTEREST AS WELL IS THE LOW LEVEL WIND SHEAR...WITH
THE 0 KM TO 1 KM BULK SHEAR AROUND 15 TO 20 KNOTS BETWEEN ABOUT THE
JAMES RIVER VALLEY AND THE BIG SIOUX RIVER VALLEY. THE REMAINDER OF
THE HODOGRAPH NOT PERFECT BUT IS SOMEWHAT UNIDIRECTIONAL FROM THE
SOUTHWEST FROM ABOUT 750MB TO 200MB AND INCREASES WITH HEIGHT BUT
WITH A LACK OF MOISTURE AND THE UNIDIRECTIONAL SPEED SHEAR IT DOES
SUPPORT DISCRETE CELLS AND POSSIBLY SPLITTING CELLS. THE BETTER
CHANCE FOR THUNDERSTORMS WILL BE OVER PARTS OF NORTHWEST IOWA BUT
THE POTENTIALLY BETTER CHANCE FOR ISOLATED SEVERE MAY END UP CLOSER
TO THE DRY LINE. FOR NOW THINKING HAIL UP TO GOLF BALL SIZED...60
MPH WINDS AND ISOLATED TORNADOES.

AS FOR TEMPERATURES...DID NOT CHANGE HIGHS MUCH TODAY AS IT STILL
LOOKS WARM AND A BIT BREEZY. WITH THE TRACK OF THE SURFACE LOW A
LITTLE FARTHER NORTH LOWS TONIGHT WERE RAISED...WITH MID 40S NEAR
HURON AND MID 50S NEAR STORM LAKE.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 347 AM CDT SUN APR 24 2016

AS THE UPPER LOW LIFTS NORTHEAST INTO CENTRAL AND EASTERN MINNESOTA
MONDAY EXPECT PRECIPITATION TO COME TO AN END ACROSS THE REGION.
STRATUS AROUND 900 MB WILL LIKELY HANG TOUGH THROUGHOUT THE DAY
LIMITING MIXING SOME. WITH THE WARMER AIR LINGERING LONGER IN THE
EAST...WARMED HIGHS ALONG AND EAST OF HIGHWAY 60 IN NORTHWEST IOWA
INTO SOUTHWEST MINNESOTA.

MONDAY NIGHT APPEARS TO BE COOL AND DRY AS NORTHEAST FLOW DRAWS
COOLER AIR INTO THE REGION.  THIS FLOW WILL BECOME EASTERLY
THROUGHOUT THE DAY ON TUESDAY AS THE NEXT SYSTEM MOVES INTO THE
REGION. WITH THE WAVE SLIGHTLY SLOWER THAN PREVIOUSLY
FORECAST...HAVE SLOWED POPS DOWN DURING THE DAY ON TUESDAY...BUT
RAISED POPS TO CATEGORICAL ACROSS MOST OF THE FORECAST AREA TUESDAY
NIGHT INTO WEDNESDAY MORNING.  AS LOW LEVEL MOISTURE INCREASES
THROUGHOUT THE NIGHT..ATMOSPHERE BECOMES INCREASINGLY UNSTABLE AND
COULD SEE ELEVATED THUNDERSTORMS DEVELOP AFTER MIDNIGHT TUESDAY
NIGHT. A LOT OF THE DIRECTIONAL AND SPEED SHEAR IS CONTAINED BELOW
THE INSTABILITY IN THE NEAR SURFACE LAYER...SO AM NOT EXPECTING
ANYTHING THAT DEVELOPS TO BE SEVERE.

PRECIPITATION IS EXPECTED TO LIFT NORTH THROUGHOUT THE DAY ON
WEDNESDAY AS INITIAL PIECE OF ENERGY MOVES THROUGH...HOWEVER...MAIN
UPPER LEVEL LOW LINGERS AROUND THROUGH AT LEAST THURSDAY CREATING
ADDITIONAL CHANCES FOR PRECIPITATION. THE SYSTEM CONTINUES TO BREAK
DOWN THROUGHOUT THE WEEK...AND EVENTUALLY SHEARS OUT AND SHIFTS
TOWARDS THE WESTERN GREAT LAKES REGION BY THE WEEKEND.

AT THAT POINT...ANOTHER SERIES OF PHASED DISTURBANCES BEGINS TO
APPROACH FROM THE WEST/SOUTHWEST.  APPEARS TO BE A FAIRLY WET WEEK
CAPPED OFF WITH A WET WEEKEND AS THIS SYSTEM AFFECTS THE AREA.
MODELS REALLY DIFFER ON HOW THE SYSTEM EVOLVES.  THE ECMWF SUGGESTS
THE NORTHERN PORTION OF THE WAVE WILL HOLD BACK TO THE WEST...AND
THE TRACK OF THE SOUTHERN WAVE WILL BE KEY.  THE GFS SUGGESTS SYSTEM
WILL SHIFT EASTWARD TOGETHER.  BOTH WOULD RESULT IN
PRECIPITATION...THOUGH THE FORMER SOLUTION WOULD RESULT IN MORE
INSTABILITY AND THE POTENTIAL FOR MORE PRECIPITATION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1229 PM CDT SUN APR 24 2016

THUNDERSTORM CHANCES WILL INCREASE BY LATE AFTERNOON...ESPECIALLY
FOR KFSD AND KSUX TERMINALS. A FEW SEVERE STORMS WITH LARGE HAIL
AND DAMAGING WINDS POSSIBLE...AND MORE GENERAL THUNDERSTORMS WILL
AS WELL BRIEFLY REDUCE CONDITIONS INTO THE MVFR VISIBILITY/CEILING
RANGE. OTHERWISE...VERY LATE NIGHT AND EARLY MONDAY MORNING WILL
FIND IFR STRATUS WRAPPING SOUTHWARD THROUGH THE KHON AND
EVENTUALLY KFSD SITES.

&&

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

$$

UPDATE...CHAPMAN
SHORT TERM...08
LONG TERM...BT
AVIATION...CHAPMAN



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