Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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201
FXUS63 KFSD 061716
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1116 AM CST SAT FEB 6 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 433 AM CST SAT FEB 6 2016

EXPECT RELATIVELY QUIET PERIOD THROUGH THE REST OF THE TODAY AND
TONIGHT. MAIN CONCERN SHIFTS TO WINDS...FIRST IN SOUTHWEST FLOW
ACROSS HIGHER ELEVATIONS OF SOUTHWEST MINNESOTA TODAY...THEN
GENERAL INCREASING LOW LEVEL FLOW LATER TONIGHT AS STRONG LOW
BEGINS TO APPROACH NORTHERN MINNESOTA. FOR TODAY...HIGH RESOLUTION
MODELS INDICATE ENHANCED PRESSURE GRADIENT IN ALONG THE BUFFALO
RIDGE...RESULTING IN LOCALIZED STRONGER AREA OF WINDS ALONG AND
DOWNSLOPE OF THE RIDGE. CANNOT RULE OUT SOME AREAS OF DRIFTING
SNOW AT TIMES...BUT DO NOT ANTICIPATE VISIBILITY REDUCTIONS IN
BLOWING SNOW...ESPECIALLY WITH TEMPERATURES EXPECTED TO APPROACH
OR EXCEED FREEZING BY THE TIME THE WINDS REACH THEIR STRONGEST
THIS AFTERNOON.

FOR TONIGHT...SEE STRONGER WEST-NORTHWEST FLOW BEGIN TO DEVELOP
ABOVE THE SURFACE...WITH 45-50KTS INDICATED ACROSS THE NORTHWEST
HALF OF THE FORECAST AREA BY 06Z-09Z. HOWEVER...FORECAST SOUNDINGS
FROM BOTH GFS AND NAM SHOW THAT THE BOUNDARY LAYER REMAINS A BIT
DECOUPLED FROM THE STRONGER FLOW...WITH BETTER CONNECTION REMAINING
TO OUR NORTH/WEST WHERE PRESSURE RISES AND BROADER COLD ADVECTION
BEGIN TO AID IN MIXING. THUS WHILE WINDS WILL BE INCREASING THROUGH
THE EARLY MORNING...DO NOT SEE SPEEDS APPROACHING HEADLINE CRITERIA
PRIOR TO 12Z SUNDAY. WILL BE QUITE A MILD NIGHT THOUGH...WITH WINDS
AND FAIR AMOUNT OF BOUNDARY LAYER MOISTURE HOLDING TEMPERATURES IN
THE LOWER-MID 30S MOST AREAS THROUGH THE NIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 433 AM CST SAT FEB 6 2016

MOST SIGNIFICANT PERIOD OF THE FORECAST STARTS SUNDAY AND CONTINUES
INTO MONDAY...ASSOCIATED WITH A PERIOD OF INCREASED WINDS AS UPPER
LEVEL WAVE DEEPENS RAPIDLY DROPPING TOWARD THE WESTERN GREAT LAKES.
THE PATTERN OF PV WRAPPING ON SUNDAY IS ESPECIALLY CONCERNING
HEADING INTO LATER SUNDAY AFTERNOON AND EVENING...INDICATIVE OF AN
EXTREMELY DYNAMIC WAVE. WINDS ATOP THE MIXED LAYER INCREASE TO 45 TO
55 MPH BY AFTERNOON. A BIT TOWARD THE STABLE SIDE TO START SUNDAY...
BUT THIS CONDITIONS WILL NOT LAST TOO LONG WITH TENDENCY FOR
INCREASING LAPSE RATES.  BATTLE OF TWO BIASES IN LOW LEVEL WIND
FORECAST...THE NAM AND ITS TENDENCY TO OVERLY RESTRICT MIXING BY
MAINTAINING THE COLD POOL OVER SNOWFALL...AND THE GFS WHICH CAN DO
QUITE THE OPPOSITE WITH AN OVERFORECAST OF OFF SURFACE WINDS. NOT
OVERLY IMPRESSED AT DAYBREAK SUNDAY WITH POTENTIAL FOR HIGH WIND
WARNING CRITERIA...WHICH WILL LIKELY NEED THIS BETTER NEAR SURFACE
MIXING TO INITIATE STRONGER WINDS ALOFT REACHING THE SURFACE. THIS
DOES GRADUALLY BECOME MORE FAVORABLE BY LATER MORNING AND ESPECIALLY
AFTERNOON...WITH LAPSE RATES APPROACHING DRY ADIABATIC EVEN OVER
DEEPER SNOWCOVER. SHALLOW STEEP LAPSE RATES WILL ALSO CONTRIBUTE TO
THE DEVELOPMENT OF BANDED SNOW SHOWERS. MORE FAVORED AREA FOR SNOW
WILL SWEEP DOWN ACROSS THE NORTHEASTERN HALF OF THE CWA DURING THE
AFTERNOON AND EVENING HOURS...BUT EVEN THE WEST SHOULD DESTABILIZE
ENOUGH FOR ISOLATED TO SCATTERED SNOW SHOWERS. THERE HAD BEEN SOME
CONCERN THAT RAIN WOULD BE POSSIBLE ACROSS SOUTHWESTERN AREAS...BUT
AT THIS TIME APPEARS AS IF TEMPS ALOFT WILL COOL ENOUGH TO PRODUCE
ICE...AND THE WARMTH OF NEAR SURFACE LAYER WILL LIKELY NOT BE ENOUGH
TO MELT.

DEEP SNOWPACK IN PLACES...ALONG WITH VERY STRONG WINDS AND THE
THREAT OF NEW SNOWFALL BRINGS LIKELIHOOD OF SOME SEVERELY REDUCED
VISIBILITY...AND EVEN BLIZZARD CONDITIONS. MUCH OF CURRENT SNOW IS
LIKELY OF LIMITED USE TO DEGRADE VISIBILITY...ESPECIALLY WHERE TEMPS
WILL REACH WELL ABOVE FREEZING TODAY. ALSO AM EXPECTING THERE TO BE
SOME NEED FOR A NEW SNOW ACCUMULATION...TO AID ANY TURBULENT BREAKUP
OF SNOW CRUST. VISIBILITIES CERTAINLY WOULD BE LOWEST DURING TIMES
OF SNOWFALL...POTENTIALLY WORST DURING THAT PERIOD SUNDAY NIGHT
WHICH TIMES OUT WITH A SECONDARY COLD ADVECTION SURGE FOCUSED
ESPECIALLY THROUGH THE EASTERN CWA AS INTENSE LOW PRESSURE DROPS
SOUTHWARD THROUGH WISCONSIN.

HAVE MAINTAINED CURRENT WATCH STATUS FOR HIGH WINDS WEST AND
BLIZZARD EAST WHERE SNOWFALL POTENTIAL IS GREATER...BUT DID EXTEND
THE BLIZZARD WATCH THROUGH MONDAY MORNING AS WILL CONTINUE TO FIND
SOME SCATTERED SNOW SHOWERS...AND GUSTY WINDS 25 TO 40 MPH CYCLING
THROUGH THE REGION. WILL HAVE TO KEEP AN EYE ON THE AREAS WHICH
RECEIVED HEAVY SNOWFALL FROM LAST BLIZZARD NEAR LOWER MISSOURI
VALLEY...BUT AM COUNTING ON COMPACTION AND LESSER SNOWFALL TO KEEP
FROM REACHING A TRUE GROUND BLIZZARD. FAIRLY INEVITABLE THAT SOME
TYPE OF ADVISORY WILL EXIST BETWEEN THE TWO WATCH AREAS.

TUESDAY TO FRIDAY AM GENERALLY DEALING WITH EXISTENCE IN THE TIGHT
LOWER LEVEL BAROCLINIC ZONE...WHICH WILL WAVER SOME BACK AND FORTH
AS A COUPLE WAVES TRAVERSE THE NORTHWEST FLOW INTO THE NORTHERN
PLAINS. AS A RESULT...SEVERAL PULSES OF WARM AIR ADVECTION NOTED
ACROSS THIS THERMAL RIBBON WHICH COULD BE ENOUGH TO GENERATE AREAS
OF LIGHT SNOWFALL...BUT MODELS REALLY EXHIBIT LITTLE IN THE WAY OF A
FOCUS ON EITHER TIMING OR LOCATION. FORTUNATELY NO LATTER WEEK
SYSTEM WOULD APPEAR TO HAVE ANY GREAT IMPACT...SO NOT IMPORTANT TO
TRY AND HAMMER OUT DETAILS AT THIS POINT. SOME CONSENSUS OF A MUCH
COLDER PUSH AGAIN FRIDAY INTO SATURDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1107 AM CST SAT FEB 6 2016

RELATIVELY LIGHT SOUTHERLY WINDS THROUGH THE REMAINDER OF THE DAY
WITH MID CLOUDS STREAMING ACROSS THE REGION. OTHERWISE...WINDS
ALOFT WILL INCREASE THIS EVENING...RESULTING IN LOW LEVEL WIND
SHEAR AT ALL SITES THROUGH THE REMAINDER OF TONIGHT. BY SUNDAY
MORNING NORTHWESTERLY SURFACE WINDS WILL INCREASE...GUSTING TO
AROUND 30 KTS BY 15Z.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     SDZ038-050-052-053-057>060-063>065-068.

     BLIZZARD WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY MORNING FOR
     SDZ040.

MN...BLIZZARD WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY MORNING FOR
     MNZ071-072-080-081-089-090-097.

IA...BLIZZARD WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY MORNING FOR
     IAZ002-003-013-014-022.

NE...NONE.
&&

$$

SHORT TERM...JH
LONG TERM...CHAPMAN
AVIATION...JM



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