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000
FXUS63 KFSD 071118
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
518 AM CST SAT DEC 7 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 241 AM CST SAT DEC 7 2013

SOME INITIAL PATCHY MIDDLE CLOUDS WILL SPREAD ACROSS THE AREA TODAY
WITH THE MORE CONSISTENT INCREASING CLOUD COVER STARTING UP THIS
AFTERNOON. AM SLOWING THE DEVELOPMENT OF THE SNOW INTO THE AREA THIS
EVENING WITH THE CHANCE INCREASING STARTING FAR SOUTHWEST ABOUT
SUNSET AND SNOW BECOMING LIKELY SOUTH OF INTERSTATE 90 BY MIDNIGHT.
MODELS INDICATING INITIAL BROAD BUT FAIRLY WEAK ISENTROPIC LIFT
SPREADING OVER THE AREA FROM THE S/SSW...THEN AN ENHANCEMENT OF THE
LIFT SOUTHEAST LATE TONIGHT AS SHORT WAVE APPROACHES FROM THE SW.
ANY ACCUMULATIONS SHOULD BE QUITE LIGHT UNTIL THIS ENHANCEMENT
HAPPENS. STILL...THE PROBABILITY OF MEASURABLE SNOW WILL GO TO AT
LEAST LIKELY OVER ALL EXCEPT A FAR NORTHWEST STRIP...AND INCREASE TO
CERTAIN SOUTHEAST LATE TONIGHT WHERE THE UPPER SUPPORT COMBINES WITH
THE THERMAL ADVECTION. GUIDANCE QPF GRIDS LOOK FAIRLY GOOD FOR
TONIGHT. FOR NOW WILL GO FOR A 15 TO 1 SNOW/LIQUID RATIO. AT BEST
MARGINAL DENDRITIC SNOW EXPECTED SOUTHEAST LATE TONIGHT BUT THERE
WILL ALSO NOT BE MUCH WIND...SO THIS SEEMS LIKE A GOOD COMPROMISE.
BY LATE TONIGHT EXPECT AN INCH TO A LITTLE MORE SOUTH CENTRAL AND
SOUTHEAST...TO A LITTLE BELOW AN INCH NEAR INTERSTATE 90 EAST OF THE
JAMES RIVER...TO A HALF INCH NORTHEAST...WITH LESS FAR WEST.

TEMPERATURES WILL WARM...IF YOU CALL IT THAT...TO THE ZERO NORTH TO
12-13 SOUTHEAST THAT WE HAVE BEEN GOING FOR...DROP VERY SLIGHTLY
EARLY THIS EVENING...THEN STEADY OFF AND SLOWLY RISE THE REST OF
TONIGHT.

WILL KEEP THE WIND CHILL ADVISORY GOING FOR NOW FOR THIS MORNING BUT
WE SHOULD BE ABLE TO KILL IT A LITTLE EARLY AT LEAST SOUTH. WE HAVE
ALREADY BEEN STRETCHING IT AND ALLOWING IT TO STAY FOR THE EXTREME
COLD THOUGH WINDS ARE GOING PRETTY LIGHT...SO WILL LEAVE IT NOW FOR
CONSISTENCY. THIS IS NOT BAD GIVEN THAT IT IS OUR COLDEST SHOT SO
FAR AND A LITTLE EARLY INT HE SEASON TO BOOT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 241 AM CST SAT DEC 7 2013

THE CRUX OF THE SHORT WAVE ENERGY MOVES ACROSS OUR FORECAST AREA
ON SUNDAY...EXITING RAPIDLY SUNDAY EVENING...QUICKER THEN PREVIOUS
MODEL RUNS. THE ENTIRE FORECAST AREA IS DEEPLY SATURATED ON SUNDAY
WITH A FAIR AMOUNT OF WARM AIR ADVECTION IN THE 900MB TO 700MB
LAYER. THEN THE MOISTURE MAKES A QUICK EXIT FROM WEST TO EAST
SUNDAY NIGHT. NORTHWEST IA STILL APPEARS TO BE THE PRIMARY FOCUS
FOR THE HIGHEST AMOUNTS OF SNOWFALL. THAT AREA DOES HAVE A DECENT
AMOUNT OF ASCENT...COUPLED WITH A SURGE OF PV AT THE 1.5 PRESSURE
SURFACE AND EVEN A BIT OF MID LEVEL FRONTOGENESIS. THE SNOWFALL
ACROSS THE REST OF THE FORECAST AREA WILL BE LIGHTER AND PRIMARILY
DUE TO BROAD ISENTROPIC LIFT. FURTHERMORE CONCERNING NORTHWEST
IA...DENDRICITY FINALLY BECOMES ESTABLISHED AND THIS COULD ALSO
HELP TO ENHANCE SNOW AMOUNTS. TEMPERATURES ACROSS THE REST OF OUR
AREA APPEAR TOO COLD TO GET MUCH IN THE WAY OF DENDRITIC GROWTH.

WITH THE LATEST MODEL RUNS NOT SHOWING REALLY ANYTHING IN THE WAY
OF MAJOR CHANGES ON SUNDAY...SNOW AMOUNTS HAVE REMAINED ABOUT THE
SAME. IN NORTHWEST IA...NEW PROJECTED SNOW AMOUNTS ARE JUST A
BIT LESS DUE TO THE FASTER EXIT SUNDAY EVENING. BUT STILL...
NORTHWEST IA SHOULD GET 4 INCHES OR SLIGHTLY MORE OF SNOWFALL.
COORDINATED WITH OAX AND DMX ABOUT A POSSIBLY WINTER WEATHER
ADVISORY. BUT DUE TO A LACK OF WIND AND A LONG DURATION EVENT...
DECIDED TO HOLD OFF FOR NOW. SPEAKING OF WIND...THIS WILL NEED
WATCHED AS THE EVENT GETS CLOSE OR IS UPON US AS SOMETIMES SNOW
AMOUNTS WILL BE GREATER THAN THOUGHT. THIS IS DUE TO A LACK OF
WIND TEARING AT THE SNOW CRYSTALS AND LESS COMPACTION ON THE
GROUND. SOMETHING TO WATCH FOR.

CONCERNING TEMPERATURES...THEY WILL BEGIN TO MODERATE LATE
SATURDAY NIGHT AND CONTINUE MODERATING INTO SUNDAY. GIVEN THE
925MB TEMPERATURES AND CLOUD COVER HOLDING IN WHAT HEAT THERE IS...
HIGHS SHOULD AVERAGE ABOUT 12 DEGREES NORTH TO MID TEENS AROUND
SIOUX CITY AND STORM LAKE.

AS MENTIONED ABOVE...THE WAVE QUICKLY EXITS SUNDAY NIGHT WITH
MODEST COLD AIR ADVECTION. THE WIND WILL INCREASE WITH THE
SUBSIDENCE WHICH WILL HELP TO HOLD THE AIR TEMPERATURE UP
RELATIVELY SPEAKING. NOT ANTICIPATING LOWS COLDER THEN 10 BELOW
ANYWHERE...BUT THIS WILL BE FOLLOWED BY ANOTHER COLD DAY ON
MONDAY. WHEN THE TIME COMES...WE WILL LIKELY NEED ANOTHER WIND
CHILL ADVISORY FROM ABOUT 06Z TO 18Z MONDAY.

FURTHER OUT...THE MODELS ARE IN EXCELLENT AGREEMENT IN BRINGING
ANOTHER SHORT WAVE THROUGH OUR AREA MONDAY NIGHT AS IT DIVES DOWN
THE NORTHERLY UPPER FLOW FROM CANADA. MIXING SHOULD ACTUALLY WARM
TEMPERATURES JUST BEHIND THE WAVE PASSAGE MONDAY EVENING BEFORE
GETTING COLDER LATER MONDAY NIGHT. THIS WAVE PASSAGE IS DRY...BUT
MODEL CONSENSUS DOES SHOW ANOTHER WAVE DIVING THROUGH OUR AREA
TUESDAY NIGHT. THE LATEST ECMWF DOES HAVE LIGHT SNOW SPREAD ACROSS
OUR FORECAST AREA WITH THIS WAVE AS LOW AND MID LEVEL BAROCLINICITY
IS STRONG...SURGING IN ANOTHER SHOT OF COLD AIR. RIGHT NOW ONLY
HAVE SMALL POPS FROM YANKTON TO GREGORY COUNTY BUT THIS WILL NEED
TO BE WATCHED IN FUTURE MODEL RUNS. LATEST CONSENSUS RAW MODEL
VALUES FOR LOWS TUESDAY NIGHT ARE QUITE COLD...SO BLENDED THEM
INTO THE PREVIOUS FORECAST TO NOTCH DOWN LOWS.

BEHIND TUESDAY NIGHTS WAVE...WEDNESDAY WILL BE ANOTHER COLD
DAY...WITH HIGHS ABOUT 5 TO 10 DEGREES COLDER THEN TUESDAYS.
TEMPERATURES WILL THEN FINALLY MODERATE INTO THE 20S ON THURSDAY.
HOWEVER LATE THIS WEEK...BOTH THE ECMWF AND GFS ARE IN EXCELLENT
AGREEMENT IN GIVING OUR FORECAST AREA A GLANCING BLOW OF ARCTIC
AREA DUE TO ANOTHER VERY COLD HIGH MOVING SOUTHEASTWARD FROM
MANITOBA TO THE GREAT LAKES. IF THIS DOES INDEED PAN OUT...WE
WILL HAVE TO BEGIN A TREND OF LOWERING HIGHS ON FRIDAY IN FUTURE
FORECASTS BY ABOUT 5 TO 10 DEGREES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 518 AM CST SAT DEC 7 2013

VFR WILL CONTINUE THROUGH AT LEAST 08/03Z. FROM 08/03Z TO 08/12Z
CEILINGS 1-3K FEET AND VISIBILITIES 1-3SM IN SNOW WILL SPREAD OVER
THE AREA FROM THE SOUTH AND SOUTHWEST...LOWERING AT HON/FSD/SUX
TAF SITES 08/06Z-08Z. VISIBILITY WILL LIKELY LOWER BELOW 1SM IN
SNOW SOUTH INCLUDING SUX AFTER 08/08Z.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WIND CHILL ADVISORY UNTIL NOON CST TODAY FOR SDZ038>040-050-
     052>071.

MN...WIND CHILL ADVISORY UNTIL NOON CST TODAY FOR MNZ071-072-080-081-
     089-090-097-098.

IA...WIND CHILL ADVISORY UNTIL NOON CST TODAY FOR IAZ001>003-012>014.

     WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING FOR IAZ020>022-
     031-032.

NE...WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING FOR NEZ013-014.

&&

$$

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