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000
FXUS63 KFSD 020920 CCA
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
319 AM CST MON DEC 2 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 319 AM CST MON DEC 2 2013

EARLY THIS MORNING...THERE IS A WAVE PASSING TO THE NORTH RESULTING
IN SOME WEAK PRECIPITATION IN EAST CENTRAL SOUTH DAKOTA MOVING INTO
SOUTHWEST MINNESOTA. PRECIPITATION FALLS THROUGH A WARM LAYER ABOVE
THE SURFACE...WITH A SHALLOW SUBFREEZING LAYER NEAR THE SURFACE.
THE WARM LAYER IS UNSATURATED SO MUCH OF THE PRECIPITATION ALOFT MAY
NOT REACH THE SURFACE...BUT MAY HAVE A FEW SPRINKLES OR A SHORT
SHOWER ALONG THE HIGHWAY 14 CORRIDOR THROUGH 12Z.  WITH TEMPERATURES
THERE NEAR FREEZING...ANY PRECIPITATION CARRIES THE POTENTIAL TO BE
PROBLEMATIC.

OTHERWISE...EXPECT A RELATIVELY WARM AND MILD DAY ACROSS THE
FORECAST AREA TODAY WITH LIGHT SOUTHERLY FLOW PREVAILING.  STRONG
INVERSION ALOFT WILL KEEP ATMOSPHERE FROM BECOMING VERY WELL
MIXED...AND MID LEVEL CLOUDS WILL HAMPER INCOMING SOLAR RADIATION
SOME.  EXPECT SOME BREAKS IN THE MID CLOUDS THOUGH THROUGHOUT THE
DAY.

CLOUDS WILL BE ON THE INCREASE TONIGHT AHEAD OF A DEEPENING LOW
PRESSURE SYSTEM MOVING OUT OF THE NORTHERN ROCKIES.  MID AND UPPER
LEVEL SUPPORT BEGIN TO INCREASE ACROSS CENTRAL SOUTH DAKOTA LATE IN
THE NIGHT...BUT OTHERWISE...LITTLE IN THE WAY OF DYNAMICS PREVAIL
THROUGH MUCH OF THE NIGHT AND HAVE KEPT FORECAST DRY THROUGH 09Z.
THEREAFTER...FORECAST SOUNDINGS SHOW SOME LOW LEVEL SATURATION
IMMEDIATELY AHEAD OF THE APPROACHING COLD FRONT...AND WITH
TEMPERATURES NEAR FREEZING...ANY PRECIPITATION COULD ONCE AGAIN BE
PROBLEMATIC.  THERMO PROFILES ALOFT INDICATE MILD YET SUBSATURATED
AIR...SO QUESTION BECOMES WHETHER ANY PRECIPITATION WILL
DEVELOP...AND IF SO...WHAT IT WILL FALL AS IF IT REACHES THE
SURFACE.  FOR NOW...JUST HAVE A SLIGHT CHANCE OF RAIN OR FREEZING
RAIN MENTIONED BUT ANY PRECIPITATION WOULD BE VERY LIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 319 AM CST MON DEC 2 2013

MODELS CONTINUE TO TREND FASTER WITH THE SURGE OF COLD AIR AND
TUESDAY NOW UNDER THE GUN FOR POTENTIALLY COLDER TEMPERATURES.
HOWEVER WHAT IS INTERESTING IS AN OCCASIONAL BIAS OF THE GFS WHICH
COLLAPSES THE LEADING TROUGH AND ARCTIC SURGE WHILE THE ECMWF AND
ESPECIALLY THE NAM KEEP THESE TWO BOUNDARIES SEPARATE. IN THE PAST
IT SEEMS WHEN THE NAM AND ECMWF HINT AT THESE TWO BOUNDARIES THEY
GENERALLY VERIFY SO WILL LEAN A LITTLE MORE TOWARDS THE WINDS OF THE
NAM AND ECMWF. BUT UNFORTUNATELY THE NAM AND ECMWF ARE DIFFERENT
ENOUGH THAT BLENDING THESE TWO MODELS IS ALSO DIFFICULT AS THE ECMWF
HAS BEEN THE SLOWEST MODEL EACH RUN AND IS QUITE A BIT SLOWER ON
SHIFTING THE INVERTED TROUGH EAST. FOR NOW WILL GO WITH MAINLY
NORTHWEST WINDS GRADUALLY DEVELOP FROM WEST TO EAST THROUGH THE DAY.
THE MAIN UPPER LEVEL SUPPORT LOOKS TO BE TO THE NORTH OF THE AREA
HOWEVER THE CWA IS WITHIN A TRAILING LOBE OF INSTABILITY ALOFT BUT
FOR NOW THAT AREA OF INSTABILITY IS IN A FAIRLY DRY LAYER SO THE
THREAT FOR PRECIPITATION LOOKS TO BE SOMEWHAT SMALL. STILL LOOKING
LIKE A MAINLY RAIN OR SNOW THREAT FOR THE DAY TUESDAY AS THE INITIAL
PUSH OF COOLER AIR SURGES THROUGH BUT MIXING SHOULD SUPPORT
TEMPERATURES ABOVE FREEZING AT THE SURFACE SO NO REAL THREAT FOR
FREEZING PRECIPITATION. WILL HAVE A SMALL THREAT FOR LIGHT FREEZING
RAIN IN THE FAR NORTHERN CWA BEFORE 15Z BUT AFTER THAT A RAIN OR
SNOW THREAT. THIS CHANCE FOR RAIN OR SNOW SHOULD CHANGE TO ALL SNOW
BY TUESDAY EVENING WITH GRADUALLY DECREASING CHANCES INTO WEDNESDAY.
MODELS DIFFERENT ENOUGH POPS WILL REMAIN MID TO LOW RANGE AND
AMOUNTS WILL REMAIN LIGHT. STILL FEEL THAT THERE WILL BE A THREAT
FOR ABOUT 1 TO 3 INCHES OF SNOW BUT AT THIS TIME JUST NO WAY TO
REALLY SAY WHERE...BUT WILL KEEP THE SLIGHTLY HIGHER AMOUNTS IN THE
NORTHERN CWA.

THE COLDER DRIER AIR REALLY SETTLES IN BY WEDNESDAY EVENING AND NOT
EXPECTING ANY THREAT FOR SNOWFALL WEDNESDAY NIGHT THROUGH THURSDAY
NIGHT. WHILE A FEW FLURRIES MAY BE POSSIBLE THE THREAT IS PRETTY
LOW.

DID DECREASE HIGHS A BIT AGAIN ON WEDNESDAY WITH THE SURGING COLD
AIR...LOOKING AT MAINLY TEENS WITH A FEW LOWER 20S IN NORTHWEST
IOWA. WITH SOME WIND AND CLOUD COVER EXPECTED ON WEDNESDAY NIGHT DID
NOT GO TOO COLD BUT STILL PRETTY MUCH SINGLE DIGITS EVERYWHERE WITH
DIURNAL CHANGES ON THURSDAY ONLY ABOUT 5 DEGREES SO HIGHS IN THE
SINGLE DIGITS TO 10 TO 15 DEGREES. WITH THE NORTHWEST WINDS ON
THURSDAY A WIND CHILL ADVISORY NOT IMPOSSIBLE OVER THE NORTHERN TIER
OR TWO OF COUNTIES LATE WEDNESDAY NIGHT INTO THURSDAY MORNING.

IN THE OUTER PERIODS...FRIDAY THROUGH SUNDAY...COLD AIR REMAINS
FAIRLY ENTRENCHED OVER THE AREA AS AN UPPER LEVEL TROUGH CONTINUES
TO DIG TO THE WEST OF THE AREA. A WAVE DOES TRY TO DEVELOP AND MOVE
ACROSS THE AREA ON SUNDAY WHICH WILL BRING A NORTHWARD KINK OF LESS
COLD AIR INTO THE REGION. IF THIS PATTERN EVOLVES AS THE MODELS ARE
HINTING AT WE WOULD SEE A DECENT CHANCE FOR SNOW AS A FAIRLY STRONG
BAROCLINIC ZONE WOULD DEVELOP AND THERE WOULD BE THE POTENTIAL FOR A
FAIRLY DEEP DENDRITIC ZONE. ALL OF THIS IS PRETTY FAR OUT BUT SOME
OF THE IMPORTANT INGREDIENTS ARE BEING HINTED AT SO WILL BE
SOMETHING TO WATCH FOR. OTHERWISE BELOW NORMAL TEMPERATURES THROUGH
THE PERIOD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 941 PM CST SUN DEC 1 2013

WEAKER LEAD WAVE MOVING THROUGH MINNESOTA AND IOWA...WITH
SECONDARY SYSTEM RACING INTO NORTHWEST SOUTH DAKOTA. LIFT FORCING
WITH SECONDARY WAVE LOOKS TO REMAIN MAINLY NORTH AND EAST OF THE
TAF SITES...WITH POTENTIAL FOR PERHAPS A LITTLE LIGHT FREEZING
RAIN OR RAIN NEAR THE KHON SITE AROUND 07Z-11Z WINDOW.
HOWEVER...NOT WORTH A MENTION WITH VERY LOW PROBABILITY EVENT AT
THIS TIME. EVEN WITH A BIT BETTER THREAT OF PRECIPITATION TOWARD
SW MN...CONDITIONS ARE LIKELY TO REMAIN VFR EVEN IN ANY
PRECIPITATION...GREATER THAN 6 SM AND CEILINGS ABOVE 3000 FT AGL.

&&

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

$$

SHORT TERM...
LONG TERM...08
AVIATION...CHAPMAN