Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 210012
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
612 PM CST THU NOV 20 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 348 PM CST THU NOV 20 2014

STRATUS HAS HUNG TOUGH ACROSS THE MISSOURI RIVER VALLEY ALL
DAY...AND IS EXPECTED TO EXPAND OVERNIGHT TONIGHT AS THE SURFACE
RIDGE SHIFTS EAST AND SOUTHERLY FLOW INCREASES.  WITH INCREASING
CLOUD COVER FROM WEST TO EAST...HAVE RAISED FORECAST LOWS ACROSS THE
EAST.  EXPECT FAIRLY STEADY IF NOT SLIGHTLY WARMING TEMPERATURES AS
CLOUDS INCREASE.

CLOUDS WILL LINGER ACROSS THE AREA THROUGH THE DAY ON FRIDAY.
QUESTION REMAINS AS TO WHETHER THERE WILL BE ANY DRIZZLE WITH
STRATUS...BUT SOUNDINGS SUGGEST STRATUS WILL REMAIN FAIRLY THIN
THROUGH MUCH OF THE DAY SO HAVE LEFT MENTION OF PRECIPITATION OUT
FOR NOW. STRATUS IS EXPECTED TO THICKEN THROUGHOUT THE DAY ON
FRIDAY...SO WILL NEED TO KEEP AN EYE ON THE POTENTIAL FOR DRIZZLE ON
FRIDAY EVENING AHEAD OF A WEAK TROUGH. HAVE SIDED WITH ISOTHERMAL
HIGHS FROM 00Z SAT 925 TEMPS...WHICH WARMS AREAS WEST OF A LINE FROM
HURON TO STORM LAKE ABOVE FREEZING.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 348 PM CST THU NOV 20 2014

THE LOW STRATUS PERSISTS INTO FRIDAY NIGHT AS THE WARM AIR ADVECTION
TRAPS LOW LEVEL MOISTURE BENEATH THE INVERSION. WITH THIS LAYER
POTENTIALLY BECOMING DEEPER OVERNIGHT...COULD SEE SOME DRIZZLE OR
FREEZING DRIZZLE DEVELOP...MAINLY ACROSS OUR EASTERN COUNTIES. BUT
WITH UNCERTAINTY IN WHETHER THE CLOUD LAYER WILL BECOME THICK
ENOUGH...WILL LEAVE OUT MENTION FOR NOW. WITH RELATIVELY BREEZY
SOUTHERLY WINDS - STRONGEST IN THE EAST - WARM AIR ADVECTION AND
OVERCAST SKIES WILL PREVENT TEMPERATURES FROM DROPPING MUCH AT ALL
OVERNIGHT. COULD EVEN SEE SOME READINGS RISE A LITTLE BIT IN THE
EARLY MORNING HOURS. LOWS WILL BE IN THE 20S OVERNIGHT.

MODELS SUGGEST THAT THE MAIN STRATUS LAYER GRADUALLY THINS FROM WEST
TO EAST DURING THE DAY ON SATURDAY. WITH A LIGHT SOUTHERLY FLOW AND
WARM AIR ALOFT AND A MILD START TO THE DAY...TEMPERATURES WARM INTO
THE MID 30S TO MID 40S. CLOUDS BUILD BACK INTO THE AREA SATURDAY
EVENING AND SATURDAY NIGHT AHEAD OF THE NEXT STORM SYSTEM.

ON SUNDAY...AN UPPER TROUGH MOVING ALONG THE NORTHERN STREAM DIGS
INTO THE NORTHERN HIGH PLAINS WHILE ANOTHER TROUGH MOVING THROUGH
THE SOUTHERN STREAM NEAR TEXAS LIFTS NORTHEASTWARD INTO THE MID
MISSISSIPPI VALLEY. MODELS EVENTUALLY PHASE THESE FEATURES OVER THE
WESTERN GREAT LAKES...QUITE A BIT FURTHER EAST THAN PREVIOUS RUNS.
WHILE THE UPPER LOW STILL BECOMES CUT OFF AND WOBBLES OVER THE UPPER
MIDWEST...THIS SYSTEM IS TRENDING WEAKER...PARTICULARLY FOR OUR
REGION. NORTHWEST WINDS WILL INCREASE TO AROUND 20 TO 30 MPH BEHIND
THE LOW ON SUNDAY. WHILE THE MAIN MOISTURE AND SUPPORT IS WELL EAST
OF THE AREA...SOME SCATTERED LIGHT SNOWFALL MAY DEVELOP ON THE BACK
SIDE OF THE LOW. NOT LOOKING AT MUCH IN THE WAY OF ACCUMULATION WITH
THE MOST RECENT MODEL RUNS...PERHAPS AN INCH OR LESS. WHILE
TEMPERATURES START OUT MILD ON SUNDAY WITH HIGHS MIXING BACK INTO
THE 30S...COLD AIR WRAPS BACK INTO THE REGION SUNDAY EVENING AND
STAYS BELOW FREEZING THROUGH THE REMAINDER OF THE PERIOD. RAIN MAY
MIX WITH SNOW INITIALLY ON SUNDAY AND SUNDAY EVENING...BUT CHANGE
OVER TO SNOW AS THE BETTER PRECIPITATION CHANCES ARRIVE ON MONDAY.
HIGHS ON MONDAY WILL BE IN THE 20S...AND WILL POSSIBLY SEE TEMPS
FALLING THROUGH THE DAY.

NOT MUCH OF ANY MODEL AGREEMENT HEADING INTO THE MIDDLE OF NEXT WEEK
WITH THE GFS AND ECMWF GETTING COMPLETELY OUT OF PHASE. THE GFS
BUILDS A LARGE RIDGE OVER THE INTERMOUNTAIN WEST AND SLOWLY NUDGES
EASTWARD...WHILE THE ECMWF IS FAR MORE PROGRESSIVE...KEEPING SEVERAL
WAVES MOVING ALONG THE WEST NORTHWEST UPPER FLOW. LEFT A LOW CHANCE
FOR LIGHT SNOW IN ON WEDNESDAY AND WEDNESDAY NIGHT WITH A
REINFORCING SHOT OF COLDER DAY. THANKSGIVING IS FAR MORE UNCERTAIN
WITH TEMPERATURES AS THE GFS BEGINS NUDGING THE RIDGE INTO THE HIGH
PLAINS WHILE THE ECMWF DROPS ANOTHER FRONT THROUGH THE AREA. DID NOT
ALTER FROM THE ALLBLEND SOLUTION WITH SUCH LOW CONFIDENCE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 610 PM CST THU NOV 20 2014

STILL SEEING A NARROW BAND OF MVFR STRATUS STRETCHING FROM
NORTHWEST TO SOUTHEAST FROM JUST NORTH OF CHAMBERLAIN TO JUST
SOUTH OF SIOUX CITY. AS WINDS IN THE CLOUD LAYER INCREASE THIS
EVENING OUT OF THE SOUTH AND SOUTHWEST...EXPECT THIS NARROW BAND
OF STRATUS TO MOVE NORTHEAST ACROSS THE CWA. STILL SOME
UNCERTAINTY ON IF IT HOLDS TOGETHER OR DISSIPATES...BUT FOR NOW
WILL GO WITH A FEW HOUR WINDOW OF MVFR CIGS AT THE TAF SITES AS
THIS MOVES NORTHEAST.

NAM AND GFS SHOW HIGH LEVELS OF LOW LEVEL MOISTURE INTO TOMORROW
AS WELL AS WARM AIR ADVECTS INTO THE AREA. AT THIS TIME FEEL THIS
IS MOST LIKELY A MODEL ERROR IN HANDLING THE WARMER AIR MOVING IN
OVER THE SNOWPACK...AND FAVOR A SOLUTION WITHOUT LOW LEVEL
STRATUS...AT LEAST THROUGH 0Z. SO WILL GO WITH VFR CONDITIONS AT
THE TAF SITES. STILL A CHANCE WE SEE LOW STRATUS...BUT THINK
PROBABILITY IS PRETTY LOW...BUT SOMETHING TO WATCH.

&&

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

$$

SHORT TERM...
LONG TERM...
AVIATION...CHENARD



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