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000
FXUS63 KFSD 090449
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1049 PM CST SUN DEC 8 2013

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 342 PM CST SUN DEC 8 2013

THE LIGHT SNOW ACROSS THE AREA WILL END FROM WEST TO EAST THIS
AFTERNOON INTO EARLY THIS EVENING. WITH SNOW CONTINUING TO
LIGHTEN...AND MOST OR ALL OF OUR SITES ABOVE 2 MILES IN
VISIBILITY...WILL GO AHEAD AND CANCEL THE WINTER WEATHER ADVISORY. A
SECONDARY AREA OF LIGHT SNOW ACROSS CENTRAL NEBRASKA MAY CLIP SIOUX
CITY TO STORM LAKE LATER THIS AFTERNOON AND EARLY EVENING...BUT
ADDITIONAL ACCUMULATIONS WOULD ONLY BE AROUND A TENTH OR TWO.
OTHERWISE MAIN ISSUE TONIGHT WILL BE THE PASSAGE OF ANOTHER ARCTIC
FRONT AND DANGEROUSLY COLD WIND CHILLS. TEMPERATURES AND WIND SPEED
FORECAST A BIT TRICKY. STRONG COLD AIR ADVECTION BEHIND THE FRONT
SHOULD ACT TO KEEP US MIXED...RESULTING IN BREEZY NORTHWEST WINDS
AND MORE OF A SLOWLY FALLING TEMPERATURE CURVE. BUT IF SKIES CLEAR
AND WE CAN DECOUPLE BEFORE THE STRONG COLD AIR ADVECTION KICKS
IN...WE COULD DROP OFF FASTER AND THUS OVERNIGHT LOWS WOULD BE
COLDER. KEPT THIS FORECAST MORE TOWARDS THE MIXED SOLUTION...BUT
EITHER SOLUTION SHOULD RESULT IN WIND CHILLS DROPPING INTO THE 20
BELOW TO 30 BELOW ZERO RANGE AFTER MIDNIGHT THROUGH MONDAY MORNING.
THUS THE GOING WIND CHILL ADVISORIES LOOK GOOD. TEMPERATURES WILL
SLOWLY WARM THROUGH THE DAY MONDAY...ALTHOUGH WIND CHILLS WILL
REMAIN IN THE SINGLE DIGITS BELOW ZERO TO TEENS BELOW ZERO THROUGH
MUCH OF THE AFTERNOON. AS THE SOUTHWESTERLY LOW LEVEL JET INCREASES
MONDAY EVENING AND A STRONG WARM AIR ADVECTION REGIME TAKES
OVER...SHOULD ACTUALLY SEE TEMPERATURES CONTINUE ON AN UPWARD
TREND....WITH THE HIGHS OCCURRING IN THE EVENING OR OVERNIGHT.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 342 PM CST SUN DEC 8 2013

MONDAY NIGHT WILL SEE A ROLLER COASTER OF TEMPERATURES. AS A BOUNDARY
MOVES THROUGH IN THE LATE AFTERNOON AND EVENING...WINDS WILL
SWITCH TO THE WEST AND INCREASING MIXING WHICH WILL HELP
TEMPERATURES RISE THROUGH THE EVENING TO 10 TO 20 DEGREES BY
MIDNIGHT. THEN AN ARCTIC BOUNDARY WILL DROP SOUTH AFTER MIDNIGHT
CAUSING TEMPERATURES TO FALL ONCE AGAIN...ESPECIALLY NORTH OF I90.
BY SUNRISE...TEMPERATURES WILL BE BACK IN THE SINGLE DIGITS ABOVE
ZERO NORTH OF I-90 WITH WIND CHILLS FROM 5 BELOW TO 15 BELOW ZERO.
IF THE COLD AIR MOVES IN EVEN FASTER...TEMPERATURES COULD BE EVEN
COLDER BY SUNRISE.

A WEAK UPPER LEVEL WAVE WILL APPROACH THE AREA ON TUESDAY
AFTERNOON AND TUESDAY NIGHT. CLOUDS WILL INCREASE FAIRLY RAPIDLY
THROUGH THE DAY AND SOME WARMER AIR WILL MOVE BACK IN...ESPECIALLY
IN SOUTHEAST SOUTH DAKOTA AND NORTHWEST IOWA WHERE HIGHS WILL WARM
INTO THE 20S WITH TEENS CONFINED TO SOUTHWEST MINNESOTA. SOME
LIGHT SNOW MAY MOVE INTO SOUTHEAST SOUTH DAKOTA LATE IN THE
AFTERNOON.

THE UPPER LEVEL PV ANOMALY MOVES PRIMARILY ALONG THE MISSOURI
RIVER INTO NORTHWEST IOWA WHERE IT WILL INTERACT WITH THE 700 MB
FRONT. THEREFORE...HAVE INCREASED POPS IN THIS AREA TO 40 PERCENT
BUT KEPT 30 PERCENT NORTH OF I90 SINCE THERE IS STILL SOME
UNCERTAINTY EXACTLY WHERE THE BOUNDARY WILL BE. MOISTURE IS
REALLY LIMITED AND IT IS ALSO PRETTY STABLE SO THAT SNOWFALL RATES
WILL BE LIGHT. IN ADDITION...THIS IS A FAST MOVING SYSTEMS SO
DURATION WILL ONLY A FEW HOURS. AS A RESULT ANY SNOWFALL IS
EXPECTED TO BE LESS THAN AN INCH. AS COLDER AIR COMES IN BEHIND
THE WAVE...TEMPERATURES WILL FALL BELOW ZERO IN MOST AREAS.

WEDNESDAY WILL BE ANOTHER COLD DAY AS HIGH PRESSURE MOVES OVER THE
AREA. THIS COMBINED WITH THE SNOW COVER WILL LIMIT ANY MIXING
THROUGH THE DAY. DURING MUCH OF THE DAY...TEMPERATURES WILL REMAIN
BELOW ZERO IN SW MN AND ADJACENT AREAS OF SOUTHEAST SD AND
NORTHWEST IOWA. WEST OF THE JAMES RIVER...WESTERLY FLOW WILL
DEVELOP IN THE AFTERNOON WHICH WILL BRING IN WARMER AIR AND HAVE
TEMPERATURES RISE INTO THE MID TEENS. THE WARM AIR WILL CONTINUE
TO MOVE EAST DURING THE EVENING WITH HIGH TEMPERATURES BEING
REACHED IN THE EARLY EVENING. AS SOUTHWEST WINDS INCREASE THROUGH
THE NIGHT... TEMPERATURES WILL CONTINUE RISE APPROACHING 10 ABOVE
ZERO BY SUNRISE. THERE IS THE POTENTIAL FOR VERY STRONG
WINDS...WITH GUSTS OVER 30 MPH...TUESDAY NIGHT DOWNSTREAM OF THE
BUFFALO RIDGE INCLUDING MARSHALL AND TRACY...AS A STRONG
SOUTHWESTERLY LOW LEVEL JET DEVELOPS BELOW THE INVERSION. IF THESE
WINDS DEVELOP...THERE COULD BE SOME BLOWING SNOW LATE WEDNESDAY
NIGHT IN THIS AREA.

FOR THURSDAY THROUGH SUNDAY...THE OVERALL SYNOPTIC SCALE PATTERN
IS SIMILAR WITH A GRADUALLY FLATTENING OF THE FLOW THAT WILL ALLOW
WARMER AIR INTO THE AREA BY SUNDAY. BOTH MODELS ALSO SHOW ANOTHER
ROUND OF CANADIAN AIR MOVING IN LATE THURSDAY NIGHT OR FRIDAY. WITH WARM
AIR RETURNING LATE FRIDAY OR SATURDAY. THE RETURNING WARM AIR MAY
BRING SOME LIGHT SNOW OR FLURRIES WITH IT.

WHILE THE LARGE SCALE IS SIMILAR...THERE ARE TIMING DIFFERENCES
ON THE ORDER OF 12 HOURS BETWEEN THE ECMWF AND GFS...AND THE ECMWF
IS A BIT STRONGER WITH THE COLD AIR AS WELL. WITH SNOW COVER ACROSS
THE ENTIRE AREA...THIS PRODUCES A LOT OF UNCERTAINTY ON
TEMPERATURES SINCE ANY PERIOD WHERE WINDS ARE LIGHT WILL REALLY
LIMIT MIXING AND MAKE IT TOUGH TO WARM MUCH...EVEN DURING THE DAY.
WHILE THE POTENTIAL EXISTS THAT EITHER FRIDAY OR SATURDAY OR BOTH
DAYS COULD BE MUCH COLDER...IN THE SINGLE DIGITS ABOVE ZERO FOR
HIGHS NORTH OF I90...THE LARGE AMOUNT OF UNCERTAINTY ON WHEN THE
COLDEST AIR MOVES IN AS WELL AS THE DEGREE OF CLOUD COVER...FAVORS
BEING MORE CONSERVATIVE AND KEEPING HIGHS IN THE TEENS TO LOWER
20S. REGARDLESS...SUNDAY LOOKS MUCH WARMER WITH HIGHS IN THE 20S
AND 30S. AT THIS POINT...THE MILD AIR LOOKS TO HANG AROUND INTO
EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1038 PM CST SUN DEC 8 2013

LOW CEILINGS IN NORTHWEST IOWA AND SOUTHWEST MN CONTINUE TO
IMPROVE IN THE WAKE OF A COLD FRONT...AND SHOULD BE VFR FOR THE
REMAINDER OF THE TAF PERIOD. THERE IS A CHANCE WE COULD SEE AN AREA
OF STRATUS MOVE INTO THE REGION TOWARDS THE END OF THE TAF
PERIOD AFTER 03Z/TUE...MAINLY NORTH OF I-90. BUT CONFIDENCE IN THE
TIMING IS UNCERTAIN...SO WILL LEAVE OUT OF HON AND FSD TAFS FOR NOW
BUT WILL NEED TO WATCH FUTURE MODEL RUNS. WINDS WILL BE FROM THE
NORTHWEST TONIGHT AROUND 10 TO 15 KT AND GRADUALLY TURN WEST THEN
SOUTH DURING THE DAY ON MONDAY.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WIND CHILL ADVISORY UNTIL NOON CST MONDAY FOR SDZ038>040-050-
     052>055-057>061-063>065.

     WIND CHILL ADVISORY FROM 3 AM TO NOON CST MONDAY FOR SDZ056-062-
     066>071.

MN...WIND CHILL ADVISORY FROM 3 AM TO NOON CST MONDAY FOR MNZ071-072-
     080-081-089-090-097-098.

IA...WIND CHILL ADVISORY FROM 3 AM TO NOON CST MONDAY FOR IAZ001>003-
     012>014-020>022-031-032.

NE...WIND CHILL ADVISORY FROM 3 AM TO NOON CST MONDAY FOR NEZ013-014.

&&

$$

SHORT TERM...CHENARD
LONG TERM...SCHUMACHER
AVIATION.../