Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 251732
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1132 AM CST THU DEC 25 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 352 AM CST THU DEC 25 2014

THE FIRST SNOW EVENT WILL NUDGE ITS WAY INTO THE NORTHERN AND
WESTERN EDGES OF OUR FORECAST AREA THIS MORNING. THE NEW 06Z NAM
SUGGESTS A FASTER START WITH AN INCH OR SO FROM HURON WEST SOUTHWEST
THIS MORNING...BUT THIS IS FASTER THAN THE PREVAILING MODEL
CONSENSUS AND EVEN IF THAT SNOW MATERIALIZES...A BUNCH WILL BE SPENT
ON MOISTENING AND COOLING THE LOW TO MID LEVELS. OTHERWISE...THE
OUTLOOK THROUGH TONIGHT IS FOR 2 OR 3 INCHES OVER THE FAR WESTERN
EDGE AND PERHAPS EAST A BIT TO NEAR DE SMET IN KINGSBURY CO...WITH
CHAMBERLAIN POSSIBLY GETTING CLOSE TO THE 4 INCHES. WITH NORTHERLY
WINDS PICKING UP MODESTLY BUT NOT ENOUGH TO CAUSE MORE THAN MINOR
DRIFTING...HAVE ELECTED TO NOT ISSUE A WINTER WEATHER ADVISORY
FOR NOW. THE SNOW SHOULD SPREAD VERY SLOWLY SOUTHEAST THROUGH THIS
EVENING BEFORE IT BEGINS TO WEAKEN LATE TONIGHT AS IT TRIES TO
MOVE INTO THE SOUTHEASTERN FORECAST AREA...LOSING THE THERMAL
SUPPORT/FRONTOGENESIS IT HAS IN THE NORTHWEST TODAY. AT MID
LEVELS. DO NOT EXPECT THE SNOW TO MAKE IT INTO MUCH OF NORTHWEST
IOWA BY THE END OF TONIGHT. BTW...AM NOT GOING WITH ANY FREEZING
RAIN OR SLEET EARLY THIS MORNING AS THE FEELING IS THAT THE AIR
WILL BE COOLED AS IT IS MOISTENED...TO WHERE IT SHOULD BE SNOW BY
THE TIME IT REACHES THE SURFACE.

TEMPERATURES TODAY SHOULD CLIMB SLOWLY INTO THE LOWER 30S WEST AND
NORTH...AND A LITTLE MORE INTO THE UPPER 30S SOUTHEAST. STEADY BUT
SLOW COOLING TONIGHT WILL DRIVE READINGS BACK INTO THE 20S...
PERHAPS NEAR 20 NORTHWEST. REGARDLESS OF THE BREAKING UP OF THE SNOW
PATTERN LATER TONIGHT...LOW CLOUDS SHOULD BE WELL ENTRENCHED BY THEN.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 352 AM CST THU DEC 25 2014

WITH THE FIRST UPPER LEVEL WAVE CONTINUING TO MOVE NORTHEAST...THE
SNOWBAND WILL CONTINUE TO WEAKEN THROUGH THE MORNING. THE BEST
CHANCE FOR SNOW WILL BE ACROSS SOUTHWESTERN MINNESOTA AROUND
SUNRISE AND IT IS LIKELY THAT FOR MOST PLACES THERE WILL EITHER BE
NO SNOW OR JUST A FEW FLURRIES MUCH OF THE MORNING. HIGHS ON
FRIDAY WILL RANGE FROM THE MID 20S IN THE JAMES VALLEY TO THE
LOWER 30S OVER NORTHWEST IOWA.

A SECOND UPPER WAVE WILL BEGIN TO MOVE NORTH FRIDAY AFTERNOON. AS
IT DOES...THE CIRCULATION ASSOCIATED 700 TO 750 MB FRONT...WHICH
WILL BE SLOWLY MOVING SOUTH...WILL BEGIN TO INTENSIFY. SNOW IS
EXPECTED TO DEVELOP IN NORTHEASTERN NEBRASKA DURING THE AFTERNOON
AND SPREAD INTO FAR SOUTHEAST SOUTH DAKOTA AND NORTHWEST IOWA BY
SUNSET ON FRIDAY. AS THE UPPER WAVE MOVES ACROSS NORTHWEST IOWA ON
FRIDAY NIGHT...THE BAND IS EXPECTED TO BROADEN WITH A LARGE AREA
OF SNOW BY FRIDAY EVENING. BASED UPON THE CURRENT TRACK OF THE
UPPER WAVE AND LOCATION OF THE 700-750 MB FRONT... EXPECTING THAT
THE FRONTAL BAND WILL BE ALONG OR SOUTH OF A LINE FROM YANKTON TO
SIOUX FALLS TO WINDOM LINE...WITH THE MOST LIKELY LOCATION ACROSS
NORTHWESTERN IOWA AND NORTHEASTERN NEBRASKA FROM THE SIOUX CITY
METRO AREA TOWARD SPENCER. SINCE IT IS EXPECTED TO BE A FAIRLY
BROAD BAND AND ALSO FAST MOVING...EXPECT A RATHER LARGE AREA OF 1
TO 3 INCHES OF SNOW EXTENDING ACROSS ALL OF NORTHWEST IOWA AS WELL
AS ADJACENT AREAS OF SOUTH DAKOTA...MINNESOTA AND NEBRASKA. AS THE
WAVE MOVES NORTHEAST AFTER MIDNIGHT...THE BAND OF SNOW WILL SLOWLY
MOVE SOUTHEAST AND WEAKEN WITH LITTLE IF ANY SNOW EXPECTED AFTER
SUNRISE ON SATURDAY. COLD AIR WILL BE ADVECTED SOUTHWARD BEHIND
THIS WAVE AS NORTHERLY WINDS INCREASE. AS A RESULT...LOWS WILL BE
AROUND 10 ABOVE NORTH OF I90 IN SOUTH DAKOTA. WITH THE CLOUDS AND
SNOW...LOWS WILL REMAIN IN THE UPPER TEENS IN NORTHWEST IOWA.

A SURFACE RIDGE WILL MOVE SOUTH OF THE AREA ON SATURDAY WITH WINDS
GRADUALLY BACKING TO WEST DURING THE DAY. WHILE WESTERLY FLOW
WOULD USUALLY RESULT IN TEMPERATURES RISING WELL INTO THE 20S TO
AROUND 30...THE NEW SNOW COVER AND RATHER WEAK FLOW IS EXPECTED TO
KEEP HIGHS IN THE LOW TO MID 20S. BUT SKIES ARE EXPECTED TO BECOME
PARTLY TO MOSTLY SUNNY DURING THE DAY MEANING THAT MOST PEOPLE
SHOULD SEE AT LEAST SOME SUNSHINE BY SATURDAY AFTERNOON. ON
SATURDAY NIGHT...THE RIDGE WILL MOVE INTO THE MISSISSIPPI VALLEY
WITH WINDS TURNING TO SOUTHWEST. CLEAR SKIES WILL ALLOW FOR SOME
RADIATIVE COOLING BUT WITH THE LIGHT SOUTHWEST WINDS...LOWS WILL
BE NEAR NORMAL FROM 5 TO 15 ABOVE.

IN THE EXTENDED...SUNDAY THROUGH WEDNESDAY...THE MAIN STORY WILL
BE MUCH COLDER WEATHER...ESPECIALLY ON MONDAY AND TUESDAY. THERE
IS GENERAL MODEL AGREEMENT ON THE COOL DOWN...THE ONLY QUESTION IS
HOW COLD IT GETS AND IF THERE IS A LITTLE LIGHT SNOW BEFORE THE
CANADIAN AIR MOVES IN. ON SUNDAY...THE COLD FRONT IS EXPECTED TO
MOVE ACROSS THE AREA AND BE NEAR I-80 BY SUNSET. BECAUSE THE AIR
IS FAIRLY MILD JUST AHEAD OF THE FRONT...HIGHS SHOULD BE NEAR
NORMAL IN THE 20S...ALTHOUGH TEMPERATURE MAY FALL DURING THE
AFTERNOON NORTH OF I90. SINCE THIS IS A FEW DAYS OUT DID NOT
INCLUDE IN THE CURRENT FORECAST. CLOUDS WILL ALSO INCREASE BEHIND
THE FRONT AS A WEAK UPPER LEVEL WAVE APPROACHES. THIS WAVE WILL
BRING A LOW CHANCE OF SNOW...PRIMARILY SOUTH OF I90...FOR LATE
SUNDAY NIGHT AND MONDAY. AT THIS TIME...IT LOOKS LIKE
ACCUMULATIONS WILL BE LESS THAN AN INCH...WITH MOST PLACES MORE
LIKELY JUST SEEING FLURRIES.

THE CLOUDS WILL KEEP TEMPERATURES ABOVE ZERO ON SUNDAY NIGHT.
HOWEVER...AS COLD AIR CONTINUES TO MOVE SOUTH ON MONDAY...THERE
WILL BE LITTLE WARMING DURING THE DAY...LIKELY LESS THAN 5
DEGREES. AND WITH WINDS OF 10 TO 20 MPH...THE WIND CHILLS WILL BE
BELOW ZERO MOST OF THE DAY. TUESDAY LOOKS EVEN COLDER WITH HIGHS
FRO ZERO TO 10 ABOVE. WIND CHILLS ON TUESDAY MORNING WILL BE FROM
10 BELOW TO 20 BELOW. WEDNESDAY WILL SEE TEMPERATURES BEGIN TO
RECOVER AS WINDS TURN MORE WESTERLY. CURRENTLY ONLY HAVE HIGH
TEMPERATURES ABOUT 5 DEGREES WARMER THAN TUESDAY. THE 00Z ECMWF
DOES HINT THAT WARMER AIR MAY MOVE IN MORE QUICKLY WHICH COULD
MEAN TEMPERATURES A LITTLE CLOSER TO NORMAL WEDNESDAY AFTERNOON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1128 AM CST THU DEC 25 2014

MAIN SNOW BAND TAKING SHAPE FROM THE SOUTHCENTRAL SD THROUGH THE
SD HIGHWAY 14 CORRIDOR...WHICH INCLUDES KHON. EXPECT VSBYS AND CIG
RESTRICTIONS THROUGHOUT THE FORECAST PERIOD WITH A LITTLE
IMPROVEMENT LATE IN THE PERIOD AS MAIN DYNAMICS SHIFT EAST. MAY BE
TOUGH TO GET SNOW AT KFSD WITH NORTHERN SYSTEM TODAY AND TONIGHT.
BETTER CHANCE LOOKS TO BE WITH THE SOUTHERN SYSTEM TOMORROW...SO
ONLY INCLUDED A TEMPO GROUP AT 10Z TONIGHT AND BECOMING PREVAILING
AT 14Z. SIMILAR THINKING WITH KSUX AS WELL WITH MAIN
RESTRICTIONS AFTER TAF FORECAST PERIOD.

&&

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

$$

SHORT TERM...
LONG TERM...SCHUMACHER
AVIATION...HEITKAMP



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