Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 241002
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
402 AM CST WED DEC 24 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 401 AM CST WED DEC 24 2014

BROAD AREA OF STRATUS CONTINUES TO SIT ACROSS THE REGION VERY EARLY
THIS MORNING...AND MODEL LOW LEVEL RH TIME SECTIONS WOULD INDICATE
IT WILL BE TOUGH TO BREAK TODAY WITH PERSISTENT LOW LEVEL MOISTURE
UNDER AN INVERSION. THE BETTER CHANCE OF SEEING SOME BREAKS IN THE
CLOUDS WILL BE IN OUR WEST DURING THE AFTERNOON AS THE 925 MB FLOW
TAKES ON A DRIER SOUTHWESTERLY FLOW. OTHERWISE...A WEAK SURFACE
RIDGE SLIDES ACROSS THE AREA TODAY. IN RESPONSE...WILL SEE WINDS
TREND DOWNWARD THROUGH THE DAY FROM WEST TO EAST AS THE RIDGE AXIS
BECOMES SITUATED ACROSS THE AREA AND THE GRADIENT WEAKENS. WITH THE
EXPECTED CLOUD COVER TEMPERATURES WILL NOT RECOVER MUCH FROM MORNING
LOWS WITH HIGHS MOSTLY LOWER 30S.

BY TONIGHT THE RIDGE PUSHES OFF TO THE EAST...AND MAY BE ABLE TO
BREAK UP MORE OF THE STRATUS WITH THE LOW LEVEL FLOW BECOMING
SOUTH/SOUTHWESTERLY. EVEN SO...WILL LIKELY MAINTAIN A GOOD BIT OF
CLOUD COVER ACROSS THE AREA AS MID CLOUDS BEGIN TO INCREASE OUT
AHEAD OF THE NEXT SYSTEM TO EFFECT THE REGION. IN A WARM AIR
ADVECTION REGIME...OVERNIGHT LOWS WILL REMAIN WELL ABOVE NORMAL FOR
THIS TIME OF YEAR...DROPPING INTO THE LOWER TO MID 20S.


.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 401 AM CST WED DEC 24 2014

THE MAIN CONCERN FOR THURSDAY AND FRIDAY WILL BE SNOW CHANCES AND
AMOUNTS. ALL MODELS AGREE ON A WEAK UPPER LEVEL WAVE ASSOCIATED
WITH A 300 MB JET STREAK MOVING ACROSS NEBRASKA AND INTO THE
GREAT LAKES. THEY ARE ALSO CONSISTENT ABOUT THE PRESENCE OF A
FAIRLY STRONG 700 MB FRONT ACROSS SD THURSDAY AND THURSDAY NIGHT
AND SLOWLY MOVING SOUTHEAST INTO IOWA AND NEBRASKA BY FRIDAY. MOISTURE
IS LIMITED WITH THIS SYSTEM BUT THE STABILITY IS RATHER LOW ABOVE
THE FRONTAL SURFACE...ESPECIALLY THURSDAY AND THURSDAY EVENING. AS
A RESULT EXPECT AS THE UPPER WAVE MOVES TO THE NORTHEAST ON
THURSDAY...A FAIRLY STRONG FRONTAL CIRCULATION WILL DEVELOP WITH A
BAND OF SNOW DEVELOPING FROM SOUTHWEST SOUTH DAKOTA INTO NORTHEAST
SOUTH DAKOTA BY EARLY AFTERNOON. THERE WILL BE A PERIOD WHERE THE
NEAR SURFACE LAYER WILL NEED TO SATURATE. BUT ONCE IT DOES LIGHT
SNOW SHOULD DEVELOP ALONG OR NORTH OF HIGHWAY 14 IN SOUTH DAKOTA
BY LATE MORNING OR AFTERNOON. THIS BAND LOOKS TO REMAIN ALONG OR
NORTH OF A CHAMBERLAIN TO MARSHALL LINE THROUGH 00Z FRIDAY...SO
GENERALLY WENT DRY SOUTH OF THAT LINE WITH POPS INCREASING TO 60
PERCENT AROUND HURON. THIS WILL ALSO IMPACT TEMPERATURES CHRISTMASDAY
AS CLOUDS NEAR THIS BOUNDARY AS WELL AS EASTERLY WINDS WILL KEEP
TEMPERATURES CLOSE TO FREEZING WHILE MID 30S TO LOWER 40S ARE
EXPECTED OVER THE REMAINDER OF THE AREA...THE WARMEST TEMPERATURES
EXPECTED IN NORTHWEST IOWA.

THE FIRST UPPER WAVE WILL MOVE ACROSS THE AREA THURSDAY NIGHT. AS
IT DOES THE BOUNDARY WILL SLOWLY MOVE SOUTHWARD BRINGING LIGHT
SNOW NORTH OF A LINE FROM LAKE ANDES TO SIOUX FALLS TO WINDOM
MINNESOTA. THE STABILITY DOES INCREASE THROUGH THE NIGHT SO EXPECT
THE BAND OF SNOW WILL BE BROADENING AND WEAKENING THROUGH THE
NIGHT WITH THE MOST SNOW EXPECTED NORTH OF INTERSTATE 90. THE
FIRST WAVE WILL THEN MOVE NORTHEAST ON FRIDAY MORNING WITH THE
BEST CHANCE OF SNOW OVER SOUTHWEST MINNESOTA. IT LOOKS LIKE THERE
WILL BE A PERIOD FRIDAY MORNING WHEN SNOW WILL REALLY DECREASE.
THE NAM ESSENTIALLY ENDS ANY SNOWFALL AT THAT POINT. HOWEVER...
THE GFS AND...TO A LESSER EXTENT...ECMWF BRING A SECOND WAVE
NORTHEAST THROUGH WESTERN IOWA AND INTO SOUTHEAST MINNESOTA. AS
THIS WAVE APPROACHES...THE 700 MB FRONT IS EXPECTED TO BE FARTHER
SOUTH FROM FAR SOUTHEAST SOUTH DAKOTA TO THE IOWA GREAT LAKES.
HAVE GENERALLY SIDED WITH THE ECMWF/GFS SOLUTION. EVEN SO...WITH
HIGHER STABILITY AND LESS CERTAINTY ON WHETHER THIS SECOND WAVE
MOVES AS THESE MODEL INDICATE...KEPT POPS AROUND 40 TO 50 PERCENT
FRIDAY AFTERNOON OVER MUCH OF NW IA...NE NEBRASKA AND ADJACENT
AREAS OF SD AND MN. THIS WAVE AND ASSOCIATED SNOWFALL IS EXPECTED
TO GRADUALLY MOVE EAST OF THE AREA ON FRIDAY NIGHT.

AT THIS TIME...SNOWFALL FOR THE ENTIRE EVENT WILL RANGE FROM LESS
THAN AN INCH OVER MOST OF NW IA TO 3 OR 4 INCHES AROUND HURON AND
BROOKINGS. AS NOTED ABOVE...AM MORE CONFIDENT ON THE SNOWFALL
AROUND HURON AND BROOKINGS THAN THE SNOW IN NW IA ON FRIDAY
AFTERNOON AND EVENING AND IT IS POSSIBLE AREAS SOUTH OF I90 AND
EAST OF THE JAMES RIVER COULD SEE LITTLE IF ANY SNOWFALL FROM THIS
SYSTEM.

TEMPERATURES ON CHRISTMAS NIGHT WILL REMAIN WARM WITH WIDESPREAD
CLOUD COVER. LOWS WILL RANGE FROM AROUND 20 NEAR HURON TO THE
UPPER 20S IN PORTIONS OF NORTHWEST IOWA. HIGHS ON FRIDAY WILL
RANGE FROM THE LOWER 20S IN HURON AND CHAMBERLAIN TO THE LOWER 30S
AROUND SIOUX CITY AND STORM LAKE.

IN THE EXTENDED...SATURDAY THROUGH TUESDAY...THE MAIN STORY WILL
BE THE CHANGE TO MUCH COLDER TEMPERATURES BY EARLY NEXT WEEK. THE
WEEKEND LOOKS COLDER THAN THE LAST COUPLE OF WEEKS BUT HIGHS WILL
STILL RANGE FROM THE UPPER TEENS AROUND HURON AND BROOKINGS TO THE
MID TO UPPER 20S IN THE MISSOURI VALLEY AND NORTHWEST IOWA. THEN
ALL LONG RANGE MODELS BRING A SIGNIFICANT SURGE OF ARCTIC AIR INTO
THE PLAINS BY EARLY NEXT WEEK. SO CONFIDENCE IS HIGH THAT
TEMPERATURES WILL BE WELL BELOW NORMAL BY NEXT TUESDAY...THE
QUESTION IS HOW COLD IT WILL BE. MONDAY WILL SEE HIGHS FROM 10 TO
15 ABOVE NORTH OF I90 WITH AROUND 20 NEAR SIOUX CITY. TUESDAY
LOOKS MUCH COLDER. BECAUSE IT IS STILL 6 DAYS OFF KEPT HIGHS
GENERALLY IN THE SINGLE DIGITS ABOVE ZERO BUT IT IS VERY POSSIBLE
THAT HIGHS MAY NOT EVEN REACH ZERO NORTH OF I90...ESPECIALLY WHERE
SNOW COVER EXISTS. WIND CHILLS MONDAY AND TUESDAY ALSO LOOK TO BE
BELOW ZERO WITH SOME PLACES LIKELY AT OR BELOW -20 BY TUESDAY
MORNING.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1112 PM CST TUE DEC 23 2014

CEILINGS ACROSS THE AREA WILL BE RIDING THE EDGE OF THE MVFR AND
IFR RANGE THROUGH MUCH OF THE NIGHT AND EARLY MORNING HOURS FOR
TAF SITES. LOWEST CEILINGS WILL LIKELY RAISE A BIT WITH MIXING
DURING BY LATE MORNING OR MIDDAY. APPEARS AS IF SHOULD SEE BREAK
INTO THE VFR CEILING RANGE AS WINDS FLOW ALOFT PICKS UP INCREASING
DEGREE OF WESTERLY COMPONENT AROUND KHON BY MIDDAY...AND MID TO
LATE AFTERNOON AT KFSD AND KSUX. IN ADDITION TO CEILINGS...MAY SEE
A FEW SURFACE WIND GUSTS APPROACH 25 KNOTS FOR THE NEXT FEW HOURS
FOR KFSD AND KSUX.


&&

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

$$

SHORT TERM...JM
LONG TERM...SCHUMACHER
AVIATION...CHAPMAN


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