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000
FXUS63 KFSD 051818
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1218 PM CST THU DEC 5 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 320 AM CST THU DEC 5 2013

THE MAIN STORY TODAY WILL OBVIOUSLY BE THE WIND AND COLD. EARLY
TODAY...WINDS AT 925MB ARE A VERY BRISK 30 KNOTS AS COLD AIR
ADVECTION POURS IN. THEN THE 925MB WINDS DIMINISH TO 15 TO 20 KNOTS
DURING THE AFTERNOON HOURS. THEREFORE RELATIVELY SPEAKING...THE
SURFACE WINDS WILL LIKELY SUBSIDE A BIT THROUGH THE AFTERNOON...BUT
ANY WAY YOU SLICE IT...IT WILL BE NASTY OUT. NO REASON TO ALTER THE
WIND CHILL ADVISORY FOR TODAY WHICH BASICALLY ENCOMPASSES THE SNOW
COVERED AREAS. BUT DID DECIDE TO EXTEND IT SOUTHWARD ANOTHER ROW OF
COUNTIES SOUTHWARD FOR TONIGHT TO INCLUDE THE ENTIRE FORECAST AREA
EXCEPT THE SIOUX CITY TO STORM LAKE AREAS. EVEN SIOUX CITY AND STORM
LAKE HITS -20F FOR THEIR WIND CHILLS VERY LATE TONIGHT AND EARLY
FRIDAY...BUT FEEL AT THIS TIME IT IS NOT A LONG ENOUGH TIME FRAME TO
WARRANT A WIND CHILL HEADLINE FOR THOSE AREAS. CONCERNING AIR
TEMPERATURES...GENERALLY HAVE HIGHS MIXED TO ABOUT 925MB FOR TODAY.
AS WINDS CONTINUE TO DECREASE MORE TONIGHT COUPLED WITH CLEAR
SKIES...LOWS SHOULD EASILY RANGE FROM ABOUT -8 TO -14 DEGREES...
LIGHTLY WARMER IN OUR FAR SOUTHERN ZONES WHERE SNOW COVER IS LACKING.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 320 AM CST THU DEC 5 2013

THE MAIN ISSUE IN THE EXTENDED CONTINUES TO BE THE COLD USHERED
INTO THE UPPER MIDWEST UNDER NORTHWEST FLOW. FOLLOWED DAY SHIFT/S
TREND OF SIDING TOWARDS RAW GUIDANCE WITH LOW SUN ANGLE AND SNOW
COVER ACROSS MUCH OF THE FORECAST AREA...AND FOR THOSE AREAS THAT
ARE SNOW FREE AIRMASS WILL BE ADVECTING FROM SNOW PACK.

FRIDAY INTO FRIDAY NIGHT JUST LOOK DOWNRIGHT COLD WITH 925 HPA
TEMPS IN THE -20C TO -22C RANGE. WITH SNOW COVER AND WINDS
DECREASING...MIXING SHOULD BE RELATIVELY POOR SO SIDED WITH
FORECAST HIGHS JUST ABOVE ISOTHERMAL. FOR FRIDAY
NIGHT...CONSIDERED EXTENDING THE WIND CHILL ADVISORY ESPECIALLY
ACROSS THE EASTERN HALF OF THE FORECAST AREA WHERE NORTHWEST WINDS
HANG ON WITH THE BITTERLY COLD AIR MASS IN PLACE.
HOWEVER...DID NOT WANT TO COMPLICATE ADVISORY STATEMENT NOW WITH
SEVERAL STARTING AND ENDING TIMES FOR ONE MAIN MESSAGE OF COLD SO
OPTED TO HOLD OFF FOR NOW.

RETURN FLOW STARTS TO SET UP ON SATURDAY WITH THE NAM MORE
AGGRESSIVE THAT THE GFS WITH RETURNING MID-LEVEL MOISTURE.
SOUNDING PROFILES ARE NOTEWORTHY EARLY IN THE DAY AS THEY ARE
ENTIRELY COOLER THAN DENDRITIC ALL THE WAY UP TO THE
TROPOPAUSE...BUT WITH THE INCREASING SOUTHERLY FLOW WARM PROFILES
INTO THE DENDRITIC LAYER THROUGH SATURDAY AFTERNOON INTO SATURDAY
NIGHT. WITH WAVE EJECTING FROM THE SOUTHWEST AND VERY EFFICIENT
ATMOSPHERE...RAISED POPS INTO THE HIGH CHANCE/ LOW LIKELY RANGE
FOR WHAT WILL LIKELY BE A 18-20:1 SNOW. GREATEST ACCUMULATIONS
APPEAR TO BE ACROSS THE SOUTHERN HALF OF THE FORECAST AREA WHICH
WOULD ENSURE A WHITE HOLIDAY SEASON FOR ALL.

WHAT IS MOST SIGNIFICANT IS THE WINDS INCREASING SUNDAY NIGHT INTO
MONDAY INTO MONDAY NIGHT. WITH FRESH SNOW COVER THAT WILL BE THE
CONSISTENCY OF DRIER LINT...SNOW COULD CONTINUE TO BLOW AS 925 HPA
WINDS INCREASE TO 25-50 KNOTS OVER THE PERIOD. INCREASED WINDS IN
THE GRIDS...BUT DIDN`T/T WANT TO ADD BLOWING SNOW TO THE FORECAST ON
DAY 4 AT THIS POINT.

THEREAFTER...COLD PATTERN CONTINUES PERIODIC SHOTS OF COLD AIR
FROM THE NORTH. BOTH GFS AND ECMWF SHOW A BRIEF WARM UP ON
TUESDAY...BEFORE ANOTHER SHOT OF ARCTIC AIR RETURNS ON WEDNESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1217 PM CST THU DEC 5 2013

SOME FALSE CEILING ISSUES WITH AREAS AWOS/ASOS UNITS AT TIMES
DURING THE EARLY MORNING HOURS LIKELY DUE TO ICE CRYSTALS AND THE
STRONG INVERSION...SO EXPECT THE VFR CONDITIONS TO CONTINUE TO
PREVAIL ACROSS THE AREA THROUGH 18Z FRI. SOME SPOTTY MVFR CLOUDS
ARE LIKELY NEAR THE MISSOURI RIVER NORTH OF K9V9...LAKE EFFECT
CLOUDS FROM LAKE OAHE AND LAKE SHARPE...WHICH WILL DISSIPATE
TOWARD SUNSET AS WINDS DECREASE.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WIND CHILL ADVISORY UNTIL 6 PM CST FRIDAY FOR SDZ038>040-050-
     052>069.

     WIND CHILL ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST FRIDAY
     FOR SDZ070-071.

MN...WIND CHILL ADVISORY UNTIL 6 PM CST FRIDAY FOR MNZ071-072-080-081-
     089-090-097-098.

IA...WIND CHILL ADVISORY UNTIL 6 PM CST FRIDAY FOR IAZ001-002.

     WIND CHILL ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST FRIDAY
     FOR IAZ003-012>014.

NE...NONE.
&&

$$

SHORT TERM...MJ
LONG TERM...
AVIATION...CHAPMAN