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000
FXUS63 KFSD 041723
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1123 AM CST WED DEC 4 2013

.UPDATE...
ISSUED AT 1122 AM CST WED DEC 4 2013

WINTER STORM CONTINUES TO ROLL ON ACROSS THE AREA THIS MORNING...
WITH WELL DEFINED SNOW BAND FROM JUST NORTH OF I 90 IN SW MN...
BACK THROUGH SOUTHEAST SOUTH DAKOTA. HAVE SEEN VISIBILITIES DROP
TO 1/4 TO 1/2 MILE IN HEAVIEST PART OF THE BAND...AND SOME RATES
BRIEFLY REACHING AROUND AN INCH OR SLIGHTLY MORE PER HOUR. TAIL
END OF DEEPER LIFT FORCING SLIDES PAST INTERSTATE 29 EARLY THIS
AFTERNOON...AND SHOULD CONTINUE TO SEE PRECIP AREA AND RATES DROP
OFF AS HEAD INTO THE AFTERNOON. TEMPS REMAIN QUITE DENDRITIC AND
WITH SHALLOW FORCED LIFT AND WOULD EXPECT EVEN AS THINGS DRY OUT
SOMEWHAT ALOFT...WILL STILL SEE AT LEAST SOME FLURRY TO VERY LIGHT
SNOW CONTINUING MANY LOCATIONS AFTER MORE STEADY AND ACCUMULATING
SNOWFALL PULLS OUT. ALMOST TROWAL LIKE AIRSTREAM KEEPING NORTHERN
PRECIP GOING INTO THE AFTERNOON...WRAPPING BACK THROUGH THE NORTH.
WINDS STARTING TO COME UP MORE ACROSS THE WEST...AND WILL
GRADUALLY TAKE MORE IMPORTANCE IN THE WINTRY SCENARIO. FOR THE
MOMENT...WINDS NOT CREATING SIGNIFICANT BLOWING SNOW ISSUES BASED
ON AREA WEBCAMS...PERHAPS AS LOW AS A MILE WHERE SNOW NOT FALLING
OUT WEST. TEMPS WILL CONTINUE THE DOWNWARD SPIRAL THROUGH THE DAY...
AND BIG STORY FROM THIS EVENING OUT TO THE START OF THE WEEKEND WILL
BE THE DANGEROUS WIND CHILLS OF -20 TO -30F.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 339 AM CST WED DEC 4 2013

CURRENTLY ACROSS NORTHWEST IOWA...VISIBILITIES RUNNING IN THE 1/4 TO
1/2 SM RANGE IN FOG.  AS NORTHWEST WINDS INCREASE...EXPECT FOG TO
SHIFT EAST BUT HAVE A SMALL DENSE FOG ADVISORY THROUGH 14Z TO COVER
THIS.

700 MB FRONTOGENETIC BAND CURRENTLY ACROSS THE NORTHWESTERN HALF OF
THE FORECAST AREA.  THIS BAND IS EXPECTED TO LIFT NORTHEAST THROUGH
THE MORNING HOURS...AND AS IT DOES SO PRECIPITATION INTENSITY SHOULD
DECREASE.  DON/T EXPECT SNOW TO ABATE ENTIRELY THOUGH...AS
ATMOSPHERE CONTINUES TO COOL ATMOSPHERE BECOMES INCREASINGLY
DENDRITIC.  WITH COOLER ATMOSPHERE...SNOW RATIOS SHOULD CONTINUE TO
CLIMB TOWARDS THE 20:1 RATIO THROUGHOUT THE AFTERNOON.  INCREASED
POPS THROUGH THE DAYTIME HOURS TODAY...BUT EXPECT A HIGH POP...LOW
QPF EVENT WITH WEAK LIFT IN A VERY DENDRITIC ATMOSPHERE.  AS FOR
TEMPERATURES...HAVE ALREADY SEEN CALENDAR HIGHS AND WILL LIKELY SEE
TEMPERATURES SLOWLY FALL THROUGHOUT THE DAY AS COLD AIR ADVECTION
CONTINUES.  WITH STRONG NORTHWEST WINDS AND RELATIVELY DRY
SNOW...WILL LIKELY SEE AREAS OF BLOWING SNOW THROUGH THE DAY.  WITH
THE COMBINATION OF BLOWING SNOW AND WIDESPREAD SNOW TOTALS OF 4-6
INCHES...WILL KEEP WINTER STORM WARNING GOING THROUGH THIS EVENING
DESPITE THE DECREASING INTENSITY OF ADDITIONAL SNOWFALL THROUGHOUT
THE DAY.  IF THE BLOWING AND DRIFTING IS NOT AS BAD AS
ANTICIPATED...DAY SHIFT MAY NEED TO CONSIDER REDUCING WARNING DOWN
TO ADVISORY LEVEL.

FOR TONIGHT...COULD SEE A FEW LINGERING FLURRIES ACROSS THE NORTH
THROUGH THE EVENING HOURS...OTHERWISE THE MAIN STORY WILL BE THE
WIND AND COLD. GIVEN WIND CHILLS WILL BE PROBLEMATIC FOR THE NEXT
FEW NIGHTS...WILL LET THE DAY SHIFT DECIDE HOW THEY WANT TO HANDLE
IT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 339 AM CST WED DEC 4 2013

ON THURSDAY...COLD UPPER LOW IS ELONGATED ALONG THE CANADIAN BORDER
WITH SURFACE ARCTIC HIGH PRESSURE DRAINING DOWN INTO THE PLAINS FROM
WESTERN CANADA. COLD AIR ADVECTION CONTINUES TO POUR IN WITH 925MB
TEMPERATURES ONLY FORECAST TO RANGE FROM -20C IN OUR NORTH...TO -18C
IN OUR SOUTH BY 00Z FRIDAY. THIS WILL PLACE HIGH TEMPERATURES IN THE
SINGLE DIGITS ABOVE ZERO FOR MANY AREAS...MINUS MUCH OF NORTHWEST
IOWA WHO MAY BE A BIT MODERATED AT 10 TO 15 DEGREES. ONE PROBLEMATIC
ITEM ON THURSDAY IS THAT BOTH THE NAM AND GFS STILL SHOW A HIGH
DEGREE OF MOISTURE BOTTLED UP IN THE 925MB-900MB LAYER. THE MILLION
DOLLAR QUESTION IS WHETHER THIS IS STRATOCUMULUS...OR IS IT JUST A
MODEL ARTIFACT OF COLD AIR. CURRENTLY THE THOUGHT IS THAT IT MAY BE
SOMEWHERE IN BETWEEN...AS THE SUBSIDENCE DOES NOT LOOK TO BE STRONG
ENOUGH TO HELP TO TOTALLY DRY OUT THE ATMOSPHERE JUST ABOVE THE
SURFACE. THAT SAID...DO NOT THINK IT WILL BE TOTALLY CLOUDY EITHER.
THIS MATTERS BECAUSE WITH TEMPERATURES AT -18C TO -20C IN THAT
LAYER...ICE CRYSTALS WILL BE AROUND AND ANY CLOUD COVER AT ALL WILL
LIKELY PRODUCE FLURRIES. FOR NOW...LEFT FLURRIES OUT OF THE FORECAST
UNTIL WE GET THROUGH THIS CURRENT SYSTEM...AND NOTING THAT IF
ANYTHING DOES FALL ON THURSDAY IT WILL NOT ACCUMULATE.

ON THURSDAY NIGHT...WIND CHILL ADVISORY HEADLINES WILL PROBABLY BE
NEEDED WHEN THE TIME COMES WITH READINGS FALLING TO ROUGHLY THE -20F
TO -30F RANGE BY LATE IN THE NIGHT. WITH COLD AIR ADVECTION
CONTINUING AS THE ARCTIC HIGH DROPS SOUTHWARD...THE WIND WILL
DEFINITELY BE FELT...NOT WINDY BY ANY STRETCH OF THE IMAGINATION...
BUT STRONG ENOUGH TO MEET HEADLINE CRITERIA. FRIDAY WILL BE THE
COLDEST DAY OF THE WEEK WITH 925MB TEMPERATURES DOWN TO AROUND -20C
TO -22C. THIS WILL PLACE HIGHS 3 TO 5 DEGREES COLDER THEN THURSDAYS
HIGHS...WITH SOME WIND CHILL ADVISORY HEADLINES LIKELY REMAINING IN
THE MORNING.

WITH WINDS BECOMING LIGHT FRIDAY NIGHT...LOWS STILL LOOK VERY COLD
WITH A LOT OF -5 TO -15F PRESENT. THE WARMEST READINGS AROUND SIOUX
CITY AND STORM LAKE ARE QUITE A CHALLENGE AS IF THEY GET ANY SNOW
COVER ALSO...LOWS THERE WILL LIKELY BE COLDER. SO FOR NOW...BANKING
ON THOSE AREAS NOT GETTING ENOUGH SNOW COVER TO WARRANT GOING
COLDER.

IN THE LONGER RANGE PORTION OF THE FORECAST...VARIOUS DETERMINISTIC
MODELS ARE IN PRETTY GOOD AGREEMENT IN PHASING THE NORTHERN AND
SOUTHERN STREAM UPPER TROUGHS THROUGHOUT THE INTERMOUNTAIN WEST THIS
WEEKEND. ULTIMATELY WHAT THIS DOES IS BRING UP SOME ISENTROPIC LIFT
ALONG THE SOUTHERN STREAM JET OVER THE ARCTIC LOW LEVEL AIR MASS.
THIS WILL THEREFORE SQUEEZE OUT A LIGHT SNOW POTENTIAL OVER THE AREA
MAINLY SATURDAY NIGHT AND SUNDAY...WINDING DOWN FROM WEST TO EAST
SUNDAY NIGHT. IT WILL CONTINUE TO BE VERY COLD THIS WEEKEND...
ALTHOUGH CLOUD COVER WILL KEEP THE LOWS UP RELATIVELY SPEAKING
SATURDAY NIGHT AND A BIT MORE MODERATED ON SUNDAY COMPARED TO WHAT
WE WILL HAVE LATE THIS WEEK. STILL...IT WAS A GOOD IDEA TO BLEND
THE NEW CONSENSUS ALL GUIDANCE WHICH IS COLDER THAN PREVIOUS MODEL
RUNS...INTO THE CURRENT ALL BLEND. THEREFORE TEMPERATURES ARE A BIT
COOLER THEN PREVIOUS FORECAST. THEN ON MONDAY AND TUESDAY...MORE
COLD AIR ADVECTION POURS IN AS THE NORTHERN STREAM JET TAKES OVER...
BRINGING ANOTHER REINFORCING ARCTIC HIGH DOWN INTO THE AREA. EARLY
NEXT WEEK...HIGHS LOOK TO BE ONLY IN THE SINGLE DIGITS AGAIN FOR
MOST LOCATIONS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1122 AM CST WED DEC 4 2013

VISIBILITIES WILL LINGER IFR WITHIN SNOWFALL ACROSS FAR EASTERN
SOUTH DAKOTA AND SOUTHWEST MINNESOTA...AND ALSO WHERE BLOWING SNOW
OCCURRING FROM THE JAMES VALLEY WESTWARD. GRADUALLY...THE MVFR TO
VFR CEILINGS WILL OVERTAKE THE AREA...AND VISIBILITIES WILL LIFT
THIS EVENING INTO VFR.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR SDZ068-
     069.

     WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR SDZ038>040-
     050-052>067.

MN...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR MNZ089-
     090.

     WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR MNZ071-072-
     080-081-097-098.

IA...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR IAZ001-
     002.

NE...NONE.
&&

$$

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