Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 252318
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
518 PM CST TUE NOV 25 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 405 PM CST TUE NOV 25 2014

A STRONG UPPER LEVEL WAVE IS FORECAST TO MOVE FROM WESTERN NORTH
DAKOTA LATE THIS AFTERNOON INTO NORTHEAST NEBRASKA BY LATE TONIGHT
AND THEN INTO THE MID MISSISSIPPI VALLEY BY WEDNESDAY AFTERNOON.
THERE IS NOT SIGNIFICANT FRONTOGENESIS WITH THIS SYSTEM...INSTEAD
EXPECT A FAIRLY BROAD AREA OF LIGHT TO BRIEFLY MODERATE SNOWFALL TO
DEVELOP...SIMILAR TO WHAT IS CURRENTLY OCCURRING OVER CENTRAL
NORTH DAKOTA. HAVE TIMED THE LEADING EDGE OF THE SNOWFALL OF THE
PRESSURE GRADIENT ON THE 1.5 PV ANOMALY WHICH IS COINCIDENT WITH
THE LEADING EDGE OF DEEP ASCENT. THIS REACHES THE THE JAMES VALLEY
AROUND 00Z...I-29 AROUND 03Z...AND HWY 71 IN IA AND MN AROUND 06Z.
THE UPPER WAVE DEEPENS OVER ERN SD AND ERN NEBRASKA SO THAT THE
POSITIVE PV ADVECTION PERSISTS INTO WEDNESDAY MORNING OVER
PORTIONS OF SW MN AND NW IA. ACCUMULATING SNOW IS ONLY EXPECTED TO
LAST 3 OR 4 HOURS OVER MOST OF SE SD AND MOST OF NW IA...WHERE 1
TO 3 INCHES IS EXPECTED. HOWEVER...THERE LOOKS TO BE ACCUMULATING
SNOW FOR 6 TO 10 HOURS FROM CANBY DOWN TO SPIRIT LAKE IOWA. WITH
ONLY 1/4 OR 1/2 INCH PER HOUR EXPECTED...THAT WOULD RESULT 3 TO 4
INCHES OF SNOW.

THE SECOND ISSUE WITH THIS SYSTEM WILL BE THE WINDS. A STRONG COLD
FRONT WILL DROP SOUTH WITH THE LOW AS IT MOVES ACROSS THE AREA
OVERNIGHT. TO THE EAST OF THE LOW TRACK...WINDS WILL BE AROUND 10
MPH OUT OF THE SOUTHEAST.  BUT AS THE LOW MOVES INTO
SOUTHEAST...WINDS WILL SHIFT TO NORTHWEST AND WITH PRESSURE RISES
AS THE LOW MOVES AWAY...WINDS WILL QUICKLY INCREASE TO AROUND 20
MPH WITH GUSTS OVER 30 MPH. FOR MOST AREAS...THE WINDS ARE NOT
EXPECTED TO INCREASE UNTIL AFTER THE SNOW ENDS OR IS ABOUT TO END.
THIS WILL REALLY LIMIT THE AMOUNT OF SNOW THAT WILL BE LOFTED SUCH
THAT BLOWING SNOW WILL BE LIMITED TO ONLY A FEW WIDE OPEN
LOCATIONS FOR BRIEF PERIODS OF TIME. THE EXCEPTION WILL BE FROM
CANBY MN TO SPIRIT LAKE WHERE THE SNOW IS EXPECTED TO LINGER INTO
WEDNESDAY MORNING. WINDS WILL INCREASE DURING THE MORNING AND WITH
LIGHT SNOW EXPECTED AT THE TIME...THIS WILL BE MORE CONDUCIVE TO
BLOWING SNOW...ESPECIALLY BETWEEN 8 AM AND NOON. WHILE THERE COULD
BE FLURRIES OR LIGHT SNOW SHOWERS INTO THE AFTERNOON EAST OF
HIGHWAY 59...MOST OF THE TIME SHOULD BE DRY SUCH THAT THE THREAT
FOR BLOWING SNOW WILL DIMINISH.

WITH THE COMBINATION OF 3 TO 4 INCHES OF SNOW AND SOME BLOWING SNOW
ON WEDNESDAY MORNING...WILL ISSUE A WINTER WEATHER ADVISORY FOR
PORTIONS OF SOUTHWEST MINNESOTA AND INTO DICKINSON COUNTY IOWA. AS
FOR TEMPERATURES...THEY WILL ONLY SLOWLY FALL THROUGH LATE TONIGHT
DUE TO CLOUDS AND SNOW. HOWEVER...ONCE WINDS SHIFT TO
NORTHWEST...EXPECT TEMPERATURES TO RAPIDLY FALL INTO THE TEENS AND
LOWER 20S FROM LATE TONIGHT INTO WEDNESDAY MORNING. TEMPERATURES ARE
LIKELY TO BE STEADY OR FALL MOST OF WEDNESDAY AS WELL...ESPECIALLY
IN NW IA WHERE THE COLD AIR WILL NOT ARRIVE UNTIL AFTER SUNRISE.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 405 PM CST TUE NOV 25 2014

SURFACE RIDGE NOSING IN ACROSS THE CWA WEDNESDAY NIGHT WILL HELP
TO DIMINISH WINDS. SHOULD SET UP A FAIRLY CHILLY NIGHT...BUT
CHALLENGE WILL BE IN DIAGNOSING POTENTIAL EXTENT FOR CLEARING
SKIES TO MAXIMIZE IMPACT OF THE SNOWFALL FROM TONIGHT AND
WEDNESDAY. EXPECTATIONS OF A FAIR AMOUNT OF LINGERING CLOUDS IN
THE EAST TO START THE EVENING...AND SHIELD OF HIGHER CLOUDS
STREAMING ACROSS THE SOUTHWEST TWO THIRDS OF THE AREA. IN
ADDITION...LOW LEVEL BAROCLINIC BOUNDARY HANGS UP WITH A FEW LOWER
CLOUDS ACROSS THE FAR WEST...AND INITIATION OF WARM AIR ADVECTION
MAY KICK UP A COUPLE OF FLURRIES IN THE FAR WEST WHILE TEMPS IN
CLOUD LAYER REMAIN FAVORABLY COLD. OTHERWISE...EXPECT TEMPS TO
DIP BELOW ZERO THROUGH NORTHERN COUPLE OF TIERS...AND IF CAN
SUPERIMPOSE THE SNOW COVER...CALM WINDS AND CLEAR SKIES...COULD
PUSH 10 BELOW OR MORE AROUND BROOKINGS.

THANKSGIVING DAY SHOULD BE GENERALLY QUIET WEATHERWISE...AS THE
SURFACE RIDGE AND IMPOSED DRY AIR SLIPS EASTWARD...AND BAROCLINIC
ZONE SLOWLY TRANSLATES NORTHEAST. A COUPLE OF EARLY DAY FLURRIES
MAY CONTINUE IN THE WEST...BUT WEAKENING OF QG LIFT AND WARMING OF
TEMPS IN THE MORE MOIST AIR SHOULD SPELL AND END TO ANY FLURRY
THREAT. HOWEVER...BY LATE DAY...ADVANCING BAROCLINICITY WILL START
TO FEEL IMPACT OF NEXT WAVE MOVING OUT OF NORTH DAKOTA. LIFT
FORCING LOOKS TO INCREASE...AND WILL AGAIN SEE A THREAT FOR A FEW
FLURRIES TOWARD KBKX-KMML AREA. OVERALL A FAIRLY COOL DAY AS
THERMODYNAMIC PROFILES STABILIZE AT LOWER LEVELS WITH WARMING
ALOFT...A FAIRLY AMOUNT OF CLOUDS...AND A DEVELOPING SOUTHEAST
LOW LEVEL COMPONENT.

MASSIVELY WARMING TEMPERATURES ALOFT ON THURSDAY NIGHT SHOULD LEAD
TO NON-DIURNAL TRENDS. LEADING EDGE OF WARMING GENERATING ENOUGH
LIFT AND SATURATION TO SUPPORT PRECIPITATION ACROSS THE NORTHEAST
DURING THE EVENING. SUB INVERSION LAYER LOOKS TO REMAIN QUITE
MOIST THROUGH THE NIGHT AND INTO EARLY FRIDAY MORNING...BUT DEPTH
IS LIKELY TOO SHALLOW WITH LIFT EXPECTED ABOVE THE MOIST LAYER...
BUT A GREAT DEAL OF LOWER CLOUDS AS WELL AS A FREEZING DRIZZLE
AFTER SNOW CHANCE TAPERS OFF IS NOT ANTICIPATED.

FRIDAY THE WARMEST DAY OF THE WEEK AS ZONAL FLOW ALLOWS WARMER
TEMPS ALOFT TO SURGE EASTWARD ACROSS THE PLAINS. WILL HAVE SOME
ISSUES TO WARMING TO DEAL WITH INCLUDING POTENTIAL FOR CLOUDS AS
WELL AS THE EXISTING SNOW COVER...BUT FAIRLY CONSERVATIVE NUMBERS
SUGGEST GRADIENT FROM MID 30S WHERE GREATER SNOWFALL OCCURS
NORTHEAST TO THE LOWER 50S LOWER BRULE AREAS.

SOME IMPORTANT DIFFERENCE BEGIN TO EVOLVE BY FRIDAY NIGHT...WITH
WAVE EXPECTED TO RIDE ALONG ZONAL FLOW...DRIVING A SHARP ARCTIC
BOUNDARY SOUTHWARD. TIMING IS PRETTY SUSPECT AT THIS POINT...WHICH
LEAD TO POTENTIAL LARGE ERRORS IN TEMPS AS SOME RUNS TAKE FRONT
COMPLETELY THROUGH THE CWA BEFORE 12Z SAT...WHILE OTHERS GIVE AT
LEAST A PORTION OF THE CWA OR DAY IN THE WARMER AIR BEFORE DRIVING
SOUTHWARD. ENSEMBLE SOLUTIONS EXHIBIT STANDARD DEVIATIONS THAT
FAVOR SIDING TOWARD THE MEANS...WHICH ARE MUCH COOLER THAN
OPERATIONAL SOLUTIONS. HAVE BLENDED IN HEAVIER WEIGHT TO ENSEMBLE
MEANS FOR SATURDAY.

IF ANY PERIOD OF THE LONGER RANGE WAS TO CONTAIN A PRECIPITATION
THREAT...IT WOULD LIKELY BE SATURDAY NIGHT ACROSS THE NORTHERN
CWA...AS SHARP MID LEVEL FRONT SLIPS SOUTHWARD AND ZONAL JET
ENTRANCE RIDES ALONG THE BOUNDARY.

OTHERWISE...REMAINDER OF THE PERIOD LOOKS DRY INTO EARLY NEXT
WEEK. COLDEST OF THE PERIOD WILL LIKELY BE SUNDAY INTO MONDAY AS
COLD SURFACE RIDGE EXPANDS THROUGH THE NORTHERN PLAINS...BUT
WITH UNCERTAINTY IN HOW MUCH IF ANY SNOW WILL SURVIVE THE MELT ON
FRIDAY...HAVE NOT GONE TOO EXTREME WITH COOLING UNDER RIDGE MONDAY
MORNING. AS STRONGLY AS CONDITIONS COOL...MOST GUIDANCE INDICATE
STRONG RIDGE BUILDING EARLY WEEK...WITH TEMPS ALOFT OUTPACING THE
WARMING AT LOW LEVELS. BY TUESDAY...STOUT SOUTHERLY SURFACE
GRADIENT MAY FINALLY ABLE TO DISPLACE THE COLD STABLE POOL...AND
TREND TOWARD EVEN WARMER IS WOULD SEEM TO BE IN THE CARDS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 511 PM CST TUE NOV 25 2014

LIGHT SNOW WILL SPREAD ACROSS THE AREA THROUGH THE
EVENING...POSSIBLY MIXED WITH RAIN THROUGH THE LOWER MISSOURI
RIVER CORRIDOR WHERE TEMPERATURES WILL INITIALLY BE WARMER. IFR
VISIBILITIES AND IFR/MVFR CEILINGS WILL OCCUR WITH THE SNOW.
NORTHWESTERLY WINDS WILL ALSO PICK UP LATER TONIGHT AND PERSIST
THROUGH WEDNESDAY...THOUGH BLOWING SNOW IS EXPECTED TO BE ONLY
PATCHY WITH SNOW ENDING BEFORE WINDS PICK UP.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON CST
     WEDNESDAY FOR MNZ071-072-080-081-090.

IA...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON CST
     WEDNESDAY FOR IAZ003.

NE...NONE.
&&

$$

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



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