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000
FXUS63 KFSD 010458
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1058 PM CST FRI FEB 28 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 352 PM CST FRI FEB 28 2014

LIGHT TO MODERATE SNOW CONTINUES TO MOVE ACROSS SOUTHWEST MINNESOTA
AND NORTHWEST IOWA THIS AFTERNOON. INTENSITY HAS INCREASED SOME AS
EXPECTED...AS THE APPROACHING PV ANOMALY INTERACTS WITH THE MID
LEVEL FRONTAL BOUNDARY OVERHEAD. GENERALLY LOOKING AT UP TO AN INCH
OR TWO OF ACCUMULATION FROM EXTREME SOUTHEAST SOUTH DAKOTA EAST INTO
NORTHWEST IOWA AND THE SOUTHERN PORTION OF SOUTHWEST MINNESOTA.
STILL EXPECT THIS SNOW TO EXIT NORTHWEST IOWA BY AROUND 7 PM.
ATTENTION WILL THEN TURN TO OUR NEXT SYSTEM COMING IN FROM THE WEST.
ISENTROPIC LIFT INCREASES LATE TONIGHT INTO EARLY TOMORROW AS WARM
MOIST AIR OVERRIDES THE LOW LEVEL COLD DOME SINKING SOUTH FROM THE
BUILDING ARCTIC HIGH PRESSURE SYSTEM. LIFT AHEAD OF AN APPROACHING
PV ANOMALY DURING THE AFTERNOON WILL ALLOW THE LIGHT SNOW TO LINGER
FOR MUCH OF THE DAY. MODELS COMING INTO PRETTY GOOD AGREEMENT WITH
THIS SYSTEM...WITH THE HIGHEST QPF SOUTH OF INTERSTATE 90. THIS MAKES
SENSE...AS THIS WILL BE WHERE THE STRONGEST THERMAL GRADIENT IS AND
THE DRY LOW LEVELS TO THE NORTH WILL LIMIT THE NORTHWARD EXTENT OF
HIGHER AMOUNTS. THUS A BLEND OF THE GFS...NAM...ECMWF AND ARW SEEMED
LIKE A GOOD STARTING POINT FOR QPF. TIMING BRINGS THE SNOW INTO
SOUTH CENTRAL SOUTH DAKOTA AFTER MIDNIGHT...APPROACHING INTERSTATE
29 AROUND 6 AM...AND OUR FAR EAST AROUND 9 AM.

GIVEN THE GOOD MODEL AGREEMENT...SNOWFALL AMOUNT UNCERTAINTY IS
MAINLY ASSOCIATED WITH RATIO UNCERTAINTY. DENDRITIC LAYER IS PRETTY
DEEP SUGGESTING HIGHER RATIOS. HOWEVER THE MAXIMUM LIFT IS PRETTY
HIGH IN THE PROFILE...ABOVE THE LOW LEVEL COLD DOME. THUS THE SNOW
WILL HAVE TO DESCEND THROUGH A PRETTY DEEP LAYER OF WIND SHEAR AND
SUBSIDENCE. THIS COMBINED WITH THE LOW LEVEL DRY AIR ADVECTION
SHOULD HELP KEEP RATIOS IN CHECK. SO FOR NOW WILL GENERALLY GO
CLOSE TO 15 TO 1. THIS RESULTS IN 3 TO 5 INCHES ALONG THE MISSOURI
RIVER CORRIDOR...1 TO 3 INCHES FROM HURON TO SIOUX FALLS TO SPENCER
IOWA...AND AND UP TO AN INCH OR TWO NORTHEAST OF THERE. AGAIN IF
RATIOS END UP A BIT HIGHER THEN AMOUNTS WOULD BE TOO...SO NOT OUT OF
THE QUESTION THAT WE SEE A FEW 6 INCH AMOUNTS NEAR THE MISSOURI
RIVER...BUT FEEL THIS IS A LOWER PROBABILITY EVENT AT THIS TIME.

TEMPERATURES TONIGHT WILL STEADILY FALL AS COLD AIR PUSHES SOUTH.
TEMPERATURES TOMORROW WILL BE NEARLY STEADY...OR EVEN SLOWLY FALL
THROUGH THE DAY...WITH READINGS AT OR BELOW ZERO OVER MOST OF THE
CWA. THIS COMBINED WITH A NORTHERLY BREEZE OF 10 TO 20 MPH WILL
RESULT IN WIND CHILLS OF 20 TO 25 BELOW ZERO FOR MOST OF THE DAY.
DECIDED TO ISSUE A WINTER WEATHER ADVISORY FOR THE MISSOURI RIVER
CORRIDOR WHERE AMOUNTS WILL BE HIGHEST. ALSO WILL HAVE A WIND CHILL
ADVISORY FOR THE WHOLE CWA.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 352 PM CST FRI FEB 28 2014

EVEN THOUGH BEST OF UPPER LEVEL FORCING WILL START TO EXIT FAIRLY
RAPIDLY...AND SNOWFALL WITH INCREASING HIGHER AND HIGHER LIFT IN
THE FRONTAL ZONE WILL BE WHITTLED AWAY BY PERSISTENT DRY AIR
ADVECTION FROM THE NORTH...TEMPS AND MOISTURE WOULD SHOW A
PREFERENCE TO KEEP SOME FAIRLY HIGH LEVEL POPS GOING ACROSS THE
FAR SOUTH INTO THE EARLY EVENING...WHILE TRENDING DOWN QUICKLY
FROM NORTH TO SOUTH. CONTINUED WINTER WEATHER ADVISORY IN THE
SOUTHEAST THROUGH 03Z...ENDING WITH MORE LIKELY DEMISE OF THE MORE
WIDESPREAD LIGHT SNOW THREAT. OTHERWISE...STORY FOR THE REMAINDER
OF THE NIGHT...AND ON THROUGH MONDAY...WILL BE THE UNPRECEDENTED
CHILL. FIRST TWO OR THREE DAYS OF MARCH WILL LIKELY RANK AS THE
COLDEST START TO THE MONTH...AND FAIRLY SOLID CHANCE AT A FEW
RECORD LOWS AND RECORD COLD MAXIMA. WILL HAVE TO SEE IF CAN MAKE A
RUN AT THE MARCH TEMPERATURES OF ALL TIME AT KFSD -23 (3/11/48)
AND KSUX -22 (3/5/1960). COLDEST FOR MOST SHOULD BE MONDAY MORNING
WITH WINDS MORE FULLY DIMINISHED...AND MAINLY CLEAR SKIES OTHER
THAN THREAT FOR A FEW HIGH CLOUDS. AIR MASS DOES SHAKE OUT A BIT
COLDER ON SUNDAY MORNING...BUT EXPECT WILL AT LEAST HAVE A FAIR
AMOUNT OF MID TO HIGH CLOUDS REMAINING ALONG WITH A BETTER
NORTHERLY GRADIENT. PERSISTENT NORTHERLY WINDS WILL BRING CHILL
TO THE FOREFRONT AFTER THE SNOW EXITS SATURDAY NIGHT...AND HAVE
MAINTAINED THE WIND CHILL ADVISORY INTO SUNDAY. WHILE DID NOT MAKE
ANY CHANGES AT THIS TIME...IT IS FAIRLY LIKELY THAT MAY END UP
WITH A LIMITED AREA WITH WIND CHILL WARNINGS FOR LATER SATURDAY
NIGHT INTO SUNDAY MORNING...AND EVEN AGAIN ON SUNDAY NIGHT INTO
MONDAY MORNING. ALL IN ALL...EITHER LAMB OR LION...IT WILL BE A
FROZEN ONE TO WELCOME THE MONTH.

SUNDAY WILL LIKELY FIND MORE AREAS STRUGGLING TO GET ABOVE ZERO
WITH THE CONTINUED COLD AIR ADVECTION...AND EVEN MONDAY NOT MUCH
OF A PICNIC FOR TEMPS AS WILL BE TRAJECTORIED OUT OF THE COLD
RIDGE EVEN IN THE WEST. WILL HAVE A SHOT AT QUICK DROP IN THE EAST
ON MONDAY NIGHT WITH LINGERING EDGE OF RIDGE AXIS...BUT THEN WILL
START TO SEE MORE CLOUDS AND A STRENGTHENING RETURN FLOW.

FOR THE REMAINDER OF THE EXTENDED RANGE FROM TUESDAY THROUGH
FRIDAY...SHOULD ACTUALLY FIND SOME FAIRLY DISTINCT MODERATION TO
TEMPERATURES AS CONFLUENCE WEAKENS AND SHIFTS EASTWARD WITH MORE
OF A NORTHWEST FLOW AS RIDGING SHIFTS EASTWARD TOWARD THE FAR
WESTERN PLAINS. UNFORTUNATELY...THIS AGAIN PUTS THE AREA IN MORE
OF A CLIPPER FLOW WITH VERY ILLY TIMED WAVES. AS NO WAVES WILL
LIKELY DIG ENOUGH TO RETAIN COLD AIR...AND IN FACT THERE IS A
STRONG CONSENSUS THAT WAVE ON THURSDAY WILL PUT AREA INTO A STRONG
WARM SECTOR AS IT PASSES WELL NORTH OF THE CWA. AT THIS POINT...
APPEARS TO BE THE FIRST ABOVE NORMAL DAY FOR THE AREA IN ALMOST
TWO WEEKS. ALMOST EVERY PERIOD LITTERED WITH A SLIGHT CHANCE POP
BECAUSE OF THE RANDOMLY TIMED WAVES...AND HAVE TRIED TO TRIM A FEW
PERIODS TO BE MORE IN LINE WITH THE ECMWF TIMING WHICH HAS BEEN
MORE CONSISTENT RUN TO RUN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1054 PM CST FRI FEB 28 2014

PATCHY MVFR STRATUS BEHIND AN EXITING SNOW BAND IS EXPECTED TO
CONTINUE TO DECREASE EARLY THIS MORNING WITH MAINLY MID AND HIGH
CLOUDS LINGERING EXPECTED. THE NEXT WAVE OF SNOWFALL WILL SLOWLY
SPREAD WEST TO EAST BEGINNING AROUND 08Z IN SOUTH CENTRAL
SD...REACHING THE I29 CORRIDOR AROUND DAYBREAK AND OUR EASTERN
FORECAST AREA BORDER BY AROUND 16Z. OCCASIONAL LIGHT TO MODERATE SNOW
WILL PERSIST THROUGH THE REMAINDER OF THE TAF PERIOD...THEN BEGIN TO
TAPER OFF FROM NORTHWEST TO SOUTHEAST BEGINNING IN SOUTH CENTRAL
AROUND 22Z AND THE FAR SOUTHEAST BY 06Z/SUNDAY. EXPECT MVFR
CEILINGS...WITH VISIBILITY IN THE MVFR AND IFR CATEGORY. COULD EVEN
SEE A VERY BRIEF PERIOD OF LIFR NEAR THE MISSOURI VALLEY - INCLUDING
KSUX IN THE MID TO LATE MORNING HOURS. WINDS WILL GENERALLY BE AROUND
10 TO 20 KT...SO AM NOT EXPECTING SIGNIFICANT BLOWING SNOW
CONDITIONS.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY FROM 6 AM TO 9 PM CST SATURDAY FOR
     SDZ070-071.

     WIND CHILL ADVISORY FROM 3 AM SATURDAY TO NOON CST SUNDAY FOR
     SDZ038>040-052>062-064>067.

     WIND CHILL ADVISORY FROM 6 AM SATURDAY TO NOON CST SUNDAY FOR
     SDZ050-063-068>071.

     WINTER WEATHER ADVISORY UNTIL 6 PM CST SATURDAY FOR SDZ050-057-
     063-068-069.

MN...WIND CHILL ADVISORY FROM 3 AM SATURDAY TO NOON CST SUNDAY FOR
     MNZ071-072-080-081-089-090-097-098.

IA...WINTER WEATHER ADVISORY FROM 6 AM TO 9 PM CST SATURDAY FOR
     IAZ020>022-031-032.

     WIND CHILL ADVISORY FROM 3 AM SATURDAY TO NOON CST SUNDAY FOR
     IAZ001>003-012>014-021-022.

     WIND CHILL ADVISORY FROM 6 AM SATURDAY TO NOON CST SUNDAY FOR
     IAZ020-031-032.

NE...WINTER WEATHER ADVISORY FROM 6 AM TO 9 PM CST SATURDAY FOR
     NEZ013-014.

     WIND CHILL ADVISORY FROM 6 AM SATURDAY TO NOON CST SUNDAY FOR
     NEZ013-014.

&&

$$

SHORT TERM...CHENARD
LONG TERM...CHAPMAN
AVIATION...