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000
FXUS63 KFSD 040347
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
947 PM CST TUE DEC 3 2013

.UPDATE...
ISSUED AT 945 PM CST TUE DEC 3 2013

MODELS CONTINUE TO HAVE DIFFICULTY WITH THE EVOLUTION OF TONIGHTS
SYSTEM. A LOT OF ENERGY DIVING SOUTHEAST INTO THE TROUGH...AND JUST HOW
MUCH AND WHEN THIS FORCING EJECTS EAST IS THE ISSUE. HRRR AND RAP
HAVE BEEN INCONSISTENT FROM RUN TO RUN AND THUS NOT OF MUCH USE WITH
THIS SYSTEM. RADAR TRENDS SHOW AN EXPANDING AREA OF MAINLY LIGHT SNOW
ALONG AND JUST SOUTH OF INTERSTATE 90...WITH AN EXPANDING AREA OF
MODERATE TO AT TIMES HEAVY SNOW IN NORTH CENTRAL NEBRASKA AND SOUTH
CENTRAL SOUTH DAKOTA. ACTIVITY SEEMS TO NOW BE EXPANDING NEAR THE 700
MB FRONT IN AN AREA OF BROAD ISENTROPIC LIFT AND INCREASING PV
ADVECTION. FRONTOGENESIS NOT AS WELL DEFINED IN LATEST MODEL
RUNS...SUGGESTING WE END UP SEEING A BIT OF A BROADER AREA OF
MODERATE SNOW. BASED ON RADAR TRENDS AND THE LATEST 0Z NAM...SEEMS
LIKE THIS AREA OF SNOW WILL TRACK A BIT NORTHWEST OF THE PREVIOUS
FORECAST...BUT NOT BY MUCH. AND BY AFTER MIDNIGHT...WOULD EXPECT THAT
LATTER AREA OF STEADY SNOW THAT IS CURRENTLY MOVING NORTHEAST...TO
BE FORCED MORE EASTERLY BY THE APPROACHING PV ANOMALY. THIS SHOULD
BRING THIS AREA OF SNOW THROUGH ALL THE COUNTIES CURRENTLY IN THE
HEADLINE. DID ADJUST POPS UPWARD IN THE MORNING TO ACCOUNT FOR THIS
SLOWER TIMING. ALSO WE STAY SATURATED THROUGH THE DAY...AND AS ONE
MORE PUSH OF LIFT MOVES ACROSS DURING THE LATE MORNING AND EARLY
AFTERNOON WE MAY VERY WELL SEE ANOTHER LITTLE BURST OF SNOW DROPPING
ANOTHER INCH OR SO...SORT OF LIKE THE 0Z NAM SHOWS.

STILL LOOKS LIKE A WIDESPREAD 3 TO 6 INCHES IN THE WARNING...WITH
ISOLATED HIGHER AMOUNTS AROUND 7 INCHES...ESPECIALLY IF RATIOS END
UP A BIT HIGHER OR IF WE DO SEE A BIT MORE ENHANCED BANDING. LATEST
TRENDS WOULD SUGGEST THE BEST CHANCE OF SEEING THESE HIGHER AMOUNTS
WILL BE FROM GREGORY TO MITCHELL TO MARHSALL...WITH AMOUNTS ON THE
LOWER SIDE OF THE RANGE AS YOU GET TO THE SOUTHEAST EDGE OF THE
WARNING. HEADLINES LOOK IN GOOD SHAPE...AND THUS NO CHANGES PLANNED.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 350 PM CST TUE DEC 3 2013

RELATIVE QUIET PERIOD FROM LATE MORNING INTO EARLY AFTERNOON IS
STARTING TO CHANGE AS LIFT FORCING SPREADS INTO SOUTH CENTRAL SOUTH
DAKOTA IN ADVANCE OF STRONG JET PUNCHING OUT OF THE CENTRAL ROCKIES.
STRONG FRONTOGENETIC FORCING WILL CONTINUE TO EXPAND ENE ALONG MID
LEVEL BOUNDARY THROUGH THE EVENING...AND SHOULD LEAD TO A QUICK
DEVELOPMENT OF SNOW BAND WITH LIFT AND SNOW GROWTH WELL COLLOCATED
IN PROFILES OF MAIN BAND. SHADED TOWARD A SOMEWHAT COOLER THERMAL
PROFILE OVERALL WITH WET BULB EFFECT AND SUPPORT OF EC/SREF. EVEN
WITH THIS...SHOULD BE WARM ENOUGH ALOFT FOR SOME ALTERNATE TYPES IN
TRANSITION AT ONSET...PROBABLY SLEET AND LIGHT FREEZING RAIN BEFORE
A CHANGE TO SNOW. SOME LIGHT ICE ACCUMULATIONS MENTIONED FOR AREAS
AROUND THE IOWA GREAT LAKES...WHERE LOW LEVEL COOL PUSH WILL BE IN
PROXIMITY TO THE LINGERING WARMER AIR ALOFT.

MAIN CHANGE IN THE FORECAST FROM THE MID TO LATE MORNING UPDATE WAS
TO INTRODUCE A WINTER STORM WARNING TO AREAS GENERALLY NORTH OF A
WINDOM TO SIOUX FALLS TO WAGNER LINE. STILL LOOKING AT A BROAD
BANDING OF 4 TO 6 INCHES SNOWFALL...WITH LOCALLY HEAVIER AMOUNTS.
HARD TO PINPOINT THE EXACT LOCATION OF THE HEAVIER BAND...THE
STRONGER REASON FOR UPGRADING TO THE WARNING WAS COMBINING THE
SNOWFALL WITH GUSTY WINDS OF 25 TO 35 MPH. STRONGEST WINDS WILL
FIRST DEVELOP ACROSS THE WESTERN CWA AFTER MIDNIGHT...AND EXPAND
EASTWARD AS LOW PRESSURE INTENSIFIES TO THE SOUTHEAST LATER TONIGHT
AND WEDNESDAY. WINDS WILL BE SLOW TO INCREASE IN THE FAR EAST WITH
BAGGY GRADIENT NEAR THE INVERTED TROUGH...BUT EVENTUALLY WILL
INCREASE AND CREATE PROBLEMS WITH STRONGER GRADIENT BY LATE DAY IN
SW MN. BLOWING SNOW SHOULD REDUCE VISIBILITIES TO AROUND A HALF MILE
AT TIMES...AND COULD BE BRIEFLY LOWER AT TIMES OF FALLING SNOW.

SNOWFALL NOW LOOKING A BIT MORE APT TO CONTINUE INTO WEDNESDAY
ACROSS THE AREA...BUT WILL SLOW UP FROM SOUTHWEST TO NORTHEAST AS
INVERTED TROUGH PULLS EAST...AND UPPER WAVE WANDERS SLOWLY NORTH OF
THE AREA. TEMPERATURES WILL BE IN STRONG SUPPORT OF ICE PROCESSES
DURING THE DAY...SO PERHAPS EVEN FAVORABLE FOR FLURRIES AFTER
MEASURABLE THREAT WANES.

OTHERWISE...SOME AREAS OF DENSE FOG CONTINUE THIS AFTERNOON ACROSS
SOUTHWEST MINNESOTA...AND SO NOT TO CONFUSE WITH OVERALL WINTER
SCENARIO...HAVE NOT ISSUED A SEPARATE ADVISORY ON THIS FEATURE.
THERE WILL LIKELY BE SOME PATCHES OF FREEZING DRIZZLE INTERSPERSED
WITH FLURRIES UNTIL STRONGER FORCING AND DEEPER MOISTURE SPREADS IN
BY THE EVENING.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 350 PM CST TUE DEC 3 2013

ANY LIGHT SNOW WILL TAPER DOWN TO FLURRIES ON WEDNESDAY NIGHT AS THE
SYSTEM PULLS AWAY AND FORCING IS LOST. CONFINED ANY BLOWING SNOW IN
THE EVENING TO AREAS WHICH COULD ACTUALLY RECEIVE AT LEAST A TENTH
OF AN INCH OF SNOW...THOUGH WINDS WILL ONLY MARGINALLY DIMINISH
OVERNIGHT WITH A TIGHT GRADIENT REMAINING ACROSS THE REGION...SO
COULD SEE PATCHY BLOWING SNOW OVER OTHER AREAS. EVEN WITH COLD AIR
ADVECTION CONTINUING...TEMPERATURES WILL REMAIN SOMEWHAT IN CHECK ON
WEDNESDAY NIGHT WITH ABUNDANT CLOUD COVER AND THE ABOVE MENTIONED
WINDS...THOUGH READINGS WILL STILL DROP TO AROUND ZERO BY VERY EARLY
THURSDAY MORNING. WIND CHILLS OVERNIGHT WILL JUST MEET WIND CHILL
CRITERIA IN SOME AREAS...AND MAY HAVE TO DEAL WITH THAT AT SOME
POINT IN REGARD TO HEADLINES...BUT WITH THE CURRENT HEADLINES OUT
DID NOT WANT TO CONFUSE THE MATTER.

SURFACE HIGH PRESSURE BEGINS TO BUILD INTO THE REGION ON
THURSDAY...AND IT WILL REMAIN BREEZY IN A COLD AIR ADVECTION
REGIME...ALTHOUGH WINDS WILL SLOWLY TAPERING DOWN DURING THE DAY AS
THE GRADIENT RELAXES A BIT. NOT SURE HOW QUICKLY CLOUDS WILL
DECREASE DURING THE DAY...WITH BOTH THE NAM AND GFS HINTING AT
STRATUS LINGERING THROUGH THE DAY. IN LIGHT OF THAT AND WITH SNOW
COVER ACROSS THE AREA WENT ON THE LOW SIDE OF GUIDANCE WITH HIGHS
ONLY IN THE SINGLE DIGITS AND TEENS. BY THURSDAY NIGHT IT DOES LOOK
LIKE THERE SHOULD BE MORE CLEARING...THOUGH WINDS WILL NOT
COMPLETELY DROP OFF...REMAINING CLOSE TO 10 KTS. BECAUSE OF
THAT...AGAIN THINK THAT TEMPERATURES WILL NOT COMPLETELY BOTTOM
OUT...THOUGH WENT ON THE LOW SIDE OF GUIDANCE WITH LOWS FROM NEAR 10
BELOW IN THE NORTH TO NEAR ZERO IN THE FAR SOUTHEAST. IF WINDS WOULD
BECOME CALM THEN IT WILL BE COLDER THAN CURRENTLY FORECASTED.

BY FRIDAY...925 MB TEMPERATURES ARE PROGGED TO BE WELL INTO THE
NEGATIVE UPPER TEENS TO NEGATIVE LOWER 20S C...AND WENT BELOW
GUIDANCE WITH HIGHS IN THE SINGLE DIGITS. FRIDAY NIGHT IS SETTING UP
TO BE THE COLDEST NIGHT OF THE NEXT FEW AS THE HIGH PRESSURE AXIS
MOVES OVERHEAD AND WINDS BECOME NEARLY CALM. THE ONLY FLY IN THE
OINTMENT WILL BE THE POSSIBILITY OF INCREASING MID AND HIGH
CLOUDS...BUT WENT BELOW ALL BLEND GUIDANCE...AND AM STILL PROBABLY
TOO WARM AS MODEL RUNS ARE COLDER. AT THIS POINT...HAVE LOWS IN THE
MID TEENS BELOW ZERO TO THE SINGLE DIGITS BELOW.

IN THE EXTENDED...SATURDAY THROUGH TUESDAY...THE COLD AIR LOOKS TO
BE LOCKED IN THROUGH THE PERIOD. MODELS IN FAIRLY DECENT AGREEMENT
ON BRINGING A CHANCE OF SNOW TO THE AREA SOMETIME IN THE SUNDAY TIME
FRAME...AS A NORTHERN STREAM UPPER LEVEL TROUGH BEGINS TO DROP INTO
THE NORTHERN PLAINS AND A SOUTHERN STREAM WAVE EJECTS OUT OF THE
DESERT SOUTHWEST. A REINFORCING SHOT OF COLD AIR DROPS INTO THE
REGION FOR THE BEGINNING OF NEXT WEEK WITH THE PASSAGE OF THIS
SYSTEM...AND MODELS HINTING THAT IT COULD BE EVEN COLDER THAN THE
UPCOMING COLD SPELL...THOUGH WILL HAVE TO WATCH AS IT IS STILL
PRETTY FAR OUT. IN ANY EVENT...STAYED ON THE LOW SIDE OF GUIDANCE
THROUGH THE PERIOD WITH EXPECTED SNOW COVER. THIS WILL PLAY OUT TO
HIGHS SINGLE DIGITS AND TEENS AND LOWS A FEW DEGREES EITHER SIDE OF
ZERO.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 555 PM CST TUE DEC 3 2013

COMPLEX WEATHER PATTERN SETTING UP ACROSS THE AREA THROUGH THE TAF
PERIOD WITH LOW CEILINGS AND VISIBILITY EXPECTED. CEILINGS WILL
LARGELY BE IFR-LIFR WITH VISIBILITY LIKEWISE DROPPING INTO THE IFR
RANGE AS SNOW EXPANDS ACROSS THE REGION. HEAVIER BAND OF SNOW WILL
RESULT IN LIFR VISIBILITY AT TIMES...AND WHILE EXACT LOCATION OF THE
HEAVIER BAND IS DIFFICULT TO PINPOINT...THE BEST POTENTIAL APPEARS
TO BE FROM SOUTH CENTRAL SD THROUGH KFSD INTO THE KMWM/KMML AREAS IN
SOUTHWEST MN. FAR SOUTHEAST SD AND MOST OF NORTHWEST IOWA WILL SEE
LESSER CHANCES OF PRECIPITATION...THOUGH IFR-LIFR CEILINGS STILL
EXPECTED. IN ADDITION TO FALLING SNOW...INCREASING NORTH-NORTHWEST
WINDS THROUGH THE PERIOD WILL RESULT IN FURTHER REDUCED VISIBILITY
IN BLOWING SNOW AT TIMES.

CONDITIONS WILL IMPROVE GRADUALLY FROM SOUTHWEST TO NORTHEAST AFTER
09Z-12Z...THOUGH EXPECT MVFR CONDITIONS AT BEST...AS SCATTERED LIGHT
SNOW AND AREAS OF BLOWING SNOW CONTINUE.


&&

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

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

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

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

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

NE...NONE.
&&

$$

UPDATE...CHENARD
SHORT TERM...CHAPMAN
LONG TERM...JM
AVIATION...JH