Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 211752
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1152 AM CST SUN DEC 21 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 407 AM CST SUN DEC 21 2014

UPPER LEVEL ENERGY WITH THE NEXT SYSTEM TO AFFECT OUR AREA IS
CURRENTLY STREAMING THROUGH THE PACIFIC NORTHWEST VERY EARLY THIS
MORNING...BUT BEFORE THIS WE WILL HAVE TO CONTEND WITH THE STATUS
QUO OF LOW CLOUDS AND FOG THROUGHOUT MUCH OF TODAY. THE STRATUS DECK
WHICH LIES ACROSS THE MOST OF THE CWA THIS MORNING WILL FOR THE MOST
PART REMAIN ACROSS THE AREA...AND AREAS OF FOG...WITH LOCALLY DENSE
FOG...WILL SLOWLY IMPROVE BY LATE MORNING. OTHERWISE...WILL HAVE
SOME MODERATION IN TEMPERATURES TODAY IN AN INCREASING SOUTHERLY
FLOW OUT AHEAD OF THE NEXT SYSTEM...WITH HIGHS TOPPING OUT IN THE
MID 30S TO NEAR 40 FROM NORTH TO SOUTH. IT WILL ALSO BECOME BREEZY
IN OUR EAST WITH A TIGHTENING GRADIENT AND INCREASING MIXED LAYER
WINDS.

STILL SEEING SOME MODEL DIFFERENCES WITH TONIGHTS SYSTEM WITH THE
GFS AND NAM SHIFTING A LITTLE FARTHER TO THE SOUTH...WHILE THE ECMWF
TAKES THE SYSTEM A BIT FARTHER TO THE NORTH. BECAUSE OF THIS...THERE
ARE SOME DIFFERENCES IN TEMPERATURES ALOFT...WHICH MAY INFLUENCE
PRECIPITATION TYPE...THOUGH THAT MAY NOT REALLY HAVE THAT MUCH
IMPACT ANYWAY AS SURFACE TEMPERATURES LOOK TO REMAIN RELATIVELY MILD
THROUGHOUT TONIGHT...WITH ALMOST THE ENTIRE CWA REMAINING ABOVE
FREEZING ONCE PRECIPITATION BEGINS. NEWEST MODEL RUNS HAVE BEEN A
LITTLE MORE ROBUST WITH QPF AMOUNTS TONIGHT AS THE INITIAL PV
ANOMALY SWINGS THROUGH THE AREA...SO UPPED POPS INTO THE LIKELY
RANGE AS THE FEATURE LIFTS TO THE NORTH AND EAST. IT WILL REMAIN
BREEZY THROUGH MUCH OF THE AREA TONIGHT...AIDING IN KEEPING
TEMPERATURES UP...AND LOWS LOOK TO BE MAINLY MID AND UPPER 30S. IN
TERMS OF PRECIPITATION TYPE...THIS ALL PLAYS OUT TO MOSTLY RAIN
THROUGH THE SOUTHERN AND EASTERN PORTIONS OF THE CWA FOR ALMOST THE
ENTIRE NIGHT...WITH MIXED PRECIPITATION BEING CONFINED MAINLY TO THE
NORTHERN JAMES RIVER VALLEY INTO EAST CENTRAL SOUTH DAKOTA. EVEN
SO...ANY ICING LOOKS TO BE MINIMAL WITH THE RELATIVELY MILD SURFACE
TEMPERATURES...AND ANY SNOWFALL ACCUMULATION OVER THAT AREA SHOULD
REMAIN UNDER HALF AN INCH.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 407 AM CST SUN DEC 21 2014

TRICKY FORECAST IN THE MID RANGE AS THE MOST RECENT MODEL RUNS HAVE
ALL COME IN WITH A MORE SOUTHERN AND WESTERN TRACK WITH THE UPPER
LOW ON MONDAY. AS A RESULT...SURFACE AND LOW LEVEL TEMPERATURES ARE
A BIT COOLER ESPECIALLY ACROSS OUR WEST AND NORTH. WITH THE WARM
SECTOR RAINFALL IN OUR FAR EAST MONDAY MORNING PUSHING OUT OF THE
FORECAST AREA...MUCH OF THE AREA WILL BE IN THE DRY SLOT OF THE
STACKED LOW EARLY TO MIDDAY. TEMPERATURES WILL LARGELY BE AT OR JUST
ABOVE FREEZING DURING THIS TIME. PRECIPITATION CHANCES WILL REMAIN
ISOLATED TO SCATTERED THROUGH EARLY AFTERNOON AND VERY LIGHT. RAIN
AND SNOW WILL BE THE MAIN TYPE...WITH SOME SLEET OR FREEZING RAIN
EARLY IN THE DAY. NOT EXPECTING ANY ICING CONCERNS MONDAY WITH
MARGINAL TEMPERATURES...LIGHT PRECIPITATION AND A VERY SMALL WINDOW
OF OPPORTUNITY FOR FREEZING RAIN OR SLEET.

AS THE WRAP AROUND MOISTURE ADVANCES IN THE AFTERNOON AND COLDER AIR
BEGINS FILTERING IN FROM THE WEST...RAIN AND SNOW WILL SWITCH
ENTIRELY TO SNOWFALL LATE MONDAY AFTERNOON INTO THE EVENING. BROAD
AREA OF QG FORCING NEAR CENTRAL SD EARLY IN THE DAY SLIDES ACROSS
THE FORECAST AREA MONDAY NIGHT. MID LEVEL FRONTOGENESIS SETS UP NEAR
OUR WESTERN BORDER AND MOVES SLOWLY INTO SOUTHEAST SOUTH DAKOTA
OVERNIGHT AS IT BECOME LESS ORGANIZED. THE BEST POTENTIAL FOR LIGHT
TO MODERATE SNOWFALL WILL BE DURING THIS PERIOD MAINLY WEST OF A
BROOKINGS TO SALEM TO TYNDALL LINE...WITH LIGHTER SNOWFALL
ELSEWHERE. THE LOW SLOWLY EXITS THE REGION TUESDAY AND TUESDAY
NIGHT. LIGHT SNOWFALL WILL GRADUALLY TAPER OFF FROM WEST TO EAST
TUESDAY AFTERNOON AND EVENING. EXPECT 2 TO 4 INCHES IN THE
AFOREMENTIONED AREA AND LESS THAN AN INCH AND A HALF ELSEWHERE.
SIOUX FALLS AND SIOUX CITY LOOK TO BE AROUND 1 INCH. WINDS LOOK TO
INCREASE TO 15 TO 30 MPH ACROSS OUR WEST ON MONDAY NIGHT AND
TUESDAY...SO ADDED SOME PATCHY BLOWING SNOW MENTION. AS MENTIONED
PREVIOUSLY HOWEVER...WITH MODELS HAVING A TENDENCY TO FLIP FLOP WITH
EACH RUN...COULD SEE THIS SCENARIO CHANGE IF THINGS TREND BACK NORTH
OR FURTHER EAST AGAIN. UPCOMING SHIFTS MAY NEED TO LOOK INTO THE
POSSIBILITY OF A WINTER WEATHER ADVISORY IN OUR WEST IF BLOWING SNOW
AND DECENT SNOW AMOUNTS CONTINUE TO BE A CONCERN.

NORTHWEST UPPER FLOW WEDNESDAY AND WEDNESDAY NIGHT BECOMES MORE
ZONAL ON CHRISTMAS DAY AHEAD OF THE NEXT UPPER SHORTWAVE. PARTLY TO
MOSTLY CLOUDY SKIES ARE EXPECTED WITH NEAR SEASONAL TEMPERATURES IN
THE MID 20S AND LOWER 30S WEDNESDAY AND THURSDAY. MODELS SHOWING
MUCH BETTER AGREEMENT IN THE TIMING AND TRACK OF THE SHORTWAVE
DROPPING ACROSS THE REGION. A BAND OF LIGHT TO MODERATE SNOWFALL
WILL SINK SOUTHEASTWARD THROUGH THE CWA THURSDAY AND THURSDAY NIGHT.
DID GO AHEAD AND BOOST POPS 10 TO 20 PERCENT ACROSS OUR CENTRAL AND
SOUTHERN TWO THIRDS DURING THIS PERIOD. COOLER AIR ARRIVES IN ITS
WAKE ON FRIDAY AND SATURDAY WITH HIGHS ONLY IN THE UPPER TEENS TO
MID 20S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1146 AM CST SUN DEC 21 2014

LIFR TO IFR CIGS AND VIS CONTINUE OVER A GOOD PORTION OF THE AREA.
CLEARING STARTING TO MAKE PROGRESS EAST...CURRENTLY NEAR THE
JAMES RIVER. THIS CLEARING COULD MAKE IT AS FAR EAST AS KHON OR
KFSD...SO WILL CONTINUE TO MONITOR TRENDS. FOR NOW WILL KEEP THE
TAFS PESSIMISTIC AS STILL THINK THAT IS THE MORE LIKELY SOLUTION.
WILL SEE RAIN DEVELOP LATER TONIGHT...POSSIBLY MIXED WITH SOME
SLEET. CIGS COULD BUMP UP INTO IFR OR LOW END MVFR AFTER THE RAIN
STARTS...AND VIS SHOULD NOT BE AS BAD AS THIS MORNING. RAIN WILL
SLOWLY TRANSITION TO SNOW...BUT THINK AREAS EAST OF THE JAMES
RIVER WILL PROBABLY BE PREDOMINATELY RAIN THROUGH 18Z.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR SDZ038>040-053>056-
     059>062-065>067.

MN...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR MNZ071-080-089-097-
     098.

IA...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR IAZ001-002-012.

NE...NONE.
&&

$$

SHORT TERM...JM
LONG TERM...
AVIATION...CHENARD



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