Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 290327
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
927 PM CST SUN DEC 28 2014

.UPDATE...
ISSUED AT 925 PM CST SUN DEC 28 2014

GENERAL IDEA OF EARLIER FORECAST APPEARS TO BE ON THE RIGHT
TRACK...WITH ONLY MINOR ALTERATIONS REQUIRED. AREA OF SNOWFALL
STARTING TO DEVELOP DURING THE EVENING FROM CENTRAL SD INTO
EXTREME SOUTHEASTERN SD...WITH FEW FLURRIES EVEN STARTING AT KLRJ
AFTER 02Z...AND KFSD AROUND 03Z. AREA STARTING TO FEEL A BIT OF
WEAK PV ADVECTION...AND SLIGHT WARM AIR ADVECTION AT MID LEVELS...
AND MEAGER FRONTAL FORCING AND PV ADVECTION WILL PERSIST FOR
QUITE A WHILE TONIGHT AND MONDAY MORNING WITHIN MID LEVEL
CONFLUENCE...WITH FAVORED AREA GRADUALLY SLIPPING SOUTHWARD THE
LATTER PART OF THE NIGHT. THERMODYNAMIC PROFILES SOUTH OF I-90
LINE UP FAIRLY WELL LATER TONIGHT FOR SOME HEFTY SNOW TO LIQUID
RATIOS...PROBABLY 18-22/1 ON THE AVERAGE...WITH THE PEAK OF THE
WEAK LIFT ANCHORED IN DENDRITIC GROWTH ZONE.

WATCHING IMPACT OF VERY DRY AIR AT LOW LEVELS POISED TO THE
NORTH/NORTHEAST WHICH MAY IMPACT SNOW AMOUNTS SOMEWHAT NEGATIVELY
ON THE NORTH EDGE OF THE PRECIPITATION AREA...BOTH VIA INTERFERING
WITH ONSET...AND FROM DIMINISHING POTENTIAL SNOW-LIQUID RATIO.
TEMPS ALREADY INTO THE UPPER SINGLE DIGITS AT KATY AND KVVV WITH
DEW POINT CLOSING ON ZERO...AND WITH PERSISTENT NORTH TO NORTHEAST
WINDS...MAY NEED TO NUDGE TEMPS DOWN A COUPLE DEGREES. TO THE
SOUTH...THE LOWER CLOUDS AND PRECIPITATION WILL LIKELY LEAD TO A
NEARLY STEADY TEMPERATURE TRACE FOR A WHILE TONIGHT BEFORE
STARTING TO SLIP ON ADVECTION LATER ON IN THE NIGHT.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 255 PM CST SUN DEC 28 2014

MAIN FORECAST CONCERN THE NEXT 24 HOURS IS THE SNOW CHANCES AND THE
COMING ARCTIC AIRMASS. WATER VAPOR IMAGERY SHOWS JET HAS DUG INTO
COLORADO AND IS BEGINNING TO MOVE EAST NORTHEAST TOWARD NEBRASKA.
WHILE NO SNOW YET REPORTED IN SOUTH DAKOTA AND NEBRASKA...RADARS
SHOW A LOT OF VIRGA. EXPECT THAT AS THE WAVE CONTINUES TO MOVE
ENE...RADAR ECHOES WILL INCREASE IN COVERAGE AND SNOW WILL BEGIN TO
REACH THE GROUND BY LATE AFTERNOON.  AS THE WAVE CONTINUES TO MOVE
EAST TONIGHT...EXPECT A LARGE AREA OF LIGHT SNOW TO ORGANIZE ACROSS
NORTH CENTRAL NEBRASKA AND CENTRAL SD BETWEEN 00Z AND 06Z AND SPREAD
INTO SOUTHEAST SOUTH DAKOTA. THE SNOW IS NEVER GOING TO BE VERY
HEAVY GIVEN LACK OF ANY FRONTAL FORCING...BUT IT WILL BE A
PERSISTENT AREA OF LIGHT SNOW. EXPECT THAT SNOW WILL SPREAD AS FAR
NORTH AS I-90 DURING THE NIGHT WITH A FEW FLURRIES OR LIGHT
SNOW AS FAR NORTH AS HON AND BKX IN SD AND SLAYTON IN MN. SNOWFALL
WILL BE VERY EFFICIENT WITH 20:1 SNOW-LIQUID RATIOS EXPECTED. SO
DESPITE LIMITED MOISTURE...UP TO AN INCH OF SNOW MAY FALL NEAR I90
OVERNIGHT WITH 1 TO 2 INCHES NEAR THE MISSOURI RIVER IN SD. COLD
AIR WILL CONTINUE TO FUNNEL DOWN THROUGH THE NIGHT. MODELS ARE
BEGINNING TO HINT THAT COLD AIR MAY BE A BIT SLOWER IN ARRIVING
SOUTH OF I90 AND DID RAISE LOWS A BIT SOUTH OF I90 WITH LOWS FROM 5
TO 15 ABOVE.

LIGHT SNOW WILL CONTINUE IN THE MISSOURI VALLEY MONDAY MORNING BUT
SHOULD COME TO AN END BY MID MORNING ALONG I90.  THE SNOW WILL
CONTINUE TO SLOWLY MOVE SOUTH AS THE WAVE MOVES EAST OF THE AREA AND
COLD AIR CONTINUES TO ADVECT SOUTHWARD.  ANOTHER INCH OF SNOW IS
POSSIBLE IN THE MISSOURI VALLEY WITH ONLY A DUSTING TOWARD I90.
THERE COULD BE SOME DRIFTING SNOW AS NORTH WINDS OF 15 TO 20 MPH ARE
EXPECTED. TEMPERATURES ARE EXPECTED TO SLOWLY FALL THROUGH THE
DAY...WITH TEMPERATURES RANGING FROM AROUND ZERO NEAR HON AND MML
TO THE LOWER TEENS AROUND SUX AND SLB.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 255 PM CST SUN DEC 28 2014

ARCTIC HIGH PRESSURE SINKS SOUTHWARD ACROSS THE NORTHERN AND CENTRAL
HIGH PLAINS ON MONDAY NIGHT AND TUESDAY. SKIES WILL BECOME MOSTLY
CLEAR WITH THE EXCEPTION OF OUR FAR WESTERN AND SOUTHERN COUNTIES
WHERE SOME SCATTERED CLOUDS MAY LINGER INTO TUESDAY EVENING. WITH
NORTH NORTHWEST WINDS AROUND 10 MPH OR SO AND CLEARING
SKIES...TEMPERATURES WILL DROP SIGNIFICANTLY MONDAY NIGHT TO AROUND
10 BELOW ZERO...GIVE OR TAKE A FEW DEGREES...WITH SIMILAR READINGS
FRIGID CONDITIONS DO NOT IMPROVE MUCH ON TUESDAY AS THE HEART OF THE
COLD PLUNGE SETTLES INTO THE REGION. HIGHS WILL ONLY BE WITHIN A FEW
DEGREES OF ZERO. GIVEN THE CURRENT SNOWPACK AND STRENGTH OF THIS
COLD AIRMASS...WENT NEAR THE CONSMOS ON THE COLD SIDE OF GUIDANCE.
MAY NEED A WIND CHILL ADVISORY HEADLINE FOR MONDAY NIGHT AND TUESDAY
NIGHT WITH WIND CHILL READINGS AS COLD AS 20 TO 30 BELOW.

LOW LEVEL FLOW TURNS SOUTHWESTERLY TUESDAY NIGHT AND
WEDNESDAY...WITH SOME MODEST WARMING EXPECTED WEDNESDAY. HIGHS WILL
REACH THE TEENS ABOVE ZERO. WESTERLY FLOW ON WEDNESDAY NIGHT AND
THURSDAY WILL MODERATE TEMPERATURES FURTHER. LOWS WEDNESDAY NIGHT
WILL LIKELY OCCUR IN THE EVENING OR EARLY MORNING HOURS THEN REMAIN
STEADY OR RISE LATE AT NIGHT. HIGHS THURSDAY WILL REACH THE 20S.
CLOUDS BEGIN BUILDING BACK INTO THE REGION THURSDAY NIGHT AS A
CLIPPER WAVE MOVING ALONG THE NORTHERN STREAM DIVES ACROSS THE UPPER
MIDWEST. STILL SOME MODEL UNCERTAINTY IN HOW FAR SOUTH THE WAVE
DROPS. BUT WILL LEAVE IN SOME LOW CHANCE POPS MAINLY IN OUR
NORTHEAST ON FRIDAY AND FRIDAY NIGHT GIVEN THE MODEL UNCERTAINTY.
THE ARCTIC PUSH MAKES A COMEBACK NEXT WEEKEND BEHIND THE
TROUGH...ALTHOUGH THE MOST RECENT RUN OF THE ECMWF IS MUCH MORE
PROGRESSIVE...BRINGING SOME STRONGER WARMING INTO THE WESTERN PLAINS
ON SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 523 PM CST SUN DEC 28 2014

LIGHT SNOW WILL OVERSPREAD THE AREA TONIGHT...WITH THE HEAVIER
BAND LOCATED THROUGH THE MISSOURI RIVER CORRIDOR. VISIBILITIES
ARE EXPECTED TO REMAIN MOSTLY IN THE MVFR RANGE...WITH CEILINGS
DIPPING INTO THE IFR RANGE OR LOWER MVFR RANGE. IMPROVING
CONDITIONS AFTER 15Z ON MONDAY.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

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


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