000
FXUS63 KFSD 031019
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1115 PM CST MON DEC 2 2013

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 340 PM CST MON DEC 2 2013

MODELS STARTING TO COME INTO BETTER AGREEMENT ON STORM SYSTEM MOVING
THROUGH THE MIDWEST THOUGH THERE ARE SOME FAIRLY SIGNIFICANT
DIFFERENCES AMONGST THE VARIOUS SOLUTIONS.  WITH
COLABORATION...OPTED TO SIDE WITH A EC/GEM BLEND...WHICH GIVES SOME
OF THE HIGHER SNOW TOTALS FOR OUR FORECAST AREA.

IN THE IMMEDIATE TERM...HAVE A BAND OF FOG THAT HAS DEVELOPED AND IS
GRADUALLY WORKING SOUTH THROUGH THE FORECAST AREA.  ON THE LEADING
EDGE OF THE BAND...VISIBILITIES DROP DOWN TO A QUARTER OF A MILE OR
SO...THEN SEEM TO SETTLE IN THE 1-4 MILES RANGE BEHIND THE INITIAL
PUSH.  ACROSS SOUTHWEST MINNESOTA...VISIBILITIES ARE LOWER...AND
WITH NORTHEAST FLOW REMAINING THROUGH THE MORNING HOURS...EXPECT
MOISTURE TO BECOME TRAPPED ALONG THE EASTERN EDGE OF THE BUFFALO
RIDGE.  HAVE ISSUED A DENSE FOG ADVISORY ALONG AND EAST OF THE
BUFFALO RIDGE...THOUGH ADVISORY MAY NOT RUN LONG ENOUGH IN TIME AS
FOG SHOULD BE RELATIVELY SLOW TO ABATE TODAY.

FOR TODAY...ISENTROPIC LIFT EXPECTED TO INCREASE FROM WEST TO EAST
ACROSS THE FORECAST AREA.  INITIALLY...THERE IS A WARM BUT
UNSATURATED LAYER FROM 900-800MB.  WITH SURFACE TEMPERATURES BELOW
FREEZING...COULD SEE SOME LIGHT FREEZING RAIN IF PRECIPITATION
DOESN/T EVAPORATE BEFORE REACHING THE SURFACE.  ONCE PRECIPITATION
INTENSITY INCREASES...EXPECT WARM LAYER TO WET BULB DOWN TO NEAR OR
SUB FREEZING PROFILE RELATIVELY QUICKLY.  EXPECT SNOW TO DEVELOP
ACROSS THE NORTHWERN AND WESTERN PORTIONS OF THE FORECAST AREA
THROUGH THE AFTERNOON HOURS...GRADUALLY SHIFTING SLOWLY SOUTH AS
LIFT INCREASES AND OVERCOMES THE DRY AIR.

TONIGHT...MODELS ARE ALL SHOWING A STRONG AREA OF MID LEVEL
FRONTOGENESIS NEAR 700 MB DEVELOPING FROM NEAR TYNDYLL/LAKE
ANDES-MARSHALL MINNESOTA.  WITH MUCH STRONGER COLD AIR ADVECTION
THROUGH THE OVERNIGHT HOURS AND PRESSURE GRADIENT TIGHTENING...COULD
SEE SOME AREAS OF BLOWING SNOW DEVELOPING ESPECIALLY AFTER 06Z. SNOW
RATIOS WILL VARY WIDELY ACROSS THE FORECAST AREA...WITH WARM MILD
AIRMASS ACROSS NORTHWEST IOWA LEADING TO SNOW RATIOS OF
8-10:1...WHILE FURTHER TO THE WEST IN THE ARCTIC AIR SNOW RAITOS
WILL APPROACH 20:1.  THIS SNOW WILL BE QUITE PROBLEMATIC ESPECIALLY
WITH STRONG NORTHWEST WINDS OF 20-30 MPH DEVELOPING.  WENT AHEAD AND
ISSUED A WINTER WEATHER ADVISORY FOR WEST AND NORTH WHERE SNOW
ACCUMULATIONS OF TWO TO FOUR INCHES OF SNOW IN COMBINATION WITH
STRONG NORTHWEST WINDS WILL HAMPER TRAVEL.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 340 PM CST MON DEC 2 2013

ACCORDING TO ALL MODEL GUIDANCE EXCEPT THE EC...UPPER SUPPORT FOR
THE STEADIEST SNOW NEAR THE NORTHERN EDGE OF OUR FORECAST AREA WILL
BE PULLING OUT TUESDAY EVENING. THE NCEP MODELS PROBABLY PULL A
LITTLE TOO MUCH OUT WITH INITIAL OVERDONE WAVE...AND A FAVORABLE
PATTERN FOR AREAS OF LOWER LEVEL LIGHT SNOW SEEMS TO EXIST...SO
WILL START WITH 50 OR SO POPS IN OUR NORTHEAST TUESDAY
EVENING...WELL MATCHING TUESDAY AFTERNOON...AND SLOWLY DECREASING
DURING TUESDAY NIGHT. THE EC AND GFS AND GEM HAVE ALL BEEN
KICKING OUT TOO MUCH PRECIPITATION LATELY...LAST NIGHT WAS A GOOD
EXAMPLE...AND UNDER THE DEVELOPING COLD ADVECTION REGIME...WITHOUT
THE UPPER SUPPORT PASSES BY...IT WILL BE HARD TO GET MORE THAN A
VERY FEW HUNDREDTHS OF PRECIP. THIS IS ABOVE AND BEYOND THE MODEL
DIFFERENCES. THIS WILL LEAVE CHC TO SLIGHT CHANCE POPS FOR LIGHT
SNOW...GENERALLY HIGHER NORTH...FOR TUESDAY NIGHT AND
WEDNESDAY...WITH A LINGERING SLIGHT CHANCE OF LIGHT RAIN/SNOW IN
THE FAR SOUTHEAST OVER PART OF NORTHWEST IA EARLY TUESDAY EVENING.
THIS IS AHEAD OF AND WITH THE VERY STRONG INFLOW OF VERY COLD
AIR...THE ONE THING WHICH IS IN ZERO DOUBT. TEMPERATURES WILL FALL
AT LEAST INTO MID MORNING WEDNESDAY AND SHOW ONLY A SLIGHT RISE
DURING THE DAY...WITH WIND CHILLS DIVING BELOW ZERO AND STAYING
BELOW ZERO..EXCEPT SLIGHTLY LESS COLD FAR SOUTHEAST.

WILL KEEP FLURRIES WITH SOME LINGERING LOW LEVEL MOISTURE WEDNESDAY
NIGHT...AND KEEP JUST DRY AND COLD THURSDAY THROUGH FRIDAY.
NORTHWEST WINDS WILL HOLD UP ENOUGH AHEAD OF THE ARCTIC HIGH TO
BRING IS VERY CLOSE TO WIND CHILL ADVISORY LEVELS BOTH LATE
WEDNESDAY NIGHT AND THURSDAY MORNING. WE MAY HAVE TO LOOK AT THIS
CLOSER TOT HAT TIME SINCE WE HAVE NOT OF COURSE BEEN THIS COLD SO
FAR IN THE SEASON.

THE WEEKEND SEEMS TO OFFER A LITTLE BETTER CHANCE OF SNOW BY SUNDAY
THAN YESTERDAY...WITH OTHER MODELS JOINING THE EC ON THIS. WILL GO
FOR A MENTION SATURDAY NIGHT AND SUNDAY AS PER EXTENDED GUIDANCE.
TEMPERATURES WILL BE A LITTLE LESS COLD...BUT A TESTIMONY TO THE
COLD AIR SHOT COMING IN IS THAT IT LOOKS LIKE DURING THE
WEEKEND...WE WILL ACTUALLY WARM TO HIGHS IN THE TEENS AND LOWS IN
THE SINGLE DIGITS.

FOR DAY SEVEN...NEXT MONDAY...A DRY FORECAST SEEMS IN ORDER...WITH
NOT MUCH TEMPERATURE CHANGE FROM SUNDAY...THAT IS STILL PRETTY COLD.

WITH QUESTIONABLE SNOW AMOUNTS THE NEXT FEW DAYS...TEMPERATURES ARE
IN A SLIGHT AMOUNT OF DOUBT...WITH EVEN A VERY MODEST SNOW COVER
KEEPING READINGS COLDER THAN THIS CURRENT FORECAST.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1115 PM CST MON DEC 2 2013

SUB-VFR CEILINGS HAVE MOVED INTO THE HIGHWAY 14 CORRIDOR ALONG WITH
AREAS OF LOW VISIBILITY IN FOG. STILL SOME QUESTION WHETHER WE WILL
SEE DRIZZLE/FREEZING DRIZZLE WITH THE LOW STRATUS...BUT OPTED TO
KEEP MENTION IN KHON AS WEAK LIFT MOVES IN AHEAD OF SATURATED MID
LEVEL CLOUD BAND. OTHERWISE EXPECT DOWNTREND IN CEILINGS INTO MAINLY
IFR-LIFR RANGE AS LOW LEVEL MOISTURE WRAPS SOUTHWARD ACROSS THE
AREA. MVFR-IFR VISIBILITY IN -SN ALSO BECOMES MORE LIKELY THROUGH
THE LATTER HALF OF THE PERIOD...ESPECIALLY OVER OUR SD/MN COUNTIES
INCLUDING KHON/KFSD.

&&

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

$$

SHORT TERM...SALLY
LONG TERM...
AVIATION...