Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 171751
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1151 AM CST WED DEC 17 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 313 AM CST WED DEC 17 2014

WITH THE RIDGE OF HIGH PRESSURE SHIFTING TO THE EAST TODAY...DON`T
EXPECT MUCH IN THE WAY OF MIXING WITH THE WEAK FLOW.  AND WITH THE
FRESH SNOW COVER...I DECIDED TO GO FEW DEGREES COOLER THAN GUIDANCE.
DID GO A LITTLE WARMER IN AREAS WHERE THE SNOWCOVER IS LACKING. AS
PREVIOUS SHIFTS MENTIONED...QUESTIONS EXIST CONCERNING THE AMOUNT
OF CLOUD COVER THROUGHOUT THE DAY. AT THIS TIME... I FEEL MID
LEVEL WINDS SHOULD KEEP CLOUDS AT BAY DURING THE DAYLIGHT HOURS SO
EXPECT CLOUD DESK TO BETWEEN THE MISSOURI AND JAMES RIVERS.

EXPECT CLOUD COVER TO OVERSPREAD CWA DURING THE EVENING AND INTO THE
POST MIDNIGHT HOURS.  AND HALF TEMPTED TO WARM TEMPERATURES DURING
THE PREDAWN HOURS DUE TO THAT CLOUD COVER.  BUT DECIDED TO SLOW THE
FALL MORE AT THIS TIME AND LET THE LATER SHIFTS TAKE A CLOSER LOOK.
CONTINUED WITH THE WEAK 20 POPS ACROSS THE SOUTH TONIGHT...BUT NOT
TOO CONFIDENT THAT MUCH WILL DEVELOP.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 313 AM CST WED DEC 17 2014

RAPID FIRE SYSTEMS IN ZONAL FLOW ARE LATITUDINALLY DISJOINTED THROUGH
THE MEDIUM RANGE...MAKING PROSPECT FOR LOCATING ANY MEAGER PRECIP
THREAT QUITE SKETCHY. AT THIS POINT IN TIME...PERIOD FROM LATER
THURSDAY THROUGH THE WEEKEND WOULD FAR MORE LIKELY TO REMAIN DRY
THAN ANYTHING ELSE...BUT CERTAINLY IS A NON ZERO THREAT FOR SOME
LIGHT PRECIPITATION.  FIRST SYSTEM ON THURSDAY MAINLY A WEAK FOCUS
OF LOWER TO MID LEVEL ISENTROPIC LIFT...AND FAIRLY WEAK AT THAT.
TEMPS REMAIN COOL ENOUGH TO INVOLVE SOME ICE PROCESSES IN CLOUDS...
WITH DEEPER MOISTURE BRUSHING THROUGH THE SOUTHERN CWA DURING THE
MORNING AND VERY EARLY AFTERNOON. COULD SEE A FEW FLURRIES FARTHER
NORTHWARD...BUT WITH MOISTURE DEPTH STARTING TO LOSE ICE GENERATION
TEMPS DURING THE MIDDAY...EFFICIENCY FOR FLURRIES SEEMS LESS THAN
MENTIONABLE.  BEST DYNAMICS IN THE SHORTER TERM APPEAR TO BE PRESENT
AROUND WAVE WHICH MOVES IN LATE FRIDAY AND FRIDAY NIGHT...WITH
DISTINCT PV FEATURE DIGGING PAST. HOWEVER...AT THIS TIME THERE IS
ALMOST NO THERMAL STRUCTURE AROUND TO FOCUS ANY LIFT...AND CERTAINLY
WARM ENOUGH WITH LAYER OF DRYING OFF SURFACE TO SUGGEST LACK OF
MEASURABLE THREAT.

DESPITE QUITE A BIT OF LOW LEVEL MOISTURE WHICH HANGS AROUND INTO
THE WEEKEND...WILL EBB AND FLOW IN BOTH DEPTH AND LOCATION AS FLOW
ALOFT IS INDUCED INTO A MORE WESTERLY COMPONENT AT TIMES. THIS TIME
AROUND...INVERSION NOT QUITE AS FORMIDABLE...AND SHOULD BE A BIT
EASIER FOR SOME MORE SIGNIFICANT EAST/WEST SWINGS IN CLOUD LOCATION
AS WAVES MOVE PAST. MOST FLOW CHANGE IMPACT LOOKS TO OCCUR ALOFT...
WITH A PRETTY STEADY SOUTHWEST TO SOUTHEAST NEAR SURFACE WIND
PERSISTING INTO THE WEEKEND. OVERALL...THE SHALLOW MOIST LAYER AND
LACK OF ANY SIGNIFICANT LIFT FORCING FOR THIS LAYER WOULD SUGGEST
PRECIPITATION DEVELOPMENT MUCH MORE LIKELY TO NOT OCCUR...THAN TO
OCCUR. ONE THING TO KEEP IN MIND IS THAT TYPE WOULD LIKELY BE A
FREEZING DRIZZLE/DRIZZLE WITH ANY SHALLOW PRECIPITATION THAT WOULD
DEVELOP. FRIDAY NIGHT INTO EARLY SATURDAY WOULD BE ONE PERIOD TO
WATCH.

TEMPERATURES OVER THE PERIOD WILL GRADUALLY START TO SHOW LESS
DIURNAL VARIABILITY OVERALL...AS CLOUDS...MILDER AIRMASS AND
PERSISTENT SOUTHERLY FLOW TAKES HOLD THROUGH SUNDAY. DEEPER SNOW
COVER TO THE WEST ALONG WITH PROSPECT FOR BRIEF CLEARING PERIODS
WOULD SUGGEST SLIGHTLY LARGER RANGES IN THE WEST. HIGHS STARTING
BELOW NORMAL IN THE 20S TO AROUND 30 ON THURSDAY WILL MODERATE
TOWARD WIDESPREAD 30S ON SATURDAY AND SUNDAY...WITH LOWS TEENS
WESTERN SNOWCOVERED AREAS TO MAINLY 20S EAST...BUT VERY EASILY BY
SATURDAY NIGHT COULD BE SOMEWHAT MILDER THAN CURRENTLY EXPECT IN THE
EAST.

FOR THE END OF THE EXTENDED PERIOD...SUNDAY NIGHT THROUGH TUESDAY...
GIVEN THE LONGWAVE PATTERN...WOULD TEND TO PLACE A BIT MORE
CONFIDENCE IN A SOLUTION WHICH HAS WAVE DIGGING AND AMPLIFYING
ACROSS THE NORTHERN PLAINS ON SUNDAY NIGHT THROUGH MONDAY...SUCH AS
THE ECMWF...ALTHOUGH THE GFS GETS THERE AS WELL...JUST 12-18 HOURS
LATER.  TEMPS ALOFT ARE WARM ENOUGH TO SUGGEST MOSTLY A LIQUID
THREAT SUNDAY NIGHT WITH ANY PRECIPITATION...WHICH WOULD FORM IN
WARM AIR ADVECTION WING OF DIGGING SYSTEM...MAINLY BRIEFLY IMPACTING
THE EASTERN CWA...IF AT ALL. TEMPS AT SURFACE SUCH THAT MAY BE A BIT
OF A LIGHT FREEZING RAIN CONCERN...BUT PATTERN ALSO SUGGESTS THAT
MAY BE A BIT COOL ON TEMPS DURING THIS TIME.  CLOSING OFF SYSTEM IN
THE NORTHERN PLAINS ON MONDAY WILL BRING ALONG WITH IT POTENTIAL FOR
SOME BULK COOLING AND MORE PRECIP TYPE ISSUES. AT THIS POINT...WILL
STICK GENERALLY WITH A RAIN/SNOW MIX THREAT TO ACCOUNT FOR
UNCERTAINTY...BUT EXIT OF SYSTEM SHOULD END WITH PRIMARILY A SNOW
CHANCE FROM LATER MONDAY NIGHT THROUGH TUESDAY...ALONG WITH QUITE A
BIT OF WIND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1142 AM CST WED DEC 17 2014

CURRENTLY VFR CONDITIONS ACROSS MOST OF THE AREA...WITH IFR AND
MVFR CIGS LINGERING IN CENTRAL SOUTH DAKOTA. CLOUDS WILL INCREASE
TONIGHT INTO TOMORROW...BUT CURRENTLY THINKING MOST LOCATIONS STAY
VFR. WILL HAVE TO WATCH THE STRATUS DECK OUT WEST...AS IT COULD
TRY TO PUSH BACK NORTH AND POTENTIALLY EXPAND LATER TONIGHT. THUS
DECIDED TO MOVE MVFR CIGS BACK INTO KHON TONIGHT. BUT AGAIN
MODELS ARE INCONSISTENT AND NOT OF MUCH USE WITH THIS LOWER
STRATUS. SO WILL MAINLY BE A WATCH AND SEE WITH REGARD TO FLIGHT
CONDITIONS TONIGHT INTO TOMORROW...BUT AT THIS TIME LEANING
TOWARDS MAINLY VFR EAST OF THE JAMES RIVER.

&&

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

$$

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



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