Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 282054
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
254 PM CST FRI NOV 28 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 231 PM CST FRI NOV 28 2014

MAIN QUESTION TONIGHT IS FOG POTENTIAL OR NOT. THE NAM AND RAP
CONTINUE TO SHOW A LOT OF FOG DEVELOPMENT THROUGHOUT MUCH OF
NORTHWEST IA...SOUTHWEST MN...PARTS OF SOUTHEAST SD AND EAST CENTRAL
SD. THEY BEGIN THE FOG DEVELOPMENT THIS EVENING ACROSS FAR NORTHWEST
IA...THEN EXPAND IT WEST AND NORTHWARD. THE NAM AND RAP ARE VERY
MOIST WITH THEIR RESPECTIVE SURFACE DEW POINT DEPRESSIONS...IN FACT
SHOWING A LOT OF 1 TO 2 DEGREE DEW POINT DEPRESSION SPREADS EVEN AT
THIS TIME WHICH IS NOT VERIFYING. THE GFS...ECMWF AND ARW ARE MUCH
MORE SUBDUED...SHOWING WIDER DEW POINT DEPRESSIONS AND THUS LESS
FOG. FOR NOW...KEPT AREAS OF FOG GOING FROM THE BROOKINGS AREA
SOUTHEASTWARD THROUGH OUR EASTERN ZONES. THIS MATCHES UP WITH THE
SMALL DEW POINT DEPRESSIONS ADVERTISED BY THE ECMWF IN THOSE
AREAS...WITH PATCHY FOG FOR ADJACENT AREAS TO THE WEST...NOT BUYING
THE NAM OR RAP OUTPUT. LATE TONIGHT A WELL DEFINED WARM FRONT BEGINS
TO NUDGE EASTWARD HELPING TO ACTUALLY WARM TEMPERATURES ACROSS THIS
AREA. THIS MAY ALSO HELP IN REDUCING FOG POTENTIAL...AT LEAST WEST
OF I 29. FOR TEMPERATURES...LOADED UP THE CHILLY GEM BIAS CORRECTED
VALUES FROM SOUTHWEST MN THROUGH THE IA GREAT LAKES REGION...WITH A
LOT OF ECMWF ELSEWHERE.

SATURDAY SHOULD BE A WARM DAY AHEAD OF THE NEXT CANADIAN FRONT...
WHICH WILL MAKE ITS PRESENCE FELT IN OUR NORTHERN ZONES BY
AFTERNOON. THEREFORE LOOKING AT SLOWLY FALLING TEMPERATURES NORTH OF
I 90 DURING THE AFTERNOON...BUT WITH READINGS STILL FAIRLY MILD.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 231 PM CST FRI NOV 28 2014

IN THE MEDIUM TO LONG RANGE...PATTERN BEGINS TO SHIFT EARLY IN THE
WORK WEEK AS WE TRANSITION TO A MOSTLY WESTERLY ZONAL FLOW WHICH
WILL EVENTUALLY MODERATE TEMPERATURES TO NEAR NORMAL READINGS.

ON SATURDAY NIGHT ANOTHER SHOT OF COLD AIR WILL MOVE INTO THE AREA
BEHIND A COLD FRONT WITH LOWS FROM THE SINGLE DIGITS NORTH OF I-90
TO THE TEENS ELSEWHERE. THERE IS THE POTENTIAL FOR FLURRIES ALONG
AND JUST BEHIND THE FRONT SO HAVE KEPT IN CHANCE FOR THAT TIME.

SURFACE HIGH PRESSURE BUILDS IN AND WILL CONTINUE TO DRAG COLD AIR
IN WITH THE COLDEST AIR OVER US ON SUNDAY NIGHT.  EXPECT LOWS ON SUN
NIGHT TO BE IN THE SINGLE DIGITS WITH SOME AREAS...ESPECIALLY
NORTH...SEEING TEMPS AROUND -3 TO -4.  VERY COLD TEMPS COMBINED WITH
5-10 MPH WIND WILL RESULT IN WIND CHILL VALUES OF -10 TO -20 RIGHT
AROUND THE MORNING COMMUTE. NOT MUCH OF A REBOUND IN TEMPS EXPECED
ON MONDAY WITH HIGHS IN THE TEENS TO LOW 20S.

FOR TUESDAY TO FRIDAY...NO SENSIBLE WEATHER TO SPEAK OF AS ZONAL
FLOW DOMINATES.  TEMPS WILL CONTINUE TO INCH TOWARD MORE SEASONABLE
READINGS BY THURS/FRI.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1137 AM CST FRI NOV 28 2014

VFR WILL CERTAINLY PREVAIL TODAY. THERE IS MORE OF A QUESTION MARK
TONIGHT. THERE ARE STILL SOME INDICATIONS LOOKING AT THE VARIOUS
SHORT RANGE ENSEMBLES THAT LOW CEILINGS AND VISIBILITIES WILL
FIRST SETUP OVER EXTREME NORTHWEST IA AFTER SUNSET...THEN WORK
NORTH AND NORTHWEST POTENTIALLY AFFECTING THE KFSD TAF SITE.
CURRENTLY EXTREME NORTHWEST IA AND SOUTHWEST MN DO EXHIBIT SMALL
SURFACE DEW POINT DEPRESSIONS...SO THIS SCENARIO IS PLAUSIBLE.
THERE IS A QUESTION HOWEVER...BECAUSE IT IS PRIMARILY THE NAM AND
RAP WHICH ARE SHOWING THIS...WHILE MANY OF THE OTHER MODELS ARE
NOT. SO ENOUGH UNCERTAINTY EXISTS THAT WE STILL DO NOT WANT TO GO
ALL IN FOR FOG AND LOW CEILINGS FOR KFSD. IT APPEARS THAT KSUX
WILL BE TOO FAR WEST IF THIS SCENARIO WERE TO PAN OUT...AND THAT
KHON MAY BE MORE IMPACTED BY JUST THE USUAL MVFR LATE NIGHT LIGHT
FOG WITH A SOUTHERLY FLOW. KEPT KSUX VFR...AND KFSD MVFR FOR NOW
FOR TONIGHT.


&&

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

$$

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


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