Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 281128
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
628 AM CDT TUE OCT 28 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 337 AM CDT TUE OCT 28 2014

NEXT SURGE OF COOL AIR IS COMING DOWN AT THIS TIME...WITH PLENTY OF
COLD AIR ADVECTION CLOUDS HEADING SOUTHEASTWARD WITH THE CHILLY AIR.
THE CLOUD COVER MAY HAVE TROUBLE MAKING IT DOWN TO THE SOUTHERN
REACHES OF THE FORECAST AREA FROM GREGORY COUNTY TO SIOUX CITY. BUT
OTHERWISE THE RAP13 AND NAM12 MODELS SHOW AMPLE MOISTURE
EVERYWHERE ELSE THROUGH MIDDAY IN THE 850-800MB LAYER...SLOWLY
ERODING FROM SOUTHWEST TO NORTHEAST THROUGH THE AFTERNOON. COULD BE
A SPRINKLE OR VERY LIGHT SHOWER IN OUR FAR NORTHEAST ZONES THROUGH
MIDDAY...BUT ANY RAINFALL WILL HAVE A LOT OF TROUBLE MEASURING.
HIGH TEMPERATURES FOR TODAY DID NOT NEED TO BE CHANGED MUCH...AND
OVERALL NOT MOVING A WHOLE LOT FROM CURRENT READINGS. GENERALLY
LOOKING AT 50 TO 55 DEGREES WHERE SOME AFTERNOON PARTIAL SUNSHINE
COULD OCCUR...GENERALLY ALONG THE MO RIVER VALLEY. BUT MANY
OTHER AREAS WILL LIKELY STAY IN THE 40S. WINDS WILL BE BRISK TODAY
BUT WINDS IN THE MIXED LAYER SUGGEST A WIND ADVISORY IS NOT NEEDED.
HUMIDITY VALUES SHOULD BE WELL HIGH ENOUGH TO PRECLUDE ANY THOUGHT
FOR A RED FLAG WARNING.

TONIGHT...THE LAST REMNANTS OF THE STRATOCUMULUS CLOUDS WILL EXIT
SOUTHWEST MN DURING THE EVENING. THEREFORE EXPECTING CLEAR SKIES
THROUGHOUT THE ENTIRE AREA AFTER EVENING. WITH WINDS DECREASING
RAPIDLY...LOOKS LIKE A GOOD NIGHT TO GO WITH THE COLDEST GUIDANCE
READINGS SUCH AS THE WEIGHTED MODEL...BIAS CORRECTED RAW VALUES AND
SOME GEMBC/ECMWFBC. THE LOCATIONS WHICH COULD GET DOWN INTO THE 20
TO 25 DEGREES ARE IN OUR WESTERN ZONES RIGHT ALONG THE SURFACE RIDGE
AXIS. THEREFORE PLACES LIKE HURON AND CHAMBERLAIN COULD SNEAK DOWN
EVEN A BIT COOLER THAN THE 24 DEGREES WHICH IS FORECAST. CONVERSELY
OUR FAR EASTERN ZONES SHOULD STAY IN THE LOWER 30S WHERE SOME
NORTHWEST WIND WILL REMAIN THROUGH THE NIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 337 AM CDT TUE OCT 28 2014

HIGH PRESSURE MOVES OFF TO THE EAST ON WEDNESDAY...WITH LIGHT
SOUTHERLY RETURN FLOW DEVELOPING. WILL SEE SLOW WARMING ALOFT AS
SHORTWAVE RIDGING BUILDS IN...BUT WITH RELATIVELY POOR MIXING AND
WARMER AIR SLOWER ON RECENT MODEL RUNS...DIS BUMP HIGHS DOWN A
BIT...WITH MOST LOCATIONS IN THE 50S. A WAVE WILL PUSH ACROSS THE
AREA WEDNESDAY NIGHT IN THE QUICK NORTHWEST FLOW ALOFT. QUITE A BIT
OF DRY AIR...SO MAINLY JUST THINKING WE SEE INCREASING CLOUDS LATER
WEDNESDAY INTO WEDNESDAY NIGHT...BUT CAN NOT RULE OUT A FEW LIGHT
RAIN SHOWERS WEDNESDAY NIGHT ACROSS THE NORTHEAST HALF OF THE AREA
WHERE SLIGHTLY BETTER MOISTURE IS LOCATED.

WINDS TURN NORTHWESTERLY BEHIND THE WAVE FOR THURSDAY...AND SHOULD
THUS SEE BETTER MIXING IN THE COLD AIR ADVECTION REGIME. SO DESPITE
THESE COLDER TEMPERATURES MOVING IN ALOFT WE SHOULD END UP WARMER
THAN WEDNESDAY...WITH HIGHS IN THE MID 50S TO LOW 60S. THE COLDER
AIR CONTINUES TO FILTER INTO THE REGION THURSDAY NIGHT. WILL LIKELY
BE A COLD ONE ACROSS THE REGION...ALTHOUGH A BIT UNCERTAIN HOW COLD.
DESPITE THE SURFACE RIDGE NEARBY...DECENT FLOW ALOFT MAY KEEP US
SLIGHTLY MIXED THROUGH THE NIGHT. THUS FOR NOW DID NOT WANT TO GO
QUITE AS COLD AS SOME OF THE MOS...AND WILL KEEP THINGS IN THE MID
20S TO AROUND 30. WITH THE HIGH MOVING EAST...FRIDAY SHOULD BE
ANOTHER DAY THAT DESPITE WARMING ALOFT...WE END UP COLDER AT THE
SURFACE WITH WEAK MIXING IN THE EASTERLY FLOW. HIGHS WILL PROBABLY BE
STUCK IN THE 40S...POSSIBLY MAKING IT THE COLDEST DAY WE HAVE SEEN
IN A WHILE.

THE WEEKEND WILL START WITH A LARGE UPPER RIDGE OVER THE CENTRAL
US...WITH TROUGHS ON BOTH COASTS. PROBABLY WILL NOT REALIZE MUCH OF
THE WARMING ALOFT ON SATURDAY...AND TRENDED HIGHS DOWN SOME...GIVING
ANOTHER DAY IN THE 40S AND 50S. WITH THE SURFACE GRADIENT INCREASING
WILL ALSO BE QUITE WINDY. AT THIS TIME LOOKS LIKE WE SHOULD STAY
BELOW ADVISORY LEVELS...BUT SOUTHERLY WINDS GUSTING TO 35 MPH SEEM
PROBABLE. BY SUNDAY THE WEST COAST TROUGH BEGINS TO MOVE INTO THE
PLAINS...TURNING THE FLOW SOUTHWESTERLY...RESULTING IN BETTER MIXING
INTO THE WARMER TEMPERATURES ALOFT. THUS SUNDAY COULD BE PRETTY
NICE...RETURNING INTO THE 60S FOR SOME OR MOST OF THE CWA.

PRECIPITATION CHANCES DO NOT LOOK THAT GREAT WITH THIS TROUGH...WITH
THE BETTER FORCING SPLITTING OUR AREA TO THE NORTH AND SOUTH. AT
THIS TIME SEEMS LIKE THE BEST CHANCE FOR SOME SHOWERS COULD END UP
BEING SUNDAY NIGHT...WHEN GUIDANCE SUGGESTS OUR AREA MAY BRIEFLY GET
INTO SOME BETTER QG FORCING IN BETWEEN THE TWO MAIN WAVES. OF COURSE
THIS IS STILL A WAYS OUT AND THUS CONFIDENCE ON EXACT EVOLUTION
REMAINS LOW. BY MONDAY WE SHOULD BE ON THE COOLER SIDE OF THE
FRONT...BUT NOT MUCH COLD AIR BEHIND THIS WAVE...AND THUS SHOULD
STILL BE IN THE 50S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 622 AM CDT TUE OCT 28 2014

AS STRATOCUMULUS CLOUDS CONTINUE TO MOVE SOUTHEASTWARD DUE TO COLD
AIR ADVECTION...THE MORNING HOURS WILL CERTAINLY SEE MVFR TO LOWER
END VFR CEILINGS FOR MOST AREAS IN THE FORECAST AREA. KHON AND
KFSD ARE A TOUGH CALL...WHETHER TO LEAVE THEM AT UPPER END MVFR OR
LOWER END VFR. PLENTY OF MVFR CEILINGS EXIST TO THE NORTH OF THE
FORECAST AREA...BUT THERE IS A QUESTION OF HOW MUCH OF THAT WILL
MAKE IT SOUTHWARD WITH A DEEPER MIXED LAYER IN THIS FORECAST AREA.
BUT IT APPEARS FROM THE VIS FOG IR SATELLITE CURVE THAT THERE IS A
SLIGHT DISCOLORATION MARKING THE DIFFERENCE BETWEEN MVFR AND
VFR...EDGING SOUTHWARD RAPIDLY TOWARD KHON AND PROBABLY WITHIN AN
HOUR OR SO AT KFSD. SO WENT AHEAD AND PREDOMINANTLY WENT MVFR AT
KHON THIS MORNING...WITH A TEMPO GROUP FOR MVFR AT KFSD. THE SITES
SHOULD MIX TO VFR THIS AFTERNOON...WITH A BRISK NORTHWEST WIND
CONTINUING OF GUSTS AROUND 25 TO 28 KNOTS. AT THIS TIME...IT
APPEARS THE STRATOCUMULUS MAY HAVE A MORE DIFFICULT TIME MAKING IT
TO KSUX...SO FOR NOW JUST KEPT IT SCATTERED AT THAT LOCATION.
TONIGHT...WINDS AND CLOUDS WILL RAPIDLY DECREASE THIS EVENING
LEAVING VFR.

&&

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

$$

SHORT TERM...MJ
LONG TERM...CHENARD
AVIATION...MJ



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