Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 260916
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
416 AM CDT SUN OCT 26 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 415 AM CDT SUN OCT 26 2014

ONE MORE DAY OF WELL ABOVE NORMAL TEMPERATURES EXPECTED ACROSS THE
REGION. GRADIENT INCREASES SO IT WILL BE A BREEZY DAY THOUGH...WITH
SOUTHEASTERLY WINDS GUSTING TO AROUND 30 MPH. THIS WIND COMBINED
WITH LOW HUMIDITY...WILL RESULT IN VERY HIGH FIRE DANGER ACROSS
PORTIONS OF SOUTHWEST MINNESOTA AND ADJACENT NORTHWEST IOWA. FEEL
LIKE RELATIVE HUMIDITY WILL GENERALLY STAY HIGH ENOUGH TO PREVENT
ANY RED FLAG CRITERIA.

STILL UNCERTAINTY ON STRATUS DEVELOPMENT THIS MORNING. LOW LEVELS
REMAIN QUITE DRY...HOWEVER MODELS SHOW A NARROW CORRIDOR OF
MOISTENING AROUND 850 MB. NAM AND GFS SATURATE THIS
LEVEL...RESULTING IN A CORRIDOR OF STRATUS MOVING NORTHEAST ACROSS
THE CWA. RAP AND HRRR STAY SHORT OF SATURATING THEY LAYER...AND THUS
KEEP IT SUNNY. AT THIS TIME NO REAL WAY TO TELL WHICH IS
CORRECT...SO WILL GO WITH A COMPROMISE AND MONITOR TRENDS OVER THE
COMING HOURS. GIVEN THE LOWER SURFACE DEWPOINTS THAN ORIGINALLY
FORECAST...CONFIDENCE IS HOWEVER GROWING THAT DIURNALLY DRIVEN
STRATOCU GENERATION IS UNLIKELY. THUS THINKING ANY STRATUS THAT DOES
FORM WILL QUICKLY SHIFT NORTHEAST THROUGH THE MORNING AND EARLY
AFTERNOON...WITH MOSTLY SUNNY SKIES RETURNING IN ITS WAKE. SO
OVERALL...EXPECTING MORE SUN THAN CLOUDS TODAY OVER THE CWA. GIVEN
THIS...AND WARMING TEMPERATURES ALOFT...WILL CONTINUE ON THE WARMER
SIDE OF GUIDANCE...UPPER 60S SOUTHWEST MINNESOTA TO MID AND UPPER
70S ALONG THE MISSOURI RIVER AND WEST OF THE JAMES.

COLD FRONT WILL WORK ITS WAY ACROSS THE AREA TONIGHT WITH WINDS
TURNING NORTHERLY BEHIND IT. ANOTHER SURGE OF LOW LEVEL MOISTURE
EXPECTED AHEAD OF THE FRONT...AND WORRIED WE COULD SEE STRATUS
DEVELOPMENT AFTER SUNSET EAST OF INTERSTATE 29. ALSO STARTING TO
THINK WE MAY SEE FOG FORMATION ON THE EDGE OF THIS STRATUS...WHERE
THE SURFACE TROUGH AXIS WILL RESULT IN LIGHT SURFACE WINDS...AND
MOSTLY CLEAR SKIES SHOULD ALLOW FOR TEMPERATURES TO DROP TOWARDS THE
RELATIVELY HIGH DEWPOINT VALUES WE WILL HAVE. THUS ADDED SOME FOG
INTO THE GRIDS FOR NORTHWEST IOWA AND ADJACENT SOUTHWEST MINNESOTA.
COULD POTENTIALLY BE A BIT FURTHER WEST TO...SO SOMETHING TO WATCH.

FORCING INCREASES TONIGHT AS A WAVE APPROACHES FROM THE WEST. THINK
WE COULD BEGIN TO SEE SHOWERS DEVELOP ALONG THE ELEVATED FRONT BY
12Z ACROSS OUR SOUTH CENTRAL SOUTH DAKOTA ZONES...SO WENT AHEAD AND
ADDED SOME POPS INTO THAT REGION. SHOULD GENERALLY BE A MILD NIGHT
WITH LOWS IN THE MID 40S TO LOW 50S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 415 AM CDT SUN OCT 26 2014

COULD VERY WELL BE SOME LINGERING FOG IN NORTHWEST IA THROUGH
MID MORNING MONDAY...BEHIND WHAT MAY BE DEPARTING STRATUS PLACING
THAT AREA IN A FAVORABLE ZONE FOR FOG DEVELOPMENT. OTHERWISE MONDAY
IS HIGHLIGHTED BY OUR WELL ADVERTISED MID AND UPPER WAVE PASSING
ACROSS THIS AREA. THE WAVE IS OPEN AND NOT REAL ORGANIZED...AT LEAST
WITH THE JET DYNAMICS AND UPPER QG FORCING. THE NAM IS MOST BULLISH
WITH THE MOISTURE DEPTH FROM 850-500MB THROUGH MUCH OF THE AREA. THE
GFS AND ECMWF ARE A LITTLE LESS SO...AND ALSO QUICKER WITH THE WAVE
PASSAGE WHICH LOOKS PREFERABLE TO THE SLOWER NAM. WITH THE WAVE OPEN
NOT SURE WHAT WOULD HANG IT UP AS PER THE NAM SOLUTION. BUT ONE
THING THE MODELS ARE IN GOOD AGREEMENT ON IS SHOWING THE PLACEMENT
OF THE LOW AND MID LEVEL FRONTOGENESIS. THE FRONTAL BOUNDARY IS
SLOPED QUITE STRONGLY...WITH THE 850MB FRONTOGENESIS FAVORING
NORTHWEST IA WHERE LIMITED MOISTURE EXISTS AT THAT LEVEL. BUT
FURTHER NORTH...THE 700-600MB FRONTOGENESIS TAKES OVER AND THIS IS
WHERE THE HIGHEST POPS ARE PLACED. STILL...WITH THE SKITTISHNESS OF
THE OVERALL DYNAMICS AND MOISTURE PROFILE...KEPT POPS MAINLY ONLY IN
THE CHANCE CATEGORY FOR LIGHT RAINFALL. SURFACE WINDS WILL BECOME
NORTHWESTERLY AND WILL BECOME QUITE BREEZY BY AFTERNOON. IN OUR FAR
WESTERN ZONES...THE GRASSLAND FIRE DANGER INDEX STAYS JUST INSIDE
THE HIGH CATEGORY...AS MINIMUM HUMIDITY VALUES LOOK A BIT TOO
HIGH...AND WIND SPEEDS A LITTLE TOO LOW TO WARRANT A VERY HIGH INDEX
AT THIS TIME. CONCERNING TEMPERATURES...COMPARED TO WHAT WE HAVE
BEEN HAVING LATELY...COOLER AIR WILL BE ADVECTING IN GIVING HIGHS IN
THE UPPER 50S TO MID 60S...WHICH IS STILL A LITTLE ABOVE NORMAL.

BUT THIS WILL CHANGE ON TUESDAY...AS COLD AIR ADVECTION CONTINUES TO
POUR IN THROUGH MONDAY NIGHT ALONG A SECOND WAVE ON THE BACKSIDE OF
THE PARENT UPPER TROUGH. HIGHS ON TUESDAY ONLY LOOK TO BE GENERALLY
IN THE RANGE OF 50 TO 55 DEGREES. AND WITH STOUT NORTHWEST WINDS OF
20 TO 30 MPH...WITH POTENTIALLY HIGHER GUSTS...THAT WILL ADD AN
EXTRA CHILL TO THE AIR. IN ADDITION...ALL OF THE VARIOUS
DETERMINISTIC MODELS ARE SHOWING A LOT OF MOISTURE IN THE 850-800MB
LAYER...GENERALLY BISECTING THE FORECAST AREA FROM NEAR HURON...TO
SIOUX FALLS AND STORM LAKE IOWA. ANYTHING ALONG AND NORTHEAST OF
THAT LINE WILL LIKELY BE CONSIDERABLY CLOUDY THROUGH THE DAY...WITH
INCREASINGLY SUNNY CONDITIONS HEADING TOWARD OUR SOUTHWEST ZONES.
THE FIRE DANGER ONCE AGAIN WILL BE ELEVATED IN THE HIGH CATEGORY...
BUT RIGHT NOW HUMIDITY VALUES LOOK TOO HIGH TO PLACE THE INDEX IN
THE VERY HIGH CATEGORY. FOR TUESDAY NIGHT...WITH WINDS DECREASING
DRAMATICALLY AND CLEARING SKIES...LOWS WILL LIKELY BE ON THE COOL
SIDE OF MANY OF THE GUIDANCE VALUES. BECAUSE OF THIS...CHOSE TO GO
WITH THE BIAS CORRECTED RAW VALUES WHICH GAVE THE COOLEST LOW
TEMPERATURES OF AT OR JUST BELOW FREEZING.

FROM WEDNESDAY THROUGH SATURDAY...THE FORECAST STILL LOOKS DRY AND
COOL. THE DETERMINISTIC GFS AND ECMWF FOR THE MOST PART ARE IN GOOD
AGREEMENT THROUGH SATURDAY WHICH MAKES THE FORECAST EASIER. THERE IS
ONE WEAK WAVE WHICH MOVES THROUGH WEDNESDAY AFTERNOON AND EVENING.
ANOTHER STRONGER AND COLD SHORT WAVE DIVES DOWN THE FLOW THURSDAY
NIGHT. THE ECMWF IS STRONGER WITH THIS SECOND FEATURE AND LIKELY
BETTER AS THE GFS LOOKS TOO WASHED OUT WITH THE WAVE. THEREFORE
CONTINUED TO BLEND SOME OF THE COOLER ECMWF VALUES INTO THE
CONSENSUS TEMPERATURES FOR LATE THIS WEEK.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1041 PM CDT SAT OCT 25 2014
VFR CONDITIONS EXPECTED THROUGH 12Z/26. SOUTHERLY FLOW INCREASING
ACROSS THE AREA WITH MARGINAL LOW LEVEL JET AT KHON. FURTHER EAST
THE LOW LEVEL JET IS EXPECTED TO BE SLIGHTLY WEAKER....SO DID NOT
INCLUDE IN THE FORECAST. MVFR STRATUS IS EXPECTED TO DEVELOP
ACROSS NEBRASKA AND LIFT NORTHEAST ACROSS SOUTHEAST SOUTH DAKOTA
INTO MINNESOTA AND IOWA. HAVE INCLUDED SOME LOWER CEILINGS AT BOTH
KFSD AND KSUX. QUESTIONS REMAINS AS TO WHETHER THE CEILING WILL
MIX OUT...OR WILL HANG TOUGH THROUGHOUT THE AFTERNOON AND EVENING
HOURS SUNDAY NIGHT.


&&

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

$$

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



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