Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 011735
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1235 PM CDT MON SEP 1 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 428 AM CDT MON SEP 1 2014

UPPER LOW OVER THE CWA EARLY THIS MORNING GENERATING ISOLATED TO
SCATTERED SHOWERS. THESE ARE IN A WEAKENING STATE...AND THINKING
SHOULD GENERALLY BE DRY BY 12Z. WILL LIKELY SEE SOME CU AND
EVENTUALLY SOME CIRRUS MOVING IN FROM THE WEST TODAY...BUT SHOULD
GENERALLY BE A PARTLY TO MOSTLY SUNNY DAY. BASED ON THERMAL FIELDS
AND EXPECTED SUNSHINE...DID BUMP UP HIGHS A BIT...LOOKING FOR MID TO
UPPER 70S OVER THE AREA. A WAVE CURRENTLY ENTERING WYOMING WILL
QUICKLY PUSH EAST TODAY...MOVING OVER OUR AREA LATER THIS AFTERNOON
AND EVENING. PRETTY GOOD UPPER LEVEL FORCING WITH THIS WAVE...BUT WE
LACK A LOW LEVEL FORCING MECHANISM. CAP IS RELATIVELY SMALL...BUT
WITHOUT THIS FORCING MECHANISM...THINK IT WILL PROBABLY HOLD OVER
MOST OF THE AREA THIS AFTERNOON...KEEPING IT MAINLY DRY.

THERE DOES APPEAR TO BE AN AREA OF LOCALLY ENHANCED CONVERGENCE
ACROSS WESTERN MINNESOTA...AND HI RES MODELS ARE ALL SHOWING
DEVELOPMENT IN THIS AREA. THINK MOST OF THE SHOWERS AND STORMS IN
THIS AREA WILL PROBABLY STAY NORTHEAST OF OUR CWA...BUT INCLUDED
SOME LOW POPS NEAR MARSHALL. OTHER AREA WHERE STORMS MAY DEVELOP
THIS AFTERNOON IS ACROSS THE WESTERN PLAINS. THESE WILL TRACK
EAST...POSSIBLY APPROACHING CHAMBERLAIN AND GREGORY BY AROUND 0Z.
THUS ALSO WILL CARRY SOME POPS IN THIS AREA. GIVEN MINIMAL
CAPE...NOT MUCH OF A SEVERE THREAT...ALTHOUGH COULD BE SOME STRONG
WINDS WITH THE ACTIVITY ACROSS THE WESTERN PLAINS...POSSIBLY GETTING
INTO OUR SOUTH CENTRAL SOUTH DAKOTA COUNTIES. THINK MOST OF THE
ACTIVITY WILL DISSIPATE AFTER SUNSET...AND THUS WILL KEEP THE
FORECAST DRY IN BETWEEN THE TWO AREAS MENTIONED ABOVE. ALTHOUGH IF
WE HEAT ENOUGH...NOT OUT OF THE QUESTION WE COULD SEE AN ISOLATED
THUNDERSTORM JUST ABOUT ANYWHERE. SKIES CLEAR TONIGHT...BUT WE MAY
HOLD ON TO JUST ENOUGH OF A BREEZE TO PREVENT TEMPS FROM FALLING TOO
LOW...THOUGH STILL EXPECTING MID 50S.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 428 AM CDT MON SEP 1 2014

TUESDAY WILL OVERALL BE A PLEASANT DAY ACROSS THE AREA...AS
SURFACE RIDGE SLIPS SOUTHEAST...WITH ZONAL FLOW WORKING TOWARD
WEAK RIDGING. POTENTIAL FOR MID LEVEL BOUNDARY TO GET CAUGHT UP
JUST TO THE SOUTH OF THE AREA DURING THE DAY...SO COULD GET A FEW
HARMLESS MID CLOUDS ACROSS THE SOUTH...AND A SPILLOVER OF A FEW
HIGHER CLOUDS INTO THE NORTHERN AREAS. HIGHS WILL BE SEASONABLE IN
THE UPPER 70S AND LOWER 80S.

ON TUESDAY NIGHT...INCREASE IN MID LEVEL WARM AIR ADVECTION AND
PUSH OF THE ELEVATED MIXED LAYER INTO THE SOUTHWESTERN CWA. JUST
ENOUGH CONVERGENCE AND WEAK QG FORCING TO BE CONCERNED TOWARD THE
LATTER HALF OF THE NIGHT...AS BOUNDARY PUSHES SLOWLY NORTHEAST.ADDED
IN AN ISOLATED LEVEL POP FOR ELEVATED SHOWERS NORTH OF A HURON TO
SIOUX FALLS TO SPENCER LINE...BUT LOOKS LIKE ANY THUNDER IN A 50
J/KG MAX CAPE ENVIRONMENT WOULD BE EVEN MORE ROGUE THAN THE SHOWERS.
KEPT A SMALL LINGERING CHANCE DURING THE MORNING ACROSS SOUTHWEST
MINNESOTA AND EAST CENTRAL SD...BUT BOUNDARY SHOULD NOT WAIT
AROUND FOR LONG AS WEAK WAVE MOVES PAST.

WILL LIKELY HAVE SOME STRATUS BUILDING NORTHWARD ON TUESDAY NIGHT
ACROSS NEBRASKA...WITH A LATE NIGHT PULSE IN COVERAGE AS HIGHER
DEWPOINTS SNEAK IN BELOW WARMING TEMPS ALOFT. THIS STRATUS IS
ALMOST UNANIMOUSLY UNDERDONE IN MODEL SOLUTIONS...AND HAVE SOME
CONCERN THAT IT WILL NOT GO AWAY QUITE AS QUIETLY AS NAM/GFS/
CANADIAN/ECMWF SUGGEST. POTENTIAL IS THERE TO MESS UP WHAT WILL
LIKELY BE THE FINAL OF THE WARMER DAYS FOR A WHILE...AT LEAST
ACROSS SW MN AND NW IA...WHILE LOOKS A BIT MORE CERTAIN WITH
VEERING LOW LEVEL FLOW THAT THE WEST WILL BREAK OUT MORE READILY.
FOR NOW...HAVE SOME READINGS APPROACHING 90 IN THE WEST...AND HAVE
LOWER TO MID 80S IN THE EAST. WITH THE WARMER AND MUCH MORE HUMID
AIR MASS...THERMODYNAMICS PROFILES ARE CONCERNING GIVEN THE
3000-3500 J/KG MEAN CAPE BETWEEN OPERATIONAL MODELS...UNTIL
CONSIDERING THAT MID LEVEL BOUNDARY PUSHED NORTHEAST DURING THE
MORNING...AND THERE IS A GOOD SOLID 75-150 J/KG CAP ON THINGS...
ALONG WITH NEXT TO NO LARGER SCALE LIFT FORCING.

IN FACT...SHOULD BE CAPPED ENOUGH THAT AS STRONG WAVE CRASHES
INTO THE FLAT RIDGE ON WEDNESDAY NIGHT...INITIATING CYCLOGENESIS
TO THE WEST AND NORTH AND FORCES A STRONG COLD FRONT THROUGH THE
DAKOTAS...THIS FRONT SHOULD REMAIN LARGELY INERT OVERNIGHT AND
EVEN WELL INTO THURSDAY AS IT PUSHES INTO NORTHWEST IOWA BY
AFTERNOON. NAM REMAINS CONSISTENT WITH TRACK RECORD AS SLOWEST...
GFS FASTEST...AND OTHERS VARYING PACE BETWEEN. ONLY BY THURSDAY
AFTERNOON IN THE SOUTHEAST CWA AS MORE ORGANIZED AREA OF POST
FRONTAL Q VECTOR SUPPORT SWINGS OUT ACROSS THE BOUNDARY. SHOULD
GET A GOOD INCREASE IN PRECIPITATION ALONG AND POST FRONTAL DURING
THE EVENING...WHICH WILL THEN BUILD SOUTH AS STRONG LOW LEVEL
NORTHERLY DRYING WITH AGEOSTROPHIC SUPPORT OF JET ENTRANCE.

FOR THE MOST PART...HAVE LEFT THE REMAINING THREE DAYS OF THE
EXTENDED DRY AS SURFACE RIDGE TO THE NORTH WEDGES A GOOD DOSE OF
LOW LEVEL DRY AIR INTO THE REGION. SEVERAL SOLUTIONS ATTEMPT TO
BRING ANOTHER POST FRONTAL WAVE WITH A LITTLE MID LEVEL MOISTURE
POOLING AROUND THE START OF THE WEEKEND...BUT WITH MODELS
UNCERTAIN ON TIMING ON TOP OF THIS LOW LEVEL DRY AIR...DID NOT
MAKE SENSE TO ADD IN ANY LOWER CHANCE POPS AT THIS TIME. PERIOD OF
FRIDAY THROUGH SUNDAY WILL REMAIN COOL...WITH HIGHS IN THE UPPER
60S TO MID 70S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1232 PM CDT MON SEP 1 2014

FOCUS THIS SET OF TAFS WAS THE CONVECTION THAT IS EXPECTED TO
DEVELOP ACROSS WEST CENTRAL SOUTH DAKOTA THIS AFTERNOON...AND
SPREAD EAST OVERNIGHT. HAVE ADDED HIGH BASED SHOWERS TO THE
FORECAST..THOUGH LIMITED INSTABILITY MAY LEAD TO A RUMBLE OF
THUNDER OR TWO AT TAF SITES. WESTERLY FLOW PREVAILS THROUGH THE
PERIOD...GENERALLY REMAINLY AT OR BELOW 10 KNOTS.

&&

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

$$

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



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