Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 040828
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
328 AM CDT FRI SEP 4 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 328 AM CDT FRI SEP 4 2015

WELL DEFINED SHORT WAVE MOVING NORTHEAST OVER WESTERN AND NORTHERN
SOUTH DAKOTA TODAY IS PROVIDING A GOOD FOCUS FOR SCATTERED SHOWERS
AND STORMS SPREADING MOVING ACROSS THE WEST AND NORTH PARTS OF OUR
FORECAST AREA. DESPITE SOME MOISTURE AND DECENT INSTABILITY OVER THE
AREA...THERE DOES NOT SEEM TO BE MUCH OTHER REASON FOR CONVECTION TO
INITIATE. SHORT TERM/HI RESOLUTION MODELS HAVE BEEN DEPICTING A FEW
SHOWERS AND STORMS MOVING ACROSS NORTHWEST IOWA DURING THE DAY. THIS
APPEARS AT LEAST OVERDONE AND IN VIEW OF PAST PERFORMANCE OF THESE
MODELS...WOULD NOT DISCARD THE MEAGER NATURE OF THE UPPER SUPPORT
AWAY FROM THE SHORT WAVE...AND SOME DEGREE OF CAPPING. IT IS
POSSIBLE THESE MODELS MAY BE ACTING ON MID LEVEL INSTABILITY AND
MOISTURE AND WILL ALLOW SMALL MENTION POPS INTO OUR EXTREME
NORTHEAST NEBRASKA COUNTIES LATER THIS MORNING...THEN PUT A SLIGHT
CHANCE OVER THE EASTERN BORDER OF OUR CWA FOR THIS AFTERNOON. ANY
ACTIVITY THIS MORNING SHOULD BE PRETTY WEAK. SMALL POPS IN SOUTHWEST
MINNESOTA THIS AFTERNOON FIT WITH THE SPC MARGINAL SEVERE RISK BUT
CERTAINLY WOULD NOT GET TOO EXCITED. MOST OF THE CONVECTION TODAY
SHOULD HUG THE UPPER SUPPORT.

TEMPERATURES ARE NOT TOO DIFFICULT AND SHOULD BE SIMILAR TO
THURSDAY...HIGHS IN THE MID 80S TO LOWER 90S. DEW POINTS WITH THE
HUMID CONDITIONS WILL BE SIMILAR AS WELL. WINDS MAY GET BRIEFLY
BREEZY IN PART OF THE AREA. THE HEAT INDEX WILL REACH THE 90S...SOME
UPPER 90S BRIEFLY SOUTHWEST...BUT STAY BELOW THE HEAT ADVISORY LEVEL.

TONIGHT THE LINGERING SHOWER SAND STORMS NORTH SHOULD GRADUALLY WANE
AS THE WAVE MOVES OFF TO THE NORTHEAST. WILL KEEP A MODEST INCREASE
IN POPS OVER THE AREA TOWARD THE END OF TONIGHT AS MODELS CONTINUE
TO INDICATE SOME ILL DEFINES AND WEAK UPPER AND THERMAL SUPPORT. A
LITTLE BETTER BREEZE SHOULD HOLD UP DURING THE NIGHT AND HELP KEEP
TEMPERATURES FROM DIPPING BELOW 70 ANYWHERE.


.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 328 AM CDT FRI SEP 4 2015

SATURDAY IS A REAL QUESTION MARK...WITH LOW CONFIDENCE FORECASTING
ON EXACT TIMING AND PLACEMENT OF TSRA CHANCES. STRONG UPPER LOW IS
SITUATED OVER THE PACIFIC NORTHWEST...USHERING IN AN UNSTABLE
SOUTHWEST FLOW ALOFT THROUGHOUT THE FRONT RANGE AND PLAINS STATES.
SATURDAY MORNING...THERE DOES NOT APPEAR TO BE A VERY DEFINED FOCUS
FOR CONVECTIVE ACTIVITY WITH ONLY A DECENT LOW LEVEL JET OF 30 KNOTS
IN THIS AREA PROVIDING A BIT OF ASCENT. THEREFORE ONLY VERY LOW POPS
ARE WARRANTED SATURDAY MORNING. IN THE AFTERNOON...IT IS POSSIBLE
THAT SCATTERED THUNDERSTORMS COULD DEVELOP...ESPECIALLY FOR AREAS
OTHER THAN NORTHWEST IOWA...AS HEATING INCREASES WITH A VERY
HUMID...BUOYANT AIR MASS. THE ONE WILDCARD IS THE HEATING ITSELF.
BOTH THE GFS AND NAM SHOW A LOT OF MID CLOUDS IN THE 700 TO 500MB
LAYER. IF THE CLOUD COVER IS THICK ENOUGH...HIGH TEMPERATURES MAY
NOT BE REALIZED ADDING TO STABILITY.

THIS CHANGES SATURDAY NIGHT AS THE VARIOUS MODELS ARE IN PRETTY GOOD
AGREEMENT IN BRINGING A SHORT WAVE THROUGH WITH SUBTLE MID LEVEL
HEIGHT FALLS. THE LOW LEVEL JET ALSO INCREASES TO 35 TO 45 KNOTS.
LIKELY POPS ARE WARRANTED FOR MUCH OF THE FORECAST AREA...MINUS OUR
FAR WESTERN ZONES WHERE THE SHORT WAVE MOVES THROUGH TOO FAST...AND
OUR FAR SOUTHEAST ZONES...ENCOMPASSING MOST OF NORTHWEST IOWA...
WHERE THE SHORT WAVE MAY BE TOO FAR WEST.

ON SUNDAY...AS THE UPPER LOW TRACKS NORTHEASTWARD INTO SOUTHWEST
CANADA AND THE AFOREMENTIONED SHORT WAVE EXITS...A SURFACE WIND
SHIFT MOVES ACROSS THE WESTERN HALF OF OUR AREA. BLENDED DIFFERING
MODEL SOLUTIONS FOR THE WIND SHIFT TIMING AS THERE WAS SOME PRETTY
DECENT DISCREPANCIES. BUT IN GENERAL...THE FRONT REMAINS WEST OF
NORTHWEST IOWA AND SOUTHWEST MINNESOTA GIVING THOSE LOCATIONS GOOD
CHANCES FOR STORMS ON SUNDAY...LINGERING IN OUR FAR EAST SUNDAY
EVENING JUST AHEAD OF THE WIND SHIFT. SATURDAY NIGHT WILL BE VERY
WARM WITH A STOUT SOUTHERLY FLOW IN PLACE...FOLLOWED BY ANOTHER VERY
WARM DAY ON SUNDAY. BUT WITH THE WIND SHIFT MOVING THROUGH...DEW
POINT VALUES WILL BE DROPPING ALONG AND WEST OF THE JAMES RIVER
VALLEY...WITH ANOTHER VERY HUMID DAY EAST OF THE JAMES. WITH
DIFFERENT ACTIVITIES GOING ON THIS LABOR DAY WEEKEND...WILL MENTION
HEAT INDEX VALUES IN THE FORTHCOMING HWO.

CONCERNING TEMPERATURES...SATURDAY STILL LOOKS VERY WARM AND HUMID.
BOOSTED SUPERBLEND DEW POINTS AS THEY HAVE BEEN RUNNING A FEW
DEGREES TOO COOL EACH DAY...AND SEE NO REASON FOR THAT TO CHANGE ON
SATURDAY. DESPITE ABUNDANT MID CLOUDS...AM CONFIDENT THAT HIGHS WILL
BE IN THE 80S ON SATURDAY...LOWER 90S IN SOUTH CENTRAL SD. THESE
HIGHS GET REALIZED BY NOT MIXING TO 850MB. IF MORE SUN BREAKS OUT
THAN ANTICIPATED AND MIXING TO 850MB OCCURS...THEN MORE LOWER 90S
WILL TAKE PLACE.

FURTHER OUT BEGINNING ON MONDAY...THE VARIOUS MODELS ARE SIMILAR IN
SHOWING A STRONG...CLOSED UPPER LOW SITUATED ALONG THE SASKATCHEWAN
AND MANITOBA BORDER IN SOUTH CENTRAL CANADA. THE LOW THEN MOVES INTO
CENTRAL MANITOBA DURING THE DAY...MOVING SLIGHTLY EASTWARD MONDAY
NIGHT TOWARD THE ONTARIO BORDER. IN RESPONSE...SURFACE LOW PRESSURE
DEVELOPS OVER THE SOUTHWESTERN HIGH PLAINS ON MONDAY...THEN
ELONGATES NORTHEAST TO SOUTHWEST AND MORPHS INTO A WELL DEFINED
FRONTAL BOUNDARY MONDAY NIGHT THROUGHOUT THE CENTRAL PLAINS. THE
ECMWF IS THE FURTHEST SOUTH WITH THIS BOUNDARY AND PLACES A
NORTHERLY FLOW OF SURFACE AIR THROUGHOUT OUR ENTIRE FORECAST AREA BY
12Z TUESDAY. THIS SOLUTION IS NOT SUPPORTED BY THE GEM GLOBAL AND
GFS...WHO ARE SIMILAR IN PUTTING THE WIND SHIFT ALONG AN AXIS JUST
BEHIND AN INVERTED TROUGH SQUARELY IN NORTHWEST IOWA. THEREFORE
SHOWERS WITH POSSIBLE EMBEDDED THUNDERSTORMS ARE QUITE POSSIBLE
MONDAY NIGHT...WITH THOSE TWO MODELS KEEPING SOME SKITTISH CHANCES
FOR SHOWERS AROUND ON TUESDAY AS COOL AIR BEGINS TO FILTER IN.

THE MIDDLE OF THE WEEK LOOKS DRY WITH A NORTHWEST FLOW ALOFT AND
STABLE HIGH PRESSURE IN FIRM CONTROL FOR A FEW DAYS...ONCE AGAIN
FAVORING THE GEM GLOBAL AND GFS WHICH HANDLE THE MOVEMENT EASTWARD
OF THE LARGE HIGH ACROSS THE PLAINS VERY SIMILARLY. TEMPERATURES
LOOK A BIT BELOW NORMAL WEDNESDAY AND THURSDAY...BUT SHOULD BE VERY
PLEASANT DAYS.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1025 PM CDT THU SEP 3 2015

VFR THROUGH THE PERIOD. ISOLATED THUNDERSTORMS WILL BE POSSIBLE ON
FRIDAY BUT LOCATION AND TIMING ARE DIFFICULT TO PIN DOWN. THE
BETTER CHANCES WILL BE CLOSER TO KHON LATE FRIDAY MORNING INTO THE
AFTERNOON. SURFACE SOUTHERLY WINDS SHOULD GUST OVER 25 MPH AT
TIMES THROUGH THE DAY.


&&

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

$$

SHORT TERM...
LONG TERM...MJ
AVIATION...08



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