Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 290507
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1207 AM CDT FRI AUG 29 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 335 PM CDT THU AUG 28 2014

MAIN CONCERN ARE CONTINUED RAIN CHANCES AS THE UPPER LOW CONTINUES
TO SLOWLY MOVE EAST.

A STRONG DRY SLOT MOVED THROUGH MOST OF EASTERN SD...WESTERN IOWA
AND SOUTHWEST MN LATE THIS MORNING. WITH SOME HEATING OVER ERN
NEBRASKA...THERE IS SOME WEAK INSTABILITY DEVELOPING SUCH THAT
SCATTERED SHOWERS MAY DEVELOP DURING THE EVENING EAST OF VERMILLION
TO MML LINE. ANOTHER AREA OF THUNDERSTORMS HAVE BEEN DEVELOPING THIS
AFTERNOON WEST OF THE JAMES RIVER. EXPECT THAT STORMS WILL CONTINUE
TO DEVELOP THROUGH THE EVENING. THERE HAS BEEN A LITTLE MORE HEATING
AND THE PROXIMITY OF THE UPPER LEVEL WAVE SHOULD HELP ENHANCE THE
ASCENT AND DEVELOPMENT THROUGH 00Z OR SO. HOWEVER...AS THE
SUNSET...INSTABILITY WILL DECREASE AND SHOULD RESULT IN A GRADUAL
DECREASE IN SHOWERS AND STORMS...ALTHOUGH CANNOT RULE A STORM
TOWARD I29 THROUGH THE NIGHT AS THE UPPER LOW CONTINUES EAST.

THE OTHER CONCERN TONIGHT IS FOG POTENTIAL. WINDS WILL BE LIGHT OVER
THE JAMES AND MISSOURI VALLEY LATER TONIGHT AS THE SFC TROUGH SLOWLY
MOVES TO THE EAST. WITH RAIN EARLIER TODAY...THIS SETS UP A HIGH
POTENTIAL FOR FOG AFTER MIDNIGHT AND INTO FRIDAY MORNING. WITH A
SLOW INCREASE IN NW FLOW TOMORROW MORNING AS THE TROUGH MOVES TOWARD
I29...HAVE THE FOG DISSIPATE BY MID MORNING. WITH THE FLOW
CONTINUING TO BE WEAK...THIS FOG COULD PERSIST LATER INTO THE NIGHT.
THE OTHER EFFECT OF THE LOW LEVEL MOISTURE IS THAT LOWS WILL BE
WARMER TONIGHT FROM THE LOWER 60S AROUND KHON TO THE UPPER 60S
AROUND KSUX.

THE UPPER LOW WILL SLOWLY MOVE EAST THROUGH FRIDAY MORNING...
REACHING ERN NEBRASKA AROUND 18Z. WITH THE STRONG FORCING FOR ASCENT
COMBINED WITH LOW LEVEL INSTABILITY...EXPECT THAT SHOWERS WILL BEGIN
TO DEVELOP BY LATE MORNING NEAR THE MISSOURI RIVER AND SPREAD
NORTHEAST THROUGH THE AFTERNOON. WITH THE SLOWER MOVEMENT OF THE
UPPER LOW HAVE RAISED PRECIPITATION CHANCES OVER MOST SW MN AND NW
IA...WITH AREAS FROM SUX TO MJQ HAVING THE GREATEST CHANCE FOR RAIN.
IN GENERAL...EXPECTING FROM A TENTH TO HALF INCH OF RAIN IN THIS
AREA...WITH LESS TO NORTHWEST...BUT COULD SEE LOCAL AMOUNTS UP TO AN
INCH WITH STRONGER STORMS. FARTHER WEST...SKIES SHOULD CLEAR THROUGH
THE DAY. WITH THE LACK OF COLD ADVECTION...TEMPERATURES SHOULD RISE
INTO THE 80S...WITH MID 80S WEST OF THE JAMES RIVER. WITH MORE
CLOUDS AND PRECIPITATION...IT WILL REMAIN IN THE MID TO UPPER 70S
EAST OF THE JAMES RIVER.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 335 PM CDT THU AUG 28 2014

LINGERING TSRA ARE EXPECTED ON FRIDAY NIGHT AS THE TROUGH AND
ASSOCIATED SFC FRONT CONTINUES TO MOVE THROUGH THE CWA. AFTER
FROPA...SKIES WILL CLEAR SOME ALLOWING FOR TEMPS TO WARM BACK INTO
THE LOWER 80S.

SUNDAY STILL LOOKS LIKE A POTENTIAL SEVERE WX DAY. LLVL JET IS
AROUND 40-45KTS ADVECTING A STRONG THERMAL GRADIENT INTO SE SOUTH
DAKOTA. DECENT AMT OF SHEAR IS ALSO PRESENT ESPECIALLY IN THE
AFTERNOON. LIMITING FACTOR WILL BE SKY COVER WHICH WILL LIMIT THE
AMT OF INSOLATION TO CORRESPOND WITH BETTER SVR PARAMETERS AS WELL
AS SOMEWHAT OF A CAP. EITHER WAY...STRENGTH OF APPROACHING WAVE
AND RESULTANT SFC FRONT MAY BE ABLE TO OVERCOME THIS...ESPECIALLY
LATER IN THE EVENING HOURS. THE FRONT SHOULD CLEAR THE CWA BY
MONDAY MORNING.

ZONAL FLOW SETS UP FOR MON NIGHT INTO TUES WITH A WEAK WAVEQUICKLY
PASSING THROUGH ON MONDAY NIGHT BRINGING A LOW CHANCE OF TSRA.

FOR TUES THROUGH THURS...ONLY CHANCE OF TSRA DURING THIS PD IS IN
SOUTHWEST MN ON TUES NIGHT AND MOST OF THE CWA ON WED NIGHT AS
YET ANOTHER FEW WEAK WAVES PASS THROUGH BRINGING A LOW CHANCE OF
TSRA.

TEMPS THROUGH THE PD ARE EXPECTED TO BE AT OR SLIGHTLY BELOW
NORMAL FOR THIS TIME OF YEAR.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1205 AM CDT FRI AUG 29 2014

PLENTY OF CHALLENGES FOR THE 06Z TAFS. THE KFSD TAF HAS BEEN
PROBLEMATIC ALL EVENING...IN THAT THE SITE HAS BEEN ON THE EDGE OF
LOWER END VFR...AND LIFR WHICH IS VERY WIDESPREAD IN SOUTHWEST MN.
THE NEAR SURFACE WINDS HAVE BEEN OUT OF THE EAST USHERING IN THE
LIFR/IFR CONDITIONS FROM MN. HOWEVER SOME INDICATIONS NOW EXIST
THAT THE NEAR SURFACE WINDS WILL...AND IN FACT ARE...SHIFTING TO
THE SOUTHEAST. THAT COULD MAKE A WORLD OF DIFFERENCE FOR THE CLOUD
CATEGORY FOR SIOUX FALLS AS NORTHWEST IA IS CURRENTLY LOWER END
VFR. FOR NOW...HEDGED THE KFSD TAF FOR THE NEAR TERM IN THE MVFR
RANGE AND NOT IFR/LIFR. WILL HAVE TO AMEND IF IFR CEILINGS
STUBBORNLY HANG ON. AT ANY RATE...LIFR CONDITIONS ARE LIKELY TO
PREVAIL NEAR SUNRISE AS VERY MOIST AIR TRANSLATES INTO LOW
VISIBILITIES AND CEILINGS AT THAT TIME. SOUNDINGS SHOW A DEGREE OF
DECENT MIX OUT RAISING THE CEILINGS BY FRIDAY MIDDAY INTO THE
LOWER END VFR RANGE.

LIFR AND IFR ARE ALSO LIKELY TO PREVAIL AT KHON FOR THE REST OF
TONIGHT AND INTO FRIDAY MORNING. KEPT THE VISIBILITIES NEAR
SUNRISE A LITTLE MORE OPTIMISTIC WHEN COMPARED TO KFSD...BUT
CEILINGS ARE LIKELY TO BE LIFR ANYWAY. KHON SHOULD GO VFR BY
FRIDAY AFTERNOON SIMILAR TO KFSD...BUT THEN A WIND SHIFT/WEAK COLD
FRONT MAY USHER IN SOME SHOWERS AND A FEW STORMS FRIDAY EVENING.

KSUX WILL BE VFR IN THE NEAR TERM...BUT AGAIN AM WORRIED WITH THE
AMPLE SURFACE MOISTURE AND WET GROUND...THAT IFR/LIFR COULD
DEVELOP AT THIS SITE ALSO AROUND SUNRISE. SIMILAR TO KFSD AND
KHON...MODEL SOUNDINGS SHOW MIXING INTO THE LOWER END VFR CATEGORY
BY MIDDAY FRIDAY.

LEFT OUT THE MENTION OF THUNDERSTORMS IN THE TAF SITES FOR THE
REST OF TONIGHT...ONLY SHOWERS. LIGHTNING HAS BEEN PRETTY SPARSE
IN THIS AREA.

&&

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

$$

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


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