Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 252051
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
351 PM CDT MON MAY 25 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 351 PM CDT MON MAY 25 2015

CONVECTIVE CONCERN IN THE IMMEDIATE TERM AT THE FOREFRONT FOR
AFTERNOON PACKAGE.  STRONG WAVE MOVING ACROSS CENTRAL AND NORTHERN
NEBRASKA AT THE PRESENT TIME...AND DRY SLOT HAS PUNCHED NORTHWARD
INTO MUCH OF THE CWA AT MID AFTERNOON. CLEARING SKIES HAVE DRIVEN
TEMPS UP INTO THE UPPER 70S IN THE SOUTHERN TIER...BUT SOME MIXING
OF THE MOISTURE KEEPING DEWPOINTS GENERALLY IN THE UPPER 50S. IN
PAST HOUR...THUNDERSTORMS STARTING TO DEVELOP ALONG A LINE FROM KFRM
TO NEAR PICKSTOWN.  FOR THE MOMENT...STORMS SHOWING A STRONG
PREFERENCE FOR MORE CONVERGENT AREAS OF THE WESTERN MISSOURI RIVER
VALLEY AT NOSE OF THE BETTER UPPER LEVEL FORCING...FIRING ON THE
GRADIENT OF THE INSTABILITY...WITH LESSER STORMS FURTHER EAST ALONG
THE MINNESOTA/IOWA BORDER WHERE CONVERGENCE IS WEAKER.  30 TO 35 KTS
SHEAR SUFFICIENT FOR ORGANIZED STRUCTURE...AND MLCAPE MAXIMIZING IN
A FAIRLY SKINNY PROFILE AROUND 1000 J/KG.  LIKELY THAT STORMS HAVE
SHOWN THEIR HAND AND WILL CONTINUE TO FAVOR THE INSTABILITY AND
CONVERGENCE BOUNDARY ALONG WHICH THEY HAVE ALIGNED...WHICH WILL TAKE
THE HIGHEST POPS FOR THE LATER AFTERNOON AND EVENING SOUTH OF A KMWM
TO KFSD TO PICKSTOWN LINE. MAIN SEVERE WEATHER THREAT WILL CONTINUE
THROUGH AROUND SUNSET...WITH BAND TRANSFORMING TOWARD MORE GENERAL
SHOWERS AND ISOLATED THUNDER.  WILL HAVE TO KEEP AN EYE ON
RAINFALL...AS STORMS WILL BE QUITE SLOW MOVING AND POTENTIALLY
TRAINING A BIT AS WELL AS THEY TRAVERSE ALONG THE BOUNDARY.

TRAILING UPPER ENERGY DRAGS ACROSS THE AREA ON TUESDAY...ESPECIALLY
NORTHWEST IOWA AND SOUTHWEST MINNESOTA. LOWER LEVEL BOUNDARY WILL
SLOW UP WITH WAVE MOVING UP LATE TONIGHT AND THROUGH THE MORNING TO
THE SOUTHEAST. LIKELY TO FIND DIURNALLY ENHANCED CU FIELD AS WELL AS
SOMETHING ON THE ORDER OF SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS. TREND WILL BE FOR DIURNAL SUPPORT TO INCREASE JUST AS
THE WAVE IS EXITING...SO WILL NEVER SEE THE MAXIMUM IMPACT IN OUR
CWA. WEAK FLOW...LOW CLOUD BASES...AND INSTABILITY SUGGEST THERE
COULD EVEN BE A THREAT FOR FUNNEL CLOUDS TOMORROW ACROSS THE
SOUTHEAST.  HIGHS WILL BE MAINLY UPPER 60S AND 70S...COOLEST WHERE
RAIN LINGERS THROUGH THE EARLY AFTERNOON.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 351 PM CDT MON MAY 25 2015

HIGH PRESSURE DRIFTS EAST ACROSS THE NORTHERN AND CENTRAL PLAINS ON
TUESDAY NIGHT AND WEDNESDAY. LIGHT WINDS AND MOSTLY CLEAR SKIES ARE
EXPECTED TUESDAY NIGHT WITH LOWS IN THE 50S. RETURN FLOW ON
DEVELOPING ON WEDNESDAY WILL SHIFT WINDS SOUTHERLY...LEADING TO A
PLEASANT LATE SPRING DAY. MOSTLY SUNNY TO PARTLY CLOUDY SKIES ARE
EXPECTED WITH HIGHS IN THE UPPER 70S AND LOWER 80S.

CLOUDS BEGIN BUILDING INTO THE AREA FROM THE WEST WEDNESDAY NIGHT
AHEAD OF A BROAD INTERMOUNTAIN WEST TROUGH DIGGING INTO THE FOUR
CORNERS REGION. THE LOW LEVEL JET NOSES INTO CENTRAL SOUTH DAKOTA
ALONG WITH A SUBTLE WAVE...WHICH SHOULD ALLOW THUNDERSTORM
DEVELOPMENT IN THE HIGH PLAINS AND INTO SOUTH CENTRAL SD - WEST OF
THE JAMES RIVER OVERNIGHT. THE DETAILS IN THE TIMING OF THESE WAVES
ARE STILL UNCERTAIN...BUT RIGHT NOW IT LOOKS LIKE THURSDAY WILL
POTENTIALLY SEE A BREAK IN THUNDERSTORM ACTIVITY IN THE MORNING AS
THE JET WANES WITH FURTHER DEVELOPMENT LATER IN THE DAY OR OVERNIGHT
THURSDAY NIGHT.

AS THE SLOW MOVING MAIN UPPER TROUGH BEGINS PUSHING INTO THE HIGH
PLAINS ON FRIDAY AND ACROSS THE PLAINS ON SATURDAY...THUNDERSTORM
CHANCES PERSIST. MODELS DIVERGE MORE SIGNIFICANTLY DURING THIS
PERIOD...SO UNCERTAINTY IN THE TIMING OF THE PRECIPITATION INCREASES
DURING THIS PERIOD. BY FRIDAY NIGHT...THE GFS AND ECMWF SHUNT MUCH
OF THE PRECIPITATION SOUTH AND EAST OF THE AREA...WHILE THE GEM
HANGS THE UPPER LOW NEAR THE FORECAST AREA INTO SATURDAY NIGHT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1214 PM CDT MON MAY 25 2015

MVFR CEILINGS CONTINUING TO RISE UP TOWARD LOWER VFR...WITH STRONG
CLEARING PUSH INTO KSUX AREA. SHOULD BE SOMEWHAT SELF DESTRUCTIVE
WITH VFR CUMULUS EXPECTED TO BUILD IN AREAS WHICH CLEAR TO THE
SOUTH. THUNDER MENTION WILL BE LIMITED TO KFSD AND KSUX...WITH
GREATEST IN THE LATTER. VERY SLOW MOVING BOUNDARY AND LINGERING
LOWER LEVEL MOISTURE COULD PRODUCE ANOTHER IFR FOG/STRATUS EPISODE
FOR MAINLY THE KSUX AREA LATER TONIGHT.

&&

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

$$

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


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