588 
FXUS63 KFSD 171600
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1100 AM CDT FRI MAY 17 2013

.UPDATE...
ISSUED AT 1050 AM CDT FRI MAY 17 2013

NO MAJOR CHANGES TO THE FORECAST THROUGH THE AFTERNOON. CLOUDS
DECREASING A BIT MORE THAN ANTICIPATED SO BRINGING IN A LITTLE
MORE SUNSHINE FOR THE DAY. DID INCREASE CLOUD COVER MORE QUICKLY
THIS EVENING IN CENTRAL SD AS CONVECTION FAIRLY LIKELY TO FIRE
BETWEEN ABOUT 23Z AND 3Z JUST TO THE WEST AND SOUTHWEST OF THE
CWA. ALL HIGH RESOLUTION MODELS AS WELL AS THE NAM AND GEM SUPPORT
CONVECTIVE INITIATION FROM SOMEWHERE BETWEEN ABOUT CHADRON AND
VALENTINE NEBRASKA NORTH TOWARDS PIERRE DURING THIS TIME. EXPECT
THIS ACTIVITY TO MOVE NORTHEAST THROUGH THE EVENING THEN POSSIBLY
TRACK THROUGH THE FAR WESTERN AND NORTHERN CWA OVERNIGHT. MAY NEED
TO ADD SOME SMALL POPS INTO AREAS ALONG AND NORTH OF INTERSTATE 90
AS UPPER LEVEL SUPPORT SWINGS THROUGH AND WITH A LITTLE ELEVATED
INSTABILITY COULD SEE SOME SPOTTY SHOWERS OR THUNDERSTORMS
DEVELOP. SEVERE THUNDERSTORMS VERY UNLIKELY BUT A FEW COULD GET
CLOSE AROUND THE CHAMBERLAIN AREA THIS EVENING. CAPE VALUES LIKELY
AROUND 1500 J/KG WITH ONLY MARGINAL EFFECTIVE SHEAR BUT STILL
ENOUGH TO SUPPORT A WIND OR HAIL THREAT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 453 AM CDT FRI MAY 17 2013

MAIN ACTION FROM THE EVENING AND EARLIER OVERNIGHT HAS SHIFTED EAST 
OF THE AREA WITH DYNAMICS OF MAIN WAVE PUSHING ACROSS MINNESOTA AND 
IOWA. CONVECTIVELY REINFORCED FRONTAL BOUNDARY LIES JUST SOUTH OF 
THE AREA ACROSS EASTERN NEBRASKA. HOWEVER...A VERY NICE COHERENT 
CYCLONICALLY WRAPPED CORE OF RETURNS NOTED MOVING ACROSS THE WESTERN 
CWA BETWEEN I 90 AND THE MISSOURI RIVER...ASSOCIATED WITH AN MCV 
FROM EARLIER HIGH PLAINS CONVECTION. TWO THINGS WORKING AGAINST THIS 
PRECIP ARE THE INCREASING VEERING OF LOW LEVEL JET AWAY FROM SLOW 
MOVING AREA OF PRECIPITATION...AND ALSO THE LARGE SCALE FORCING 
BECOMING MORE HOSTILE WITH HEIGHTS BEGINNING TO BUILD ALOFT. LIKELY 
TO SEE OVERALL COVERAGE WITH THIS CORE DECREASE HEADING INTO THE 
EARLY MORNING HOURS AS IT SHIFTS EAST...BUT HOW QUICKLY THIS OCCURS 
IS THE QUESTION. WOULD THINK AT LEAST SOME OF THIS WOULD LIMP INTO 
THE FSD AREA AFTER 12Z...WITH SOME INDICATION THAT BROADER AREA MAY 
REDEVELOP FOR A SHORT TIME AHEAD OF THIS FEATURE FROM SOUTHWEST 
MINNESOTA INTO FAR NORTHERN IOWA. CHANCES FOR PRECIP SHOULD REALLY
DIMINISH AFTER 15Z...AND DESPITE A MARGINALLY UNSTABLE AIRMASS 
ALOFT...KEPT MENTION OF THUNDER AT LEAST A CATEGORY OR TWO UNDER 
EXPECTED PRECIP COVERAGE. FOR MUCH OF THE AFTERNOON...EXPECT VERY 
LITTLE TO OCCUR AS WARM FRONT CONTINUES TO PUSH NORTHWARD...WITH 
HEIGHTS BUILDING/TEMPS WARMING ALOFT. 

WHILE SOME LINGERING CLOUDS AND DEVELOPMENT OF CAPPED CUMULUS FIELD  
WILL BE A DISTINCT ISSUE FOR NORTHERN/EASTERN CWA...IS FAIRLY LIKELY 
THAT THE FAR SOUTHWEST WILL BREAK INTO A GREATER DEGREE OF SUNSHINE 
TODAY.  WINDS WILL MAINTAIN TOO MUCH OF A SOUTH OR SOUTHEAST 
COMPONENT TO EXPECT TEMPS TO FULLY RACE ABOVE GUIDANCE...BUT PURE 
MIXING OF RAW MODEL OFF SURFACE TEMPS WOULD SUGGEST UPPER 80S A GOOD 
BET FOR THE SOUTHWEST...SLIDING TOWARD MORE UPPER 70S TO LOWER 80S 
FROM EAST CENTRAL SD THROUGH SOUTHWEST MINNESOTA.

WILL KEEP A SMALL POP IN OUR FAR NORTH...MAINLY ALONG THE HIGHWAY 14
CORRIDOR THIS EVENING...WITH SURFACE BOUNDARY EXPECTED TO BE IN THAT
VICINITY AS SUBTLE WAVE IS FORECAST TO LIFT INTO CENTRAL SD. SOME
UNCERTAINTY REGARDING LOCATION OF THE LOW LEVEL BOUNDARY BY THIS
EVENING...AND ANY CHANGE IN LOCATION WOULD IMPACT THE EVENING POPS.
WAVE AND ASSOCIATED LOW LEVEL WARM ADVECTION EXPECTED TO SHIFT NORTH
OF THE AREA AFTER 06Z...AND THUS TAPER POPS OFF THROUGH THE LATTER
HALF OF THE NIGHT. SHOULD BE A MILD NIGHT WITH LOWS IN THE LOWER 60S
MOST AREAS.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 453 AM CDT FRI MAY 17 2013

MAIN FOCUS IN THE LONGER TERM IS CONVECTIVE DEVELOPMENT/ASSOCIATED
SEVERE THREAT OVER THE WEEKEND AS WESTERN CONUS TROUGH PUSHES OUT
INTO THE PLAINS. EXPECT MOST OF SATURDAY TO BE CAPPED OFF...WITH
SURFACE BOUNDARY EXTENDING FROM WESTERN NEBRASKA THROUGH CENTRAL
SOUTH DAKOTA...AND THEN NORTHEAST INTO FAR SOUTHEAST NORTH DAKOTA.
OUR FORECAST AREA WELL INTO THE WARM SECTOR AND FORECAST SOUNDINGS
SUGGEST STRONG CAP IN PLACE THAT SHOULD INHIBIT DEVELOPMENT WITHOUT
ASSISTANCE FROM DYNAMIC FORCING. WILL KEEP A SLIGHT CHANCE IN OUR
FAR WEST IN THE AFTERNOON...BUT PREFER 17/00Z GFS AND 16/12Z ECMWF
PLACEMENT OF INITIAL DEVELOPMENT MAINLY WEST OF OUR AREA NEAR THE
BOUNDARY THROUGH THE LATE AFTERNOON. WITHIN THE WARM SECTOR...WILL
SEE A HOT/HUMID DAY WITH HIGHS IN THE MID-UPPER 80S AND AFTERNOON
DEW POINTS IN THE LOWER TO MID 60S.

ACTIVITY SHOULD QUICKLY DEVELOP INTO OUR WEST SATURDAY EVENING AS
MID-UPPER WAVE LIFTS INTO CENTRAL SOUTH DAKOTA AND AIDS IN BREAKING
THE STRONG CAP. DEEP LAYER SHEAR SOMEWHAT MARGINAL INITIALLY THIS FAR
EAST ALTHOUGH STRONG DYNAMIC LIFT ALONG WITH STEEP MID LEVEL LAPSE
RATES AND INSTABILITY IN THE 2000-3000 J/KG RANGE SUPPORTIVE OF A
SIGNIFICANT HAIL THREAT WITH INITIAL DEVELOPMENT ACROSS FAR WESTERN
CWA SATURDAY EVENING. ISOLATED TORNADO THREAT AS WELL...BUT THINK
THIS WILL BE TIED MORE CLOSELY TO THE BOUNDARY...WITH WIND THREAT
INCREASING AS THE STORMS MOVE EAST THROUGH SOUTHEAST SOUTH DAKOTA IN
THE LATE EVENING. 

SUNDAY LESS CLEAR AS WILL BE DEPENDENT ON EVOLUTION OF ACTIVITY LATE
SATURDAY NIGHT/SUNDAY MORNING. CURRENT EXPECTATION WOULD SEE STORMS
PUSH EAST OF THE AREA EARLY SUNDAY MORNING...WITH PARTIAL CLEARING IN
THE EAST BY MIDDAY AS MID LEVEL DRY SLOT MOVES IN EAST OF UPPER LOW
AS IT BEGINS TO CLOSE OFF OVER CENTRAL PORTIONS OF SOUTH DAKOTA AND
NEBRASKA. WILL HANG ONTO CHANCE POPS IN MOST AREAS SUNDAY MORNING
GIVEN GREAT DEAL OF UNCERTAINTY IN THIS EVOLUTION. WAVE SWINGING
THROUGH THE BASE OF THE CLOSED LOW SHOULD THEN BRING INCREASING
THREAT OF DEVELOPMENT THROUGH THE AFTERNOON...WITH GFS INDICATING
POTENTIAL FOR ANOTHER ROUND OF SEVERE STORMS IN OUR CENTRAL/EASTERN
CWA...WITH WEAK CAP TOPPED BY STEEP LAPSE RATES/STRONG INSTABILITY
AND SLIGHTLY BETTER DEEP LAYER SHEAR THAN IN OUR WEST ON SATURDAY.
OTHER MODELS NOT QUITE AS BULLISH ON INSTABILITY ACROSS THE EAST
SUNDAY AFTERNOON...THOUGH STILL PLENTY OF DYNAMICS WITH UPPER LEVEL
SUPPORT TO ASSIST DEVELOPMENT AND AT LEAST ISOLATED SEVERE THREAT.

CLOSED UPPER LOW SLOW TO SHIFT EAST OF THE AREA...KEEPING DECENT
CHANCE OF SHOWERS AROUND THROUGH TUESDAY NIGHT BEFORE INFLUENCE
BEGINS TO WEAKEN. MID-UPPER LEVEL RIDGING SHOULD BRING DRIER WEATHER
TO THE AREA BY WEDNESDAY NIGHT/THURSDAY...THOUGH TEMPERATURES WILL BE
ON THE COOL SIDE OF NORMAL MIDWEEK WITH HIGHS MAINLY IN THE 60S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 705 AM CDT FRI MAY 17 2013

LOW LEVEL MOISTURE WILL PROVIDE THE GREATEST CHALLENGE TO THE
AVIATION PACKAGE THIS MORNING...WITH THE MAIN QUESTIONS
SURROUNDING THE DEVELOPMENT OF LOWER CLOUDS AND FOG THROUGH THE
PERIOD. AREAS OF MVFR VISIBILITIES/LIFR CEILINGS HAVE DEVELOPED
NORTH OF A WARM FRONT NEAR THE MISSOURI RIVER VALLEY...GENERALLY
WHERE SKIES HAVE PARTIALLY CLEARED BEHIND EXITING WEAK SHOWERS.
WILL LIKELY SEE DEVELOPMENT OF A BRIEF PERIOD OF MVFR CEILINGS
WITH DAYTIME HEATING NORTH OF THE WARM FRONT...THEN BREAKING TO
VFR CONDITIONS FOR MUCH OF THE REMAINDER OF THE TIME. AFTER A DAY
OF INCREASING SOUTHERLY FLOW AND STABILIZING TEMPERATURES ALOFT...
QUITE PROBABLE THAT THE FAIRLY WIDESPREAD STRATUS AND LOW
VISIBILITIES THROUGH THE SOUTHERN PLAINS MAY PLAGUE OUR TAF SITES
BY EARLY SATURDAY MORNING. MAY NOT ADVECT FAR ENOUGH NORTH TO
IMPACT KHON...BUT DID INTRODUCE LATE AT NIGHT FOR KFSD AND KSUX.


&&

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

$$

UPDATE...08
SHORT TERM...CHAPMAN/
LONG TERM...
AVIATION...CHAPMAN