000
FXUS63 KFSD 170953
AFDFSD

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

.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 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1032 PM CDT THU MAY 16 2013

EXPECT THUNDERSTORMS TO LINGER THROUGH 06Z OR 07Z AROUND I29 AND
AS TOWARD SUNRISE INTO PORTIONS OF SW MN. WITH THE BEST CHANCE FOR
CONVECTION EXPECTED TO BE IN THE VICINITY OF I90 INTO SW MN BY
06Z...ONLY HAVE MENTION OF SHOWERS IN THE KFSD TAF.
OTHERWISE...EXPECT THE CONVECTION TO KEEP THE SURFACE FRONT SOUTH
OF I90 INTO EARLY FRIDAY MORNING. WITH FRONT APPROACHING KFSD LATE
IN THE NIGHT...WOULD NOT BE SURPRISED TO SEE SOME LIGHT FOG
DEVELOP SO HAVE CONTINUED WITH 3-5 SM VSBYS WITH FOG LATER
TONIGHT. ALSO EXPECT SOME CIGS FROM 2000-3000 FT LATER TONIGHT
ALONG AND NORTH OF I90 DUE TO LIFT OVER THE WARM FRONT.

NO MODEL SEEMS TO HAVE A GOOD HANDLE ON THE WARM FRONT PROGRESSION
FRIDAY. THE 00Z NAM IS TOO FAST TONIGHT SINCE IT HAS NO CONVECTION
OVERNIGHT AND THE GFS APPEARS TOO SLOW GIVEN EXPECTED RISING
HEIGHTS TOMORROW WHICH SHOULD HELP THE FRONT MOVE TOWARD KHON AND
KMML DURING THE DAY. SO HAVE GONE BETWEEN THESE TO MODELS WITH
FROPA IN SIOUX FALLS MID TO LATE MORNING AND APPROACHING HURON
LATE AFTERNOON. ALTHOUGH THE FRONT WILL BE NEAR KHON LATE FRIDAY
AFTERNOON...THE LARGE SCALE RIDGING WILL REALLY TRY TO INHIBIT
CONVECTION SO WITH A LOW PROBABILITY DID NOT PUT INTO THE TAF LATE
TOMORROW AFTERNOON OR TOMORROW NIGHT. FARTHER SOUTH...WITH KFSD
AND KSUX SOUTH OF THE FRONT...DO NOT EXPECT CONVECTION TO DEVELOP
FRIDAY AFTERNOON OR EVENING.


&&

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

$$

SHORT TERM...CHAPMAN/
LONG TERM...
AVIATION...SCHUMACHER