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000
FXUS63 KFSD 120230
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
930 PM CDT TUE JUN 11 2013

.UPDATE...
ISSUED AT 929 PM CDT TUE JUN 11 2013

HAVE COORDINATED WITH SPC FOR A BIT OF A TONE DOWN TO THE SEVERE
WEATHER POTENTIAL. ISOLATED ACTIVITY WILL BE A THREAT IN THE NEAR
TERM...WHEN AN ACCAS TSRA DECIDES TO BREAK THROUGH THE CAP. BUT IT
IS CLOSE TO +15C AT 700MB... AND NAM ML CINS CONTINUE TO BE IN THE
300 TO 500 J/KG RANGE FROM ABOUT I 90 SOUTHWARD...RAPIDLY
DECREASING NORTH OF I 90 CREATING QUITE A CIN GRADIENT WHERE MANY
TIMES THUNDERSTORM COMPLEXES WILL TRAVEL. NOTING THAT THE ACTIVITY IN
THE NEBRASKA SAND HILLS HAS ALSO BEEN STRUGGLING SO FAR...NOT REAL
EXCITED ABOUT ANY CONVECTIVE EXPLOSION IN THE NEAR TERM BEFORE
MIDNIGHT NOTING THE CAP STRENGTH. SO ONE WONDERS IF WE WILL HAVE
TO WAIT FOR THE MAIN WAVE WHICH IS ACTIVE IN THE WESTERN PLAINS TO
ENCROACH IN ON OUR AREA...WHICH WOULD BE LATE TONIGHT AND EARLY
WEDNESDAY. WITH LESS CIN IN OUR NORTHERN ZONES...IT IS POSSIBLE
THE ACTIVITY WOULD BE MORE WIDESPREAD IN THOSE AREAS. SO FAR
NOW...BACKED OFF ON THE POPS IN THE EVENING HOURS...BUT STILL HAVE
NUMEROUS STORMS GOING OVER MANY AREAS EXCEPT OUR FAR SOUTHERN
ZONES LATE TONIGHT. OF COURSE...IF THE NEBRASKA SAND HILLS
CONVECTION BEGINS TO LIGHT UP...WILL RAMP UP THE POPS OVER OUR FAR
SOUTHERN ZONES TOO. BUT SO FAR THE NAM AND HRRR HAVE NOT BEEN
HANDLING THE CONVECTION VERY GOOD AND HAVE NOT BEEN GOOD GUIDANCE
TO FOLLOW...PREFERING THE 12Z ECMWF... GEM REGIONAL AND ARW. SO WE
WILL WAIT AND SEE...BUT AGREE SO FAR THAT THE HIGHEST WIND THREAT
MAY BE CONFINED TO OUR WESTERN ZONES GENERALLY FROM MITCHELL
WESTWARD IF THE ACTIVITY HAS TO MOVE IN FROM THE WEST...WITH ISOLATED
STRONG WIND GUSTS OR MICROBURSTS EAST OF MITCHELL. IF THE SEVERE
WEATHER THREAT WAITS UNTIL LATE TONIGHT...THE LARGE HAIL THREAT
WILL LIKELY BE MINIMAL...ALSO NOTING THAT THE ACTIVITY WILL BE
MULTICELLULAR BY THEN.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 413 PM CDT TUE JUN 11 2013

LINGERING ISOLATED HIGH BASED CONVECTION HAS JUST ABOUT ENDED THIS
AFTERNOON AS EXPECTED. WE WILL AWAIT THE SHORT WAVE AND THE HIGH
PROBABILITY OF STORMS AND EVENTUALLY A SYSTEM ASSOCIATED WITH IT.
WATER VAPOR IMAGERY SHOWS A STRONG UPPER LEVEL WAVE MOVING INTO
SOUTHWESTERN SOUTH DAKOTA. THE 18Z NAM SHOWS MLCIN ON THE ORDER OF
150 J/KG IN THIS AREA SO IT IS GOING TO TAKE A PERIOD OF LIFT WITHIN
THE CAP TO GET THUNDERSTORMS TO DEVELOP. THEREFORE NOT REALLY
EXPECTING THESE STORMS TO DEVELOP UNTIL CLOSER TO 00Z. THERE IS
AMPLE BULK SHEAR...AROUND 50 KTS IN THE 0 TO 6 KM LAYER...TO HELP
STORMS RAPIDLY ORGANIZE ONCE THEY DEVELOP.

THE QUESTION THEN BECOMES IF THE STORMS CAN BE MAINTAINED AS THE SUN
SETS AND SURFACE HEATING IS LOST. AT THIS POINT...IT APPEARS THE
STORMS SHOULD BE ABLE TO BE MAINTAINED DUE TO THE STRONG UPPER LEVEL
WAVE ENHANCING LIFT AHEAD OF THE LINE OF STORMS AND ACTING TO WEAKEN
THE CAP ENOUGH THAT SOME OF THE BOUNDARY LAYER AIR CAN BE UTILIZED
TO KEEP ROBUST UPDRAFTS DUE TO CAPES OVER 1000 J/KG. IN
ADDITION...IF THE STORMS ORGANIZE AND BEGIN TO GROW UPSCALE THEN
INTERNAL STORM DYNAMICS CAN HELP OVERCOME BOUNDARY LAYER
INHIBITION... SO A WELL ORGANIZED MCS SHOULD BE ABLE TO PROPAGATE
INTO EASTERN SOUTH DAKOTA. CURRENT HIGH RES MODELS...SUCH AS THE
HRRR...HAVE THESE STORMS IN THE VICINITY OF I90 IN WRN SD AFTER
DARK. FORWARD PROPAGATING CORFIDI VECTORS WOULD SUPPORT AN MCS
MOTION JUST NORTH OF EAST. THIS WOULD TAKE THE STORMS PRIMARILY
NORTH OF I90. AT THIS POINT...THIS APPEARS TO BE WHERE THE GREATEST
THREAT FOR SEVERE WEATHER WILL BE. ADDITIONAL DEVELOPMENT SOUTH OF
I90 IS POSSIBLE ON THE SOUTH SIDE OF THE SYSTEM. BUT WITH A STRONG
CAP...STORM MAY NOT EXTEND TOO FAR SOUTH OF I90. AS THE STORMS MOVE
EAST INTO MINNESOTA AND IOWA...THE INCREASING STABILITY LIKELY TO
WEAKEN CONVECTION OVERTIME AND DECREASE THE SEVERE THREAT AFTER 09Z.

AT THIS POINT...DAMAGING WINDS APPEAR TO BE THE GREATEST THREAT FOR
SEVERE WEATHER AS STORMS WILL LIKELY BE ORGANIZED INTO AN MCS BY THE
TIME THEY REACH THE MISSOURI RIVER. EXPECTATION IS STORMS WILL MOVE
TOWARD CHAMBERLAIN BETWEEN 04Z AND 08Z AND REACH I29 SOMETIME
BETWEEN 07Z AND 09Z. A FEW STORMS COULD PRODUCE QUARTER TO GOLF
BALLS SIZE HAIL OVERNIGHT ESPECIALLY ON THE SOUTH SIDE OF THE
COMPLEX WHERE NEW UPDRAFTS ARE MOST LIKELY AND CAN TAKE ADVANTAGE OF
LARGE CAPE IN THE HAIL PRODUCING LAYER...BUT THIS SHOULD NOT BE
WIDESPREAD AND IS A LOWER THREAT THAN WINDS.

WITH THE STRONG SOUTHERLY FLOW AND WINDS AND CLOUDS...LOWS WILL
REMAIN INTHE 60S OVERNIGHT WITH THE POSSIBILITY OF ONLY FALLING TO
70 DEGREES AROUND SIOUX CITY. THE AREA OF RAIN AND THUNDERSTORMS
WILL MOVE EAST OF THE AREA

THIS SYSTEM MAY PRESENT SOME TRAILING CELLS WEDNESDAY MORNING...BUT
AS A WHOLE...SHOULD STEADILY MOVE EAST OF OUR AREA GIVEN THE WELL
DEFINED NATURE OF THE WAVE. CLOUDS SHOULD DECREASE FROM THE
WEST/SOUTHWEST IN THE LATE MORNING AND AFTERNOON. A COOLER REGIME
WEDNESDAY SHOULD BRING HIGHS INT HE 70S TO LOWER 80S...WHICH ALLOWS
FOR SOME HEATING AS THE SYSTEM MOVES OUT AND LEAVES OUR AREA IN
COOLER AIR.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 413 PM CDT TUE JUN 11 2013

SHOULD SEE DECREASING CLOUDS WEDNESDAY NIGHT AND LIGHT WINDS...WITH
LARGE SCALE SUBSIDENCE BEHIND THE STRONG WAVE. LOWS WILL BE A BIT
COOLER...MAINLY IN THE 50S. MOSTLY SUNNY SKIES EXPECTED ON THURSDAY
WITH HIGHS AROUND AVERAGE FOR THIS TIME OF YEAR...UPPER 70S TO LOW
80S. BY THURSDAY NIGHT...LOW LEVEL JET AND THETAE ADVECTION BEGINS
TO INCREASE OVER THE REGION. THUS EXPECTING AN INCREASE IN MID LEVEL
CLOUDS WITH THE THREAT OF ISOLATED TO SCATTERED ELEVATED CONVECTION
THURSDAY NIGHT INTO FRIDAY. CURRENTLY THINKING SEVERE THREAT REMAINS
LOW WITH THE BEST INSTABILITY EXPECTED TO STAY TO OUR SOUTHWEST. BUT
WITH WIND FIELDS REMAINING UP...COULD SEE A FEW MARGINAL SEVERE
STORMS. A BETTER UPPER WAVE SHOULD ENTER THE NORTHERN PLAINS LATER
FRIDAY AFTERNOON INTO FRIDAY NIGHT. WITH CAPPING IN PLACE SURFACE
BASED CONVECTION DOES NOT SEEM LIKELY. BUT WITH CONTINUED LOW AND
MID LEVEL ISENTROPIC LIFT AND BETTER UPPER SUPPORT...THINKING IS WE
SEE AN INCREASE IN COVERAGE OF ELEVATED SHOWERS AND THUNDERSTORMS.
WITH HIGHER MUCAPE UP TO 2000 J/KG MAY SEE A SLIGHTLY BETTER CHANCE
OF SEVERE WEATHER FRIDAY NIGHT INTO SATURDAY MORNING. ALTHOUGH EVEN
THIS THREAT SEEMS PRETTY MARGINAL AND MAY END UP ACROSS OUR EASTERN
HALF OR EVEN EAST OF OUR CWA.

THE MORE ACTIVE PATTERN SHOULD END UP CONTINUING INTO THE WEEKEND
WITH HIGHS REMAINING NEAR OR JUST ABOVE AVERAGE...UPPER 70S TO MID
80S. CAP IS WEAKER ON SATURDAY WITH CAPE AROUND 2000 J/KG EXPECTED.
DRY AIR DOES WORK ITS WAY INTO THE AREA THOUGH...WHICH COMBINED WITH
THE WEAK CAP MAY PREVENT SURFACE BASED CONVECTION FROM
FORMING...ESPECIALLY WITHOUT A STRONG FORCING MECHANISM. WITH THAT
SAID WILL HAVE TO MONITOR AS IF SOMETHING CAN FORM...WIND FIELDS
SUGGEST A SUPERCELL POTENTIAL WITH LARGE HAIL AND STRONG WINDS.
LARGE SCALE FORCING INCREASES FOR SUNDAY WITH A WAVE PASSING TO OUR
NORTH. EC IS MUCH STRONGER WITH THIS WAVE AND WOULD SUGGEST A HIGHER
SEVERE THREAT. TIMING STILL UNCERTAIN ON THIS WAVE...SO TOUGH TO SAY
WHETHER BEST SHOT IS DURING THE AFTERNOON OR OVERNIGHT.

WENT DRY EARLY NEXT WEEK AS RIDGING BUILDS BACK INTO THE AREA. CANT
COMPLETELY RULE OUT AN ISOLATED SHOWER OR STORM...BUT THREAT SEEMS
TOO LOW TO MENTION IN THE FORECAST AT THIS TIME. GENERALLY EXPECTING
PARTLY TO MOSTLY SUNNY SKIES WITH HIGHS CONTINUING TO RUN WITHIN A
FEW DEGREES OF AVERAGE...MAYBE A BIT COOLER DEPENDING ON STRENGTH OF
THE WAVE SUNDAY INTO SUNDAY NIGHT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 626 PM CDT TUE JUN 11 2013

VFR CONDITIONS WITH GUSTY EAST WINDS THIS EVENING WILL GIVE WAY TO
A STRONG THUNDERSTORM COMPLEX MOVING WEST TO EAST ACROSS THE AREA
FROM AROUND MIDNIGHT THROUGH EARLY WEDNESDAY MORNING. THIS
THUNDERSTORMS COMPLEX IS EXPECTED TO BE SEVERE WITH THE MAIN
THREAT BEING STRONG/DAMAGING WINDS...MAINLY ON THE LEADING EDGE OF
THE COMPLEX AND NORTH OF INTERSTATE 90. LARGE HAIL TO GOLF BALL
SIZE WILL ALSO BE A POSSIBILITY. BEHIND THE DEPARTING
THUNDERSTORMS COMPLEX...VFR CONDITIONS WILL RESUME BY WEDNESDAY
MID MORNING...HOWEVER NORTH WINDS WILL BE GUSTY.


&&

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

$$

UPDATE...MJF
SHORT TERM...SCHUMACHER
LONG TERM...CHENARD
AVIATION...