000
FXUS63 KFSD 121008
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
508 AM CDT WED JUN 12 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 508 AM CDT WED JUN 12 2013

TWO MAIN AREAS OF CONVECTION PRESENTLY ONGOING ACROSS THE CWA VERY
EARLY THIS MORNING. THE FIRST IS LOCATED THROUGH OUR SOUTHEASTERN
ZONES IN CONJUNCTION WITH A LEADING SHORTWAVE AHEAD OF MAIN WAVE...
WHERE CONVERGENCE ON THE NOSE OF THE LOW LEVEL JET IS MAXIMIZED.
THESE STORMS HAVE REMAINED TAME THROUGHOUT THE NIGHT WITH CAPPING
REMAINING ACROSS THE AREA. SECOND AREA OF CONVECTION POISED TO ENTER
OUR NORTHWESTERN ZONES OVER THE NEXT HOUR OR SO...THIS IN A FORM OF
LINE WHICH HAS BEEN MARCHING ACROSS SOUTH DAKOTA THROUGH THE NIGHT
AS THE MAIN WAVE TRACKS EASTWARD. THE SOUTHERN PORTION OF THE LINE
HAS WEAKENED THROUGH THE NIGHT WHERE CAPPING IS STRONGEST...AND WILL
CONTINUE TO WATCH THIS AREA WITH THE POSSIBILITY OF STRONG WINDS
WITH THIS LINE...THOUGH SEVERE REPORTS HAVE BEEN FAR AND FEW IN
BETWEEN THROUGH THE NIGHT. CONFIDENCE ON EVOLUTION AND TIMING OF
CONVECTION THROUGH THE DAY IS RATHER LOW...WITH NOT A SINGLE MODEL
HANDLING CURRENT CONVECTION WELL...THOUGH THINK BETTER CHANCES OF
CONVECTION WILL REMAIN NORTH OF INTERSTATE 90 ALONG THE NORTHERN
EDGE OF THE CAP. DOES APPEAR TO BE A GENERAL TREND TO THE EAST
THROUGH THE DAY AS THE UPPER LEVEL WAVE TRACKS EASTWARD...WITH
CONVECTION TAPERING OFF FROM WEST TO EAST INTO THE AFTERNOON. THERE
WILL BE COOLER AIR ADVECTING IN BEHIND THE WAVE...AND THIS WILL BE
REFLECTED IN HIGHS A GOOD 10 DEGREES COOLER THAN YESTERDAY...TOPPING
OUT IN THE MID TO UPPER 70S ACROSS THE AREA.

QUIET WEATHER SHOULD PREVAIL TONIGHT AS UPPER LEVEL AND SURFACE RIDGE
BEGIN TO MOVE INTO WESTERN PARTS OF THE AREA. WITH CLEARING SKIES AND
LIGHT WINDS TONIGHT...WOULD NOT BE SURPRISED TO SEE SOME PATCHY FOG
DEVELOP GIVEN THE WET GROUND OF LATE. HOWEVER...RELATIVELY DRIER AIR
WORKS SOUTHWARD INTO THE AREA BEHIND THE DEPARTING FRONT...SO DO NOT
EXPECT ANYTHING TOO WIDESPREAD OR DENSE AND HAVE NOT MENTIONED IN THE
FORECAST AT THIS TIME. SHOULD BE A FAIRLY COMFORTABLE NIGHT WITH LOWS
IN THE LOWER TO MID 50S.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 508 AM CDT WED JUN 12 2013

RIDGE AXIS SHIFTS SLOWLY EASTWARD THROUGH THE CWA THURSDAY...WITH
RETURN SOUTHEASTERLY FLOW DRAWING WARMER AND MORE HUMID AIR BACK INTO
WESTERN PARTS OF THE FORECAST AREA THURSDAY NIGHT/FRIDAY. INCREASING
THUNDERSTORM CHANCES WILL ACCOMPANY THE WARMTH/HUMIDITY...AS SUBTLE
MID-UPPER LEVEL WAVES SLIDE INTO THE AREA IN SOUTHWEST FLOW ALOFT.
SLIGHT CHANCE OF THUNDERSTORMS IN OUR SOUTHWEST THURSDAY EVENING AS
LOW LEVEL JET BEGINS TO INCREASE INTO CENTRAL SD. HOWEVER BEST CHANCE
THURSDAY NIGHT LOOKS TO HOLD OFF UNTIL AFTER 06Z...AS ELEVATED WARM
FRONT LIFTS NORTHEAST THROUGH THE WESTERN/CENTRAL PORTIONS OF THE
FORECAST AREA. NOT EXPECTING SEVERE STORMS BUT STEEP MID LEVEL LAPSE
RATES LEADING TO STOUT ELEVATED CAPE VALUES...SO SMALL HAIL POSSIBLE
WITH THE MORNING ELEVATED ACTIVITY.

BETTER SEVERE CHANCE MOVES ACROSS THE AREA FRIDAY AFTERNOON/EVENING AS
DEEP LAYER SHEAR INCREASES WITH APPROACHING UPPER TROUGH AND SURFACE
BOUNDARY PUSHING INTO OUR WESTERN CWA. EXPECT LATE NIGHT ELEVATED
ACTIVITY TO PUSH EAST OF THE AREA BY MIDDAY...ALLOWING FOR DECENT
HEATING AHEAD OF THE BOUNDARY IN THE WEST. GFS/NAM BOTH INDICATING
0-6KM BULK SHEAR OF 40-50KTS WITH CONSERVATIVE CAPE VALUES ON THE
ORDER OF 1500-3000J/KG WITH DECREASING CIN JUST AHEAD OF THE BOUNDARY.
SHOULD SEE SCATTERED STORMS DEVELOPING ALONG/WEST OF THE JAMES VALLEY
BY LATE AFTERNOON...WITH STORMS REMAINING ORGANIZED AS THEY MOVE EAST
INTO MN/IA FRIDAY NIGHT. LARGE HAIL/DAMAGING WINDS APPEAR TO BE THE
PRIMARY THREATS FROM POTENTIAL SUPERCELLS FRIDAY AFTERNOON/EVENING...
THOUGH ISOLATED TORNADOES POSSIBLE WITH STORMS THAT DEVELOP ON THE
BOUNDARY. AS THE STORMS SHIFT EASTWARD OVERNIGHT...EXPECT THEM TO
BECOME MORE ELEVATED WITH LARGE HAIL A GREATER THREAT.

CHANCE OF STORMS WILL LINGER INTO THE WEEKEND...WITH FAVORED LOCATION
DEPENDENT ON WHERE RESIDUAL BOUNDARIES END UP. GFS HOLDS THE BOUNDARY
ACROSS THE SOUTHEAST CORNER OF OUR FORECAST AREA SATURDAY AFTERNOON
WHILE OTHER MODELS PUSH IT A LITTLE FARTHER SOUTHEAST. WITH UPPER
LEVEL JET JUST NORTH OF THE AREA AND VERY MOIST LOW LEVEL AIR ALONG
AND SOUTH OF THE BOUNDARY...CONTINUE TO SEE STRONG SHEAR AND HIGH
CAPE VALUES SUPPORTIVE OF ISOLATED SEVERE STORMS. HOWEVER WITH THE
UNCERTAINTY REGARDING BOUNDARY LOCATION...WILL NOT HIGHLIGHT THREAT
IN THE HWO AT THIS TIME.

SUNDAY EVEN MORE MUDDLED WITH LITTLE AGREEMENT AMONG THE LONGER RANGE
MODELS. BROAD CONSENSUS SHOWS UPPER TROUGH AND ASSOCIATED SURFACE LOW
IN NORTHERN MINNESOTA/SOUTHWEST ONTARIO WITH WEAK SURFACE FRONT INTO
WESTERN IOWA/SOUTHEAST NEBRASKA. WILL CARRY ONLY LOW POPS FOR THIS
PERIOD AS MAIN UPPER SUPPORT LOOKS TO BE NORTH OF THE AREA...ALTHOUGH
ECMWF WOULD INDICATE GREATER POTENTIAL AND WILL HAVE TO WATCH.

DRIER SURFACE HIGH THEN SETTLES INTO THE REGION FOR EARLY NEXT WEEK
AND WILL KEEP MONDAY/TUESDAY DRY. TEMPERATURES THROUGH THE LONGER
RANGE LOOK NEAR NORMAL WITH HIGHS IN THE UPPER 70S-LOWER 80S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1039 PM CDT TUE JUN 11 2013

VFR CONDITIONS WITH GUSTY EAST WINDS AND ISOLATED TSTMS THIS LATE
EVENING WILL GIVE WAY TO THUNDERSTORM COMPLEXES MOVING WSW TO ENE
ACROSS THE AREA FROM AROUND MIDNIGHT THROUGH EARLY WEDNESDAY
MORNING. THESE THUNDERSTORMS COMPLEXES ARE EXPECTED TO BE STRONG
TO SEVERE WITH THE MAIN THREAT BEING STRONG/DAMAGING
WINDS...MAINLY ON THE LEADING EDGE OF THE COMPLEXES. LARGE HAIL
WILL ALSO BE A POSSIBILITY. BEHIND THE DEPARTING THUNDERSTORM
COMPLEXES...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.
&&

$$

SHORT TERM...JH/JM
LONG TERM...JH
AVIATION...