157 
FXUS63 KFSD 182341
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
641 PM CDT TUE JUN 18 2013

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 330 PM CDT TUE JUN 18 2013

THE RIDGE AXIS OVERHEAD BEGINS TO SHIFT EAST TONIGHT ALLOWING FOR A 
RETURN FLOW OF MOISTURE INTO THE AREA...WITH A PRETTY GOOD SURGE OF 
THETAE ADVECTION NOTED LATER TONIGHT. QUESTION BECOMES DO WE 
SATURATE ENOUGH TO GET SOME ELEVATED CONVECTION. AND HOW DOES A WEAK 
CAP AND DRY AIR ABOVE 700 MB IMPACT OUR CONVECTION CHANCES. BEST 
CALL RIGHT NOW WOULD BE FOR INCREASING CHANCES FROM SOUTHWEST TO 
NORTHEAST AFTER MIDNIGHT. ELEVATED CAPE EXPECTED TO STAY UNDER 1000 
J/KG WITH EFFECTIVE SHEAR ON THE LOW SIDE...THUS ANYTHING TONIGHT 
SHOULD BE SUB SEVERE WITH JUST SMALL HAIL THE MAIN THREAT. LOWS 
SHOULD RUN A FEW DEGREES ABOVE NORMAL IN THE WEAK WAA 
REGIME...MAINLY FROM AROUND 60 TO 65.

PROBABLY WILL CONTINUE TO SEE SOME ELEVATED CONVECTION SCATTERED 
ABOUT THE AREA ON WEDNESDAY MORNING. HOWEVER ITS LOOKING 
INCREASINGLY LIKELY THAT SKIES BECOME PARTLY TO EVEN POSSIBLY MOSTLY 
SUNNY FOR A PERIOD DURING THE AFTERNOON. THUS WENT AHEAD AND RAISED 
HIGHS A COUPLE DEGREES...WITH UPPER 70S TO MID 80S FORECAST. QUITE 
POSSIBLE HIGHS END UP EVEN A FEW DEGREES WARMER THAN THIS...BUT 
GIVEN CLOUD COVER UNCERTAINTY DID NOT WANT TO GO TOO HIGH AT THIS 
POINT. NEXT QUESTION IS DO WE GET ANY MORE CONVECTION THAT FIRES IN 
THE AFTERNOON...PROBABLY CLOSER TO SURFACE BASED. DESPITE A WEAK 
SHORTWAVE SEEN ON 500 MB HEIGHT CHARTS...UPPER LEVEL SUPPORT IS 
PRETTY MUCH NEUTRAL...WITH THE LARGE SCALE RIDGE OVERHEAD. LOW AND 
MID LEVEL ISENTROPIC LIFT SHOULD CONTINUE FOR MUCH OF THE DAY 
THOUGH. NOT MUCH OF A CAP IN PLACE...ALTHOUGH SIGNS OF A WEAK NOSE 
OF WARM AIR AROUND 600 MB...AND QUITE A BIT OF DRY AIR ABOVE 700 
MB...WHICH WOULD GET ENTRAINED IN ANY UPDRAFT AND LIKELY NOT ALLOW 
US TO FULLY REALIZE THE FORECAST 2000+ J/KG OF CAPE. SO ITS A TOUGH 
CALL...BUT MOST HI RES MODELS DO POP SOME STORMS...AND THINKING IS 
WE SHOULD BE ABLE TO GET ISOLATED TO SCATTERED ACTIVITY IN THE 
AFTERNOON AFTER ANY ELEVATED MORNING STORMS WIND DOWN. DEEP SHEAR IS 
PRETTY WEAK...ALTHOUGH MAY HAVE JUST ENOUGH LOW LEVEL SHEAR FOR SOME 
MULTICELL ACTIVITY. MOST STORMS WOULD LIKELY BE SUB SEVERE WITH 
SMALL HAIL...ALTHOUGH AN ISOLATED QUARTER SIZE HAIL PRODUCING STORM 
SEEMS POSSIBLE...ESPECIALLY IF WE DO GET CAPES UP AND OVER 2000 J/KG.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 330 PM CDT TUE JUN 18 2013

WEDNESDAY NIGHT INTO THURSDAY WILL SEE THE TAIL END UP THE UPPER 
LEVEL SUPPORT SWING THROUGH. THUNDERSTORMS WILL CONTINUE TO BE 
POSSIBLE WITH A FEW SEVERE THUNDERSTORMS NOT OUT OF THE QUESTION. 
THURSDAY AFTERNOON LOOKS PARTICULARLY INTERESTING IF SOMETHING CAN 
DEVELOP WITH 2500 J/KG CAPE A DECENT SFC TO 3KM BULK SHEAR. NO 
DISCERNIBLE LOW LEVEL FEATURE TO WORK OFF OF BUT THERE IS A MID 
LEVEL WAVE PASSING THROUGH SO THAT MIGHT BE ENOUGH TO GET THINGS 
GOING IF THE CAP CAN BREAK. OTHERWISE PRETTY WINDY WEDNESDAY NIGHT 
AND THURSDAY SO LOWS 65 TO 70 AND HIGHS MAINLY IN THE MID TO UPPER 
80S.

THURSDAY NIGHT INTO FRIDAY NIGHT CONTINUES THE THREAT FOR SEVERE 
THUNDERSTORMS AND HEAVY RAINFALL...WHICH CHANCES LIKELY BETTER 
DURING THIS TIME FRAME. THE UPPER LEVEL TROUGH TO THE WEST BEGINS TO 
WORK ONTO THE PLAINS WHICH HELPS FOCUS THE LOW LEVEL JET AND 
INCREASES SHEAR ALOFT A BIT AS WELL. WILL JUST BE A MATTER OF 
BREAKING THE CAP DURING THE DAY...WHICH SHOULD OCCUR 
SOMEWHERE...LIKELY INT HE WESTERN CWA OR POINTS WEST OF THERE...THEN 
FORM INTO A LARGER SCALE MCS AT NIGHT. VERY WARM CONDITIONS THROUGH 
THIS TIME WITH LOWS 65 TO 70 AND HIGHS 85 TO 95.

SATURDAY INTO NEXT TUESDAY LOOKS PRETTY BUSY AS WELL BUT WILL NOT 
REALLY TRY TO PIN ANYTHING DOWN AT THIS TIME. THE UPPER LEVEL WAVE 
EJECTS TO THE NORTHEAST OVER THE WEEKEND THEN A FLAT RIDGE WITH 
FAIRLY STRONG WEST WINDS ALOFT CONTINUES TO SUPPORT A FAVORABLE 
ENVIRONMENT FOR SEVERE THUNDERSTORMS...ESPECIALLY WITH A LOW LEVEL 
BOUNDARY FLOATING AROUND. OVERALL LOWS IN THE 60S AND HIGHS IN THE 
80S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 641 PM CDT TUE JUN 18 2013

VFR CONDITIONS EXPECTED TO DOMINATE THROUGH THE PERIOD. HOWEVER
ISOLATED THUNDERSTORMS WILL BE POSSIBLE WEST OF THE JAMES RIVER
VALLEY MAINLY AFTER 06Z TONIGHT...WITH THE POTENTIAL FOR SCATTERED
THUNDERSTORMS THEN EXPANDING EASTWARD ACROSS THE AREA AFTER 12Z
WEDNESDAY MORNING. BRIEF MVFR VISIBILITY WILL BE POSSIBLE IN ANY OF
THESE STORMS...HOWEVER EXPECTED AREAL COVERAGE IS TOO LOW TO INCLUDE
MENTION IN TAFS AT THIS TIME. INCREASING SOUTHEAST-SOUTH LOW LEVEL
FLOW EXPECTED AS SURFACE RIDGE AXIS SHIFTS EAST OF THE FORECAST
AREA LATE TONIGHT/WEDNESDAY MORNING...WITH GUSTS AT OR ABOVE 20KTS
LIKELY FOR MOST AREAS AFTER 17Z.

&&

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

&&

$$

SHORT TERM...CHENARD
LONG TERM...08
AVIATION...JH