381 
FXUS63 KFSD 270209
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
909 PM CDT SAT MAY 26 2012

.DISCUSSION.../ISSUED AT 909 PM CDT/
MAIN UPDATES FOR THE EVENING ARE TO DOWNPLAY THE SEVERE THREAT 
ACROSS THE FORECAST AREA. SCATTERED STORMS THAT HAVE DEVELOPED THIS 
EVENING HAVE STRUGGLED TO MAINTAIN STORM TOPS UP TO 40 KFT AND ANY 
SUBSTANTIAL PRECIPITATION CORE ABOVE ABOUT 25 KFT. ALTHOUGH STORMS 
APPEAR TO HAVE FORMED NEAR OR JUST SOUTH OF ENHANCED SURFACE 
FRONTOGENESIS INDICATED BY RAP ANALYSIS AND SURFACE WINDS...STORMS 
WERE LIKELY ELEVATED WITH A SUBSTANTIAL CAPPING INVERSION STILL 
PRESENT ON THE 00Z KOAX SOUNDING...AND SURFACE TEMPERATURES WELL 
BELOW THE CONVECTIVE TEMPERATURE IN THE MID TO UPPER 90S. IN SPITE 
OF THIS...CANNOT RULE OUT A BRIEF HAILER SPIKING UP IN THE NEXT FEW 
HOURS MAINLY EAST OF INTERSTATE 29...AND COULD STILL SEE MORE ROBUST 
ELEVATED DEVELOPMENT ONCE THE LOW LEVEL JET KICKS IN LATER TONIGHT. 
THE BEST SHEAR PARAMETERS ARE FOCUSED IN THE LOWEST 1-2 KM...SO 
LIKELY WILL NOT BE REALIZED BY ANY STORMS THAT DEVELOP IN THIS 
AREA...SO DO NOT SEE MUCH OF A TORNADO THREAT WITH ANY STORMS THAT 
DEVELOP EITHER LATE THIS EVENING OR OVERNIGHT...AND THINK THAT WINDS 
WILL HAVE A HARD TIME ACCELERATING THROUGH THE INVERSION AS WELL... 
SO THE MAIN THREAT WOULD BE UP TO 2 INCH HAIL AND POSSIBLY A WIND 
GUST UP TO 60 MPH. /LAFLIN

&&

.AVIATION.../FOR THE 00Z TAF ISSUANCE/
STRATUS ALONG AND NORTH OF I-90 WILL CONTINUE TO SEE SOME GRADUAL 
LIFTING THROUGH THIS EVENING. A FEW STORMS OVER NORTH CENTRAL 
NEBRASKA WILL ALSO LIFT NORTHWARD THROUGH AROUND 05Z WITH SEVERE 
WEATHER POSSIBLE MAINLY ACROSS SOUTH CENTRAL SD INTO THE JAMES RIVER 
AREA. SEVERE STORMS WILL POSE THE THREAT OF LARGE HAIL AND DAMAGING 
WINDS AS WELL AS RESTRICTIONS TO VISIBILITY AND CEILINGS. TAF SITES 
APPEAR TO BE ON THE FRINGE OF STORM POTENTIAL...BUT PROBABILITY IS 
TOO LOW FOR THUNDER MENTION AT FSD AND SUX. BETTER THREAT FOR STORMS 
WILL BE SUNDAY LATE AFTERNOON AND EVENING TO THE EAST OF A TYNDALL 
TO DE SMET SOUTH DAKOTA LINE. AGAIN...SEVERE STORMS WILL BE A 
POSSIBILITY...INCLUDING IN FSD AND SUX.

&&

.PREV DISCUSSION.../ISSUED AT 258 PM CDT/
STILL A TOUGH CALL ON TONIGHT WITH EXTREME INSTABILITY ALOFT.  STILL 
A FAIRLY STOUT CAP NEAR 800 MB.  RAP SOUNDINGS WEAKEN THE CAP 
BETWEEN 4-6 PM...BUT THINK THIS IS OVERDONE.  CERTAINLY SOME MASS 
CONVERGENCE ACROSS NORTHEAST NEBRASKA AS THE SURFACE WARMFRONT 
CONTINUES TO LIFT TO THE NORTH...BUT EVEN SATELLITE SHOWS MOSTLY 
CLEAR SKIES ACROSS THE AREA...ANOTHER INDICATION OF THE STRONG CAP.  
HRRR HAS BEEN CONSISTENTLY DEVELOPING CONVECTION THE PAST FEW RUNS 
NEAR THE JAMES RIVER VALLEY...BUT FEEL THIS IS OVERDONE AS ITS 
INITIALIZATION ON SURFACE TEMPERATURES ARE TOO WARM IN THE MODEL BY 
5-10 DEGREES.   INCREASING JET ACROSS NEBRASKA WILL AID IN ASSENT 
SLIGHTLY...BUT STILL THINK IT WILL BE TOUGH TO GET AROUND THE CAP.  
GREATEST POTENTIAL FOR THUNDERSTORM DEVELOPMENT APPEARS TO BE ACROSS 
NORTHERN NEBRASKA...THEN LIFTING NORTHEAST INTO OUR CWA.  IT IS 
CERTAINLY UNSTABLE ALOFT WITH 3500-4000 J/KG OF CAPE.  IF STORMS CAN 
DEVELOP DOWN SOUTH...AND THAT IS A BIG IF...POTENTIAL EXISTS FOR 
LARGE HAIL AND DAMAGING WINDS.  IF STORMS ARE ABLE TO 
DEVELOP...EXPECT THEM TO FOLLOW THE 925 MB FRONT AS IT LIFTS NORTH 
THROUGH THE CWA. LOW TEMPERATURES WILL BE QUITE MILD TONIGHT WITH 
STRONG SOUTHERLY WIND AND LOW LEVEL JET...GENERALLY WARMER THAN IT 
HAS BEEN MUCH OF THE DAY. /BT  

SUNDAY SHOULD PROVE TO BE A VERY WARM AND SOMEWHAT BREEZY DAY 
WITHOUT MUCH THREAT FOR PRECIPITATION UNTIL AFTER ABOUT 300 PM CDT. 
BETTER FORCING WILL BE WELL NORTH OF THE AREA AND THE BETTER CHANCE 
FOR SHOWERS AND THUNDERSTORMS WILL COME WITH THE APPROACH OF A 
FAIRLY POTENT MID AND UPPER LEVEL WAVE. THE MAIN AFFECTS OF THIS 
WAVE WILL BE FELT FROM ABOUT 21Z THROUGH 9Z AND WILL HIT THE POPS 
THE HARDEST DURING THIS TIME. WITH A WEAK WIND SHIFT/DRY LINE MOVING 
INTO THE WESTERN CWA...THE CHANCES FOR CONVECTION WEST OF THE JAMES 
RIVER VALLEY WILL BE MINIMAL WITH THE BEST CHANCE FROM AROUND A 
BROOKINGS TO YANKTON LINE EAST. WILL NOT ISSUE A FLASH FLOOD WATCH 
AT THIS TIME BUT SOME FAIRLY HEAVY RAIN OVERNIGHT IN PARTS OF 
PIPESTONE AND MOODY COUNTIES AS WELL AS EASTERN 
WOODBURY...CHEROKEE...CLAY IOWA AND DICKINSON COUNTIES. BELIEVE THAT 
THE MAIN THREAT WILL BE FOR A FEW LOCATIONS IN MAINLY NORTHWEST IOWA 
AND SOUTHWEST MINNESOTA TO GET AN INCH OR TWO OF RAINFALL WHICH 
COULD SET A FEW CREEKS/STREAMS AND RIVERS OUT OF THEIR BANKS IF IT 
FALLS IN THE RIGHT SPOT. THE OTHER ASPECT OF THIS SYSTEM WILL BE THE 
SEVERE WEATHER THREAT. WITH HE COLD FRONT ALOFT MOVING IN THROUGH 
THE DAY THE CAP WILL WEAKEN QUITE A BIT AND FROM ABOUT 22Z ON WILL 
BE DIFFICULT NOT TO SEE THUNDERSTORM ACTIVITY. AS STORMS DEVELOP THE 
ENVIRONMENT WILL BE SUPPORTIVE OF SEVERE THUNDERSTORMS WITH 1500 TO 
2000 J/KG SFC BASED CAPE AND MODERATE 40 KNOT OR SO BULK SHEAR IN 
THE 0 TO 3KM AND 0 TO 6KM LAYERS. WHILE THE 0 TO 1KM BULK SHEAR IS 
TO POSSIBLY BE UP AROUND 20 KNOTS THE DIRECTIONAL ASPECT IS SEVERELY 
LACKING WITH FAIRLY UNIDIRECTIONAL SHEAR THROUGH THE ATMOSPHERE 
AHEAD OF THE BOUNDARY. SO LIKELY LOOKING AT THE THREAT FOR HALF 
DOLLAR TO GOLF BALL SIZE HAIL AND WIND GUSTS TO 70 MPH. 

BY SUNDAY NIGHT THIS ACTIVITY WILL SWEEP EASTWARD AND BY ABOUT 9Z OR 
10Z LIKELY BE EAST OF THE CWA. COOLER AND MUCH LESS HUMID AIR WILL 
ADVECT IN SUNDAY EVENING LEADING TO LOWS MAINLY IN THE 50S.

MONDAY AND MONDAY NIGHT LOOK COOL AND BREEZY AS WEST TO NORTHWEST 
FLOW KEEPS DRY AND MIXY CONDITIONS IN PLACE. HIGHS WILL MAINLY BE IN 
THE UPPER 60S TO MID 70S WITH LOWS ON MONDAY NIGHT FROM THE MID 40S 
TO NEAR 50. 

TUESDAY WILL CONTINUE COOL DRY WEST TO NORTHWEST FLOW WITH HIGHS IN 
THE 60S AND LOWS IN THE 40S.

IN THE LATTER PERIODS(WED/SAT)...TROUGHING IN THE CENTRAL UNITED 
STATES AND RIDGING IN THE WEST WILL LIKELY LEAD TO A CONTINUED 
THREAT FOR BELOW NORMAL TEMPERATURES THROUGH THE PERIOD...ALTHOUGH 
GRADUAL WARMING IS EXPECTED. WHILE THERE IS STILL A THREAT FOR 
RAINFALL AND ISOLATED THUNDERSTORMS ON WEDNESDAY THE MODELS DO NOT 
AGREE MUCH ON PLACEMENT AND STRENGTH OF JET MAX...SO WILL LEAVE MID 
RANGE POPS IN PLACE. OTHERWISE LOOKING DRY THROUGH THE PERIOD. 
BASICALLY PLANNING ON 60S WEDNESDAY AND THURSDAY AND 70 FRIDAY AND 
SATURDAY. AT THIS TIME IT DOES APPEAR THAT THE RIDGE WILL SPREAD 
ACROSS THE PLAINS BY THE WEEKEND. /08 

&&


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

$$