807 
FXUS63 KFSD 220013
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
713 PM CDT THU AUG 21 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 334 PM CDT THU AUG 21 2014

WEAK FRONT CONTINUES TO SLIDE EAST THROUGH THE CWA THIS AFTERNOON.  
DEW POINTS AHEAD OF THIS BOUNDARY HAVE POOLED INTO THE LOW TO EVEN 
MIDDLE 70S IN SOME LOCATIONS...PUSHING HEAT INDEX VALUES TOWARDS THE 
100 DEGREE MARK.  WE'LL CONTINUE TO MONITOR A LOW END CHANCE FOR AN 
ISOLATED THUNDERSTORM ALONG THIS BOUNDARY AS IT MOVES INTO WESTERN 
MINNESOTA AND NORTHWEST IOWA...BUT OVERALL CONVERGENCE ALONG THIS 
BOUNDARY IS MINIMAL...AND UPPER SUPPORT IS NOT THAT STRONG.  LATEST 
MODIFIED FORECAST SOUNDINGS SHOW SUBSTANTIAL CAPE...BUT STILL SLIGHT 
INHIBITION.  INTO THE EVENING...WILL CONTINUE WITH A SLIGHT CHANCE 
POP ALONG THE BOUNDARY AS IT SETTLES SOUTHEAST WITH HIGHEST POPS IN 
THE EXTREME EASTERN CWA.

SLIGHTLY DRIER AIR HAS FILTERED IN BEHIND THE BOUNDARY THIS 
AFTERNOON...ESPECIALLY IN THE FAR NORTHWESTERN CWA.  HOWEVER...DEW 
POINTS REMAIN NEAR 70 DEGREES AT PEAK HEATING.  WINDS IN THE 
BOUNDARY LAYER TO 925MB WILL TURN LIGHT THIS EVENING AS THE FRONT 
PASSES SOUTHEAST...AND WITH CROSSOVER TEMPS RELATIVELY HIGH...FEEL FOG 
SHOULD BEGIN TO DEVELOP AFTER MIDNIGHT.  

ON FRIDAY WE WILL BEGIN WATCHING UPPER SHORTWAVE TRACK NORTHEAST OF 
OUT THE SOUTHWESTERN UNITED STATES IN THE AFTERNOON. INFLUENCE FROM 
THIS SHORTWAVE WILL HOLD OFF UNTIL THE EVENING HOURS...AS EFFECTIVE 
SURFACE BOUNDARY IS WELL SOUTH OF THE CWA AND FORCING ALOFT IS 
RATHER WEAK.  TEMPERATURES WILL AGAIN CLIMB INTO THE 80S...WITH HEAT 
INDEX VALUES TOPPING OUT NEAR OR SLIGHTLY ABOVE 90 DEGREES.  

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 334 PM CDT THU AUG 21 2014

CONVECTION CHANCES WILL INCREASE ACROSS THE AREA ON FRIDAY NIGHT 
AIDED BY A STRENGTHENING LOW LEVEL JET AND A SHORTWAVE LIFTING UP 
INTO THE REGION. THUNDERSTORM COVERAGE IS EXPECTED TO EXPAND FROM 
THE SOUTHWEST DURING THE OVERNIGHT HOURS...AND HEAVY RAIN WILL BE 
POSSIBLE WITH PRECIPITABLE WATER VALUES RUNNING IN EXCESS OF TWO 
INCHES. THERE DOES APPEAR TO BE ENOUGH INSTABILITY AND SHEAR THAT A 
FEW SEVERE STORMS WILL BE POSSIBLE WITH LARGE HAIL AND DAMAGING 
WINDS. IT WILL AGAIN BE A MILD AND MUGGY NIGHT WITH LOWS IN THE 
UPPER 60S TO NEAR 70.

BEST CONVECTIVE CHANCES WILL RESIDE ACROSS THE NORTHERN HALF OF THE 
CWA ON SATURDAY COINCIDENT WITH THE BETTER FORCING...WITH HEAVY RAIN 
REMAINING A POSSIBILITY. WITH MORE CLOUD COVER...A BIT OF COOLING 
WILL BE REALIZED IN OUR WEST ON THE BACKSIDE OF THE DEPARTING 
WAVE...WITH HIGHS MAINLY AROUND 80. TO THE EAST...TEMPERATURES IN 
THE MID AND UPPER 80S COMBINED WITH DEWPOINTS IN THE LOWER 70S WILL 
YIELD APPARENT TEMPERATURES IN THE LOW TO MID 90S ON SATURDAY 
AFTERNOON. WITH A BOUNDARY LINGERING ACROSS OUR AREA AND CONTINUING 
INFLUENCE FROM A TAIL OF UPPER LEVEL VORTICITY...THUNDERSTORM 
CHANCES WILL PERSIST FOR SATURDAY NIGHT AND SUNDAY. THERMAL PROFILES 
COOL A BIT ON SUNDAY...MORESO IN OUR WESTERN ZONES...SO LOOKING AT 
HIGHS IN THE MID/UPPER 70S THROUGH THE JAMES RIVER VALLEY...TO MID 
80S THROUGH THE SIOUX CITY TO STORM LAKE CORRIDOR.

FOR MONDAY THROUGH THURSDAY...A TROUGH OVER THE WESTERN U.S. SLOWLY 
MIGRATES TO THE EAST THROUGH THE WEEK. MODELS IN AGREEMENT ON 
KEEPING TEMPERATURES BELOW NORMAL THROUGH THE PERIOD...WITH HIGHS 
GENERALLY 70S AND LOWS 50S TO LOWER 60S. THE BETTER CHANCES OF 
CONVECTION THROUGH THE EXTENDED APPEAR TO BE IN THE MONDAY NIGHT TO 
TUESDAY NIGHT TIME FRAME.  

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 712 PM CDT THU AUG 21 2014

WEAK BOUNDARY HAS YET TO PUSH THROUGH KSUX...BUT SHOULD REMAIN INERT
WITH ANY CONVECTIVE ACTIVITY MUCH FURTHER TO THE NORTHEAST ALONG
THE BOUNDARY. NORTHERLY PUSH BEHIND BOUNDARY...BUT WILL OVERALL HAVE
A VERY LIMITED IMPACT ON LOW LEVEL MOISTURE. AREAS OF FOG WOULD
APPEAR FAIRLY LIKELY...BUT FOR THE MOST PART SHOULD REMAIN WITH
MVFR VISIBILITIES WITH MOISTURE LAYER BECOMING MORE SHALLOW...WITH
GREATEST THREAT FOR IFR VISIBILITIES AROUND KSUX. DO NOT EXPECT
CEILINGS WITH FOG DUE TO SHALLOW NATURE.

&&

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

$$

SHORT TERM...DUX
LONG TERM...JM
AVIATION...CHAPMAN