National Weather Service Raw Text Product

639 
FXUS63 KFSD 202331
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
631 PM CDT SAT SEP 20 2014

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 256 PM CDT SAT SEP 20 2014

POTENT SHORTWAVE BEGINNING TO MOVE ACROSS NORTH DAKOTA THIS 
AFTERNOON AS A STRONG 140+ KNOT UPPER JET NOSES INTO THE NORTHERN 
PLAINS.  CONVECTION HAS BROKEN OUT AHEAD OF A STRONGER COLD FRONT 
DROPPING SE THROUGH THE REGION. FURTHER SOUTHWEST...A WEAK PRE-
FRONTAL TROUGH CONTINUES TO EDGE EASTWARD TOWARD THE JAMES RIVER 
VALLEY AHEAD OF THE MORE POTENT FRONT...WITH DEW POINTS DROPPING 
INTO THE 40S AND TEMPERATURE QUICKLY MIXING INTO THE LOWER 80S.  
THROUGH THE REMAINDER OF THE AFTERNOON...WILL CONTINUE TO MONITOR FOR 
ADDITIONAL DEVELOPMENT ACROSS MAINLY NORTHERN AND NORTHEASTERN ZONES 
AS THE UPPER WAVE PIVOTS THROUGH THE AREA.  LATEST HI-RES DATA 
CONTINUES TO INDICATE POTENTIAL FOR TAIL END STORMS ON THE SWRN 
FLANK OF MORE ORGANIZED MCS MOVING THROUGH SOUTHWESTERN MN LATE THIS 
AFTERNOON. LOW INSTABILITY AND HIGH SHEAR SETUP WOULD SUPPORT LOW 
TOPPED CONVECTION...AND EVEN A FEW MINI-SUPERCELLS.  THE MAIN RISKS 
WOULD BE DAMAGING WINDS GIVEN AMBIENT FLOW BEHIND THE FRONT AND 
STEEP LOW LVL LAPSE RATES. GIVEN THIN CAPE PROFILES AND PROGRESSIVE 
NATURE OF THE ACTIVITY...WOULD LEAN AGAINST A LARGE HAIL RISK. 

ANY RISK OF CONVECTION WILL BE LIMITED TO THE VERY EARLY EVENING 
HOURS...WITH THE EFFECTIVE FRONT MOVING THROUGH THE AREA BY 7PM. 
ANTICIPATING A BRIEF WINDOW OF RATHER GUSTY WINDS AS THE FRONT MOVES 
THROUGH.

HIGH PRESSURE WILL SETTLE SOUTHWARD THROUGH THE OVERNIGHT HOURS AND 
SUNDAY WILL BE VERY PLEASANT.  WINDS WILL REMAIN FROM THE NORTH WITH 
TEMPERATURES EITHER SIDE OF THE 70 DEGREE MARK.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 256 PM CDT SAT SEP 20 2014

SUNDAY NIGHT STARTS WITH HIGH PRESSURE AND PRETTY CLEAR SKIES OVER 
THE AREA. WITH LIGHT WINDS IT SHOULD PRODUCE LOWS IN THE 40S AND BE 
THE COOLEST NIGHT IN THIS STRETCH. MONDAY AND TUESDAY WILL BRING THE 
SLOW APPROACH FROM THE SW OF CURRENT SOUTHERN CA TROUGH CUTTING 
THROUGH THE ROCKIES RIDGE. THIS SYSTEM IS LIKELY TO BRING HALF 
DECENT MID LEVEL MOISTURE BUT NOT TOO MUCH LIFT AND INSTABILITY. 
TIMING PUTS THE THREAT OF SHOWERS AND POSSIBLE A VERY FEW 
THUNDERSTORMS STARTING MONDAY NIGHT IN SOUTHEAST SD...OVER THE AREA 
FOR TUESDAY THROUGH WEDNESDAY...AND DECREASING THREAT OF 
THUNDERSTORMS WEDNESDAY NIGHT. TEMPERATURES DURING THIS TIME OF 
PLENTY OF CLOUD COVER WILL BE MARKED BY A LOW DIURNAL RANGE WITH 
LOWS IN THE MID TO UPPER 50S AND HIGHS MOSTLY IN THE UPPER 60S TO 
LOW 70S.

THE ABATING OF THE SHOWERS WILL TAKE PLACE WITH THE PASSING OF THE 
WAVE. GFS THEN SHOWS A WAVE BREAKING OFF FROM THE CANADIAN JET AND 
DIGGING AROUND REBUILDING ROCKIES UPPER RIDGE. THE EC SHOWS A BROAD 
BUILDING OF HEIGHTS OVER THE EASTERN TWO THIRDS OF THE USA WITH A 
VERY WEAK INVERTED UPPER TROUGH SLIDING SLOWLY WEST ACROSS THE 
CENTRAL PLAINS SOUTH OF OUR AREA. BECAUSE THIS FEATURE IS SHOWN SO 
WEAK...THIS WOULD TEND TO BRING IN DRY AIR FROM THE RIDGING TO THE 
EAST. WILL THEREFORE GO WITH DRY WEATHER ESPECIALLY SINCE EVEN THE 
GFS SHOWS WEAK THERMODYNAMICS...INCLUDING WEAK INSTABILITY...WITH 
ITS STRONGER SYSTEM. DAYTIME TEMPERATURES THURSDAY THROUGH SATURDAY 
WOULD WARM BACK FULLY INTO THE 70S WHILE LOWS WOULD STAY IN THE MID 
TO UPPER 50S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 627 PM CDT SAT SEP 20 2014

A WIND SHIFT FROM A WEST TO NORTHWEST DIRECTION WILL BE MOVING
SOUTHWARD ACROSS THE FORECAST AREA THIS EVENING...WITH FREQUENT
GUSTS OF AROUND 30 KNOTS MAINLY ALONG AND NORTH OF THE I 90
CORRIDOR THROUGH SUNSET. AT THAT POINT...THE SURFACE WINDS WILL
DECOUPLE FROM THE STRONGER WINDS ABOVE THE SURFACE. THEREFORE BY
THE TIME THE WIND SHIFT GETS TO KSUX SHORTLY AFTER SUNSET...THE
KSUX TAF SITE MAY ESCAPE THE GUSTY WINDS.

&&

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

$$

SHORT TERM...DUX
LONG TERM...
AVIATION...MJ