694
FXUS63 KFSD 240933
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
430 AM CDT THU JUL 24 2008
DISCUSSION
BAND OF THUNDERSTORMS PERSISTING THIS MORNING IN STRONG WARM
ADVECTION ZONE AT THE NOSE OF 35-45KT LOW LEVEL JET. HAD SOME PULSY
ELEVATED CORES EARLIER IN THE NIGHT...BUT LARGELY JUST RECEIVING
REPORTS OF VERY HEAVY RAIN AND A LITTLE PEA SIZE HAIL BENEATH THEM.
HAS BEEN SOME REDEVELOPMENT ON THE WESTERN END OF THE TSRA BAND IN
THE LAST HOUR INTO AXIS OF STRONG MOISTURE TRANSPORT ALONG AXIS OF
AROUND 2 INCH PWATS. STRONGEST MOISTURE TRANSPORT SHIFTS INTO MAINLY
NORTHWEST IOWA BY 12Z AS LOW LEVEL JET SHIFTS TO MORE WEST-SOUTHWEST
DIRECTION...AND WOULD EXPECT WESTERN DEVELOPMENT TO WEAKEN AS A
RESULT. WARM ADVECTION/MOISTURE TRANSPORT PUSHES EAST OF OUR CWA BY
15Z...SO WILL TAPER POPS QUICKLY BY MID-LATE MORNING.
SOUTHEAST LOW LEVEL FLOW OUT OF THE TSRA COMPLEX SHOULD KEEP MUCH OF
THE AREA FAIRLY STABLE THROUGH MUCH OF THE DAY...AND HAVE COOLED
HIGHS OFF ACROSS NORTHWEST IOWA WITH MORE CLOUDS AND COOLER LOW
LEVEL AIR LINGERING INTO THE AFTERNOON. WESTERN CWA EXPECTED TO SEE
MORE SUNSHINE AND LATE AFTERNOON INSTABILITY AHEAD OF WEAK COLD
FRONT APPROACHING THE AREA. HAVE KEPT SOME LOWER CHANCE POPS NEAR
THE FRONT IN THE FAR NORTHWEST CWA LATE THIS AFTERNOON...SAGGING
SOUTHEAST WITH THE BOUNDARY TONIGHT. THINK SEVERE THREAT WILL BE
LIMITED TO THIS AREA OF GREATER INSTABILITY ACROSS THE NORTHWEST CWA
DURING THE LATE AFTERNOON/EARLY EVENING...AND EVEN THERE EXPECT
ISOLATED HAIL/WIND THREAT WITH STEEP MID LEVEL LAPSE RATES AND
REALTIVELY DRY MID LEVELS TO WIND SUPPORT...BUT REALLY NOT MUCH
WIND/SHEAR TO SPEAK OF BELOW 600MB TO HELP SUPPORT ANYTHING MORE
THAN MULTICELLULAR PULSE SEVERE.
LOW LEVEL BOUNDARY AND POOLED LOW LEVEL MOISTURE COULD LINGER ACROSS
FAR SOUTHEAST CWA INTO FRIDAY AND WILL KEEP SLIGHT CHANCE OF TSRA IN
THAT AREA. OTHERWISE SOMEWHAT DRIER NORTHERLY FLOW AHEAD OF HIGH
PRESSURE NOSING INTO THE REGION SHOULD LIMIT PRECIP CHANCES THROUGH
THE FIRST HALF OF THE WEEKEND.
GFS AND ECMWF SHOW FRONT TRYING TO LIFT BACK NORTH THROUGH NEBRASKA
SATURDAY NIGHT WITH MOIST RETURN FLOW DEVELOPS INTO THE MISSOURI
VALLEY BY LATE SATURDAY NIGHT AND SUNDAY. GFS SHOWS POTENTIAL FOR
TSRA DEVELOPING OVER THE HIGH PLAINS SATURDAY AFTERNOON TO TRACK
SOUTHEAST INTO THE MISSOURI VALLEY LATER SATURDAY NIGHT...AND WILL
KEEP SOME CHANCE POPS OVER MAINLY THE SOUTHERN PARTS OF THE FORECAST
AREA FOR THE LATTER HALF OF THE WEEKEND.
QUICK MOVING WESTERLY FLOW ALOFT WITH VARIOUS WAVES MOVING ACROSS
THE AREA. DIFFERENCES AMONG THE MODELS IN TIMING OF THE WAVES...WITH
ECWMF CURRENTLY FASTER THAN GFS. EITHER WAY LOOKS UNSETTLED FOR
FIRST PART OF NEXT WEEK AND HAVE NOT MADE CHANGES TO GOING POPS AT
THIS TIME.
AVIATION
GENERAL MVFR TO UPPER END IFR VISIBILITIES AND CEILINGS WILL BE SEEN
AT TAF SITES THROUGH 15Z...WITH ONGOING SHOWER AND THUNDERSTORM
ACTIVITY AROUND KFSD AND KSUX DIMINISHING DURING THE EARLY MORNING
HOURS. VFR CONDITIONS WILL PREVAIL AT ALL SITES AFTER 15Z.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
JH/JM
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