000 
FXUS63 KFSD 012019
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
318 PM CDT WED JUL 1 2009

.DISCUSSION...
HIGH PRESSURE OVER THE JAMES RIVER VALLEY LATE THIS AFTERNOON WILL 
DRIFT EAST INTO SWRN MN/NWRN IA OVERNIGHT. WEAK WARM ADVECTION COULD 
AID IN SPREADING A FEW TSRA INTO AREAS WEST OF THE JAMES RIVER... 
MAINLY AFTER 06Z AND WILL KEEP SOME LOWER CHANCE RANGE POPS OUT 
THERE OVERNIGHT. HOWEVER BETTER INSTABILITY AND LOW LEVEL JET WILL 
REMAIN FOCUSED WEST/SOUTH OF OUR AREA...SO THREAT OF SEVERE WEATHER 
IS MINIMAL AT BEST. WEAK RETURN FLOW WEST OF THE SURFACE RIDGE ALONG 
WITH INCREASE IN MID LEVEL CLOUD COVER SHOULD HELP HOLD TEMPS IN THE 
LOWER TO MID 60S ACROSS THE WEST TONIGHT...WITH MID 50S ACROSS THE 
EAST WHERE MOSTLY CLEAR SKIES AND LIGHT WINDS ARE EXPECTED.   /JH

WITH THE ABSENCE OF DISCERNABLE S/W TO FOLLOW ON THURSDAY OR STRONG 
WAA...JUST OPTED TO FOLLOW THE H85 WIND RIDGE LINE FOR POPS COUPLED 
WITH SOME MID LVL PV. HOWEVER THE MID LVL PV MAY BE AN ARTIFACT OF 
THE MODEL CONVECTION IN THIS CASE. IF THE CONVECTION DOES FOLLOW THE 
H85 RIDGING AND THTE RIDGING...THEN IT WL BE CONFINED GENERALLY 
ALONG AND SOUTH OF A SIOUX CITY IA TO MITCHELL SD LINE IN THE 
MORNING...THEN POSSIBLY INCHING EWD AND NWD IN THE AFTERNOON. BUT 
CERTAINLY ATTM...ONLY SMALL POPS ARE WARRANTED. TEMPERATURE WISE...
GIVEN NAM AND GFS H85 TEMPS...A LOT OF SEASONAL 80S LOOK ON TARGET.

THEN THURSDAY NIGHT THROUGH SATURDAY NIGHT FEATURES ONE OF THOSE 
PESKY...WAVY PATTERNS WITH COOL AIR IN THE MID LVLS. BOTH THE NAM 
AND GFS RH TIME SECTIONS SHOW A LOT OF MOISTURE IN THE MID LEVELS 
MAKING FOR ANYTHING BUT PRISTINE CLOUD COVER. INITIALLY THUR NIGHT 
THROUGH FRI NIGHT...THE HIGHER POPS ARE WARRANTED THROUGH THE SWRN 
HALF OF OUR FA WHERE THOSE AREAS ARE CLOSER TO A POTENTIAL H85 
WRMFNT. THEN SATURDAY IS MARKED BY A STRENGTENING RETURN FLOW LLV 
JET OFF THE SFC BRINGING IN BROAD ISENTROPIC LIFT. THEREFORE KEPT 
OUR CHC POPS GOING CWA WIDE FOR THIS PERIOD. BUT PROBABLY MOST 
INTERESTING AT THIS POINT IS THE SAT NIGHT PERIOD HEADING INTO THE 
EXTENDED. BOTH THE NAM AND GFS POINT AT A WAVE AT H7...WITH THE NAM 
CENTERED IN SERN ND...AND THE GFS IN CENTRAL SD. NOT GETTING TO HUNG 
UP ON THE DETAILS OF PLACEMENT ATTM...BUT IF THIS FEATURE IS REAL...
IT WL MOVE ACROSS THIS FA SAT NIGHT WITH SUBTLE HGT FALLS AND COOL 
AIR ALOFT CONTINUING. WITH AIR THIS COOL IN THE MID LEVELS...IT JUST 
WL NOT TAKE MUCH TO GET ELEVATED CONVECTION GOING SAT NIGHT...OR FOR 
THE OTHER EARLIER PERIODS FOR THAT MATTER. THEREFORE POPS ARE AGAIN 
WARRANTED SAT NIGHT. TEMPERATURES THURSDAY NIGHT THROUGH SAT NIGHT 
JUST LOOK RATHER BENIGN...WITH NO HOT OR COOL AIR. NOT A LOT OF WIND 
EITHER.        /MJF

IN THE EXTENDED SUN THROUGH WED...CONTINUED LOW POPS OVER THE SERN 
HALF OF THE FA WITH THE DEPARTURE OF THE PROJECTED MID LEVEL S/W. 
AGAIN...IF THIS FEATURE IS REAL...WILL HAVE TO RAISE POPS IN THESE 
AREAS IN FUTURE FCSTS. OTHERWISE...THE VARIOUS MEDR MODELS ARE IN 
PRETTY GOOD AGREEMENT IN THE PLACEMENT AND STRENGTH OF AN UPPER 
LEVEL RIDGE ACROSS THE INTERMOUNTAIN WEST ON SUNDAY. BUT THEN DIFFER 
ON THE MOVEMENT EWD OF THIS RIDGE AND STRENGTH. THE ECMWF IS THE 
MOST BULLISH WITH THE HGTS...AND THUS THE SLOWEST IN ITS EWD 
PROGRESSION AS IT SLOWLY MOVES THE RIDGE INTO THE PLAINS BY MID 
WEEK. THE GFS IS NOT SO AMPLIFIED AND QUICKER. WITH THE MID LVL 
TEMPS STILL FAIRLY COOL...EVEN ON THE MORE AMPLIFIED ECMWF...THERE 
WILL PROBABLY BE SOMETHING IN TERMS OF CONVECTION AROUND RIDING THE 
CAP. BUT THE USUAL SPATIAL AND TEMPORAL PLACEMENT OF THIS IS 
PROBLEMATIC. FOR NOW...MAINLY PICKED ON THE TUE NIGHT PERIOD FOR LOW 
POPS AS THE LLV JET LOOKS TO INCREASE IN THAT PERIOD BRINGING UP 
SOME WAA. IF THERE IS A S/W...IT WL NOT TAKE TOO MUCH TO SPARK SOME 
CONVECTION. OTHERWISE CONCERNING TEMPERATURES...THEN LOOK PRETTY 
SEASONABLE.       /MJF

&&

.AVIATION...
VFR CONDITIONS EXPECTED TO DOMINATE THROUGH THURSDAY MORNING...AS 
SURFACE HIGH PRESSURE MOVES EAST ACROSS THE REGION. CHANCE OF -TSRA 
WILL SPREAD INTO AREAS WEST OF THE JAMES RIVER VALLEY TONIGHT...AND 
THROUGH THE MISSOURI RIVER VALLEY ON THURSDAY. BRIEF MVFR VSBYS 
POSSIBLE WITH TSRA...BUT LIKELIHOOD OF TSRA IMPACTING SPECIFIC TAF 
LOCATION LOW SO WILL LEAVE MENTION OUT OF TAFS AT THIS TIME.  /JH

&&

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

&&

$$