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. && $$