330 FXUS63 KFSD 312104 AFDFSD AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SIOUX FALLS SD 404 PM CDT FRI MAY 31 2013 .SHORT TERM...(THIS EVENING THROUGH SATURDAY) ISSUED AT 404 PM CDT FRI MAY 31 2013 NEARLY STATIONARY UPPER LOW CENTERED OVER CENTRAL PORTIONS OF THE NORTH AND SOUTH DAKOTA BORDER THIS AFTERNOON WILL BEGIN A SLOW WOBBLE EASTWARD AS IT FILLS IN THIS EVENING AND OVERNIGHT. MUCH OF THE FORECAST AREA REMAINS IN THE DRY SOUTHWEST FLOW/DRY SLOTTED AREA OF THIS SYSTEM...HOWEVER AS IT BEGINS AN EASTWARD SHIFT...THE BROAD BAND OF PRECIPITATION CURRENTLY MOVING INTO CENTRAL SOUTH DAKOTA WILL PUSH INTO OUR WESTERN BORDER. RAIN SHOWERS WILL BECOME INCREASINGLY LIKELY ACROSS OUR WESTERN HALF THIS EVENING WITH A FEW EMBEDDED WEAK INSTABILITY THUNDERSTORMS MIXED IN WHILE MORE ISOLATED ACTIVITY IS EXPECTED ELSEWHERE. AFTER MIDNIGHT...RAIN SHOWERS WILL BE LIKELY FOR MUCH OF THE AREA...WITH LESS THAN A QUARTER-INCH OF RAINFALL EXPECTED. GUSTY WINDS WILL PERSIST OVERNIGHT...ONLY SLIGHTLY DIMINISHING. AS THE LOW WOBBLES EAST...WINDS WILL GRADUALLY TRANSITION TO THE WEST THEN NORTHWEST. A DREARY...COOL AND WET START TO JUNE IS EXPECTED ACROSS THE FORECAST AREA SATURDAY WITH THE UPPER LOW MOVING TO OUR EAST AND BREEZY NORTHWEST FLOW SETTLING IN. TEMPERATURES WILL BE AROUND 15 TO 20 DEGREES BELOW NORMAL WITH HIGHS ONLY IN THE MID 50S TO LOWER 60S. LIGHT RAIN SHOWERS WILL GRADUALLY DIMINISH THROUGH THE DAY FROM WEST TO EAST...HOWEVER LOW STRATUS CLOUDS WILL BLANKET THE ENTIRE AREA WELL INTO THE AFTERNOON. NORTHWEST WINDS WILL AVERAGE 15 TO 25 MPH WITH HIGHER GUSTS TO 35 MPH. .LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY) ISSUED AT 404 PM CDT FRI MAY 31 2013 ANY SHOWERS REMAINING AROUND HIGHWAY 71 IN NORTHWEST IA SHOULD END BY SUNSET. AFTER THAT...SUBSIDENCE BEHIND THE RIDGE COMBINED WITH STRONG NORTHERLY FLOW BRINGING DRIER AIR SOUTHWARD WILL ALLOW SKIES TO GRADUALLY CLEAR THROUGH THE NIGHT. IN ADDITION...A SURFACE RIDGE WILL BUILD OVER CENTRAL SD ALLOWING WINDS TO DECREASE ALONG AND WEST OF THE JAMES RIVER WHILE IT REMAINS BREEZY OVER SOUTHWEST MINNESOTA AND NORTHWEST IOWA. THEREFORE COLDEST READINGS WILL BE AROUND HURON AND CHAMBERLAIN IN THE LOWER 40S WHILE UPPER 40S ARE EXPECTED AROUND STORM LAKE. THE RIDGE WILL SLOWLY MOVE ACROSS THE AREA ON SUNDAY. THIS WILL RESULT IN PARTLY TO MOSTLY SUNNY SKIES AND LIGHT WINDS. DESPITE THE LIGHTER WINDS...THE STRONG JUNE SUN SHOULD HELP DEEPEN THE BOUNDARY LAYER SUCH THAT MOST LOCATIONS MIX TO 900 MB. THIS WILL RESULT IN HIGHS FROM THE LOWER 60S ALONG THE BUFFALO RIDGE IN SOUTHWEST MINNESOTA TO NEAR 70 IN SOUTH CENTRAL SD. WITH THE COLD AIR MASS ALOFT AND AMPLE NEAR SURFACE MOISTURE THERE MAY ALSO BE SOME AFTERNOON CUMULUS EAST OF I29. AS THE SURFACE RIDGE MOVES TO THE EAST ON SUNDAY NIGHT...THE FLOW WILL TURN SOUTHEAST. AT THE SAME TIME...700 TO 500 MB LAPSE RATES WILL GRADUALLY DESTABILIZE WITH 7 TO 8 C/KM LAPSE RATES MOVING INTO SOUTH CENTRAL SD BY 12Z MONDAY. AT THE SAME TIME...ALL MODELS SHOW SOME MID LEVEL MOISTURE APPROACHING WITH 700 MB CAPES OF 100 TO 300 J/KG BY MONDAY MORNING. WHILE THERE IS NO REAL UPPER WAVE TO ENHANCE LIFT...THERE MAY BE ENOUGH WARM AIR ADVECTION AROUND 700 MB TO GET A FEW ELEVATED THUNDERSTORMS LATE IN THE NIGHT. WHILE THE BEST CHANCE WILL BE IN WESTERN SD...DID CONTINUE A SLIGHT CHANCE OF THUNDERSTORMS IN SOUTH CENTRAL SOUTH DAKOTA TOWARD DAWN. LOWS ON SUNDAY WILL BE IN THE MID 40S ALONG AND EAST OF I29 WITH LOWER 50S WITH INCREASING CLOUDS AND STRONGER WINDS IN SOUTH CENTRAL SD. ON MONDAY...THE AREA OF WARM ADVECTION AND MIDLEVEL INSTABILITY WILL SPREAD TOWARD I29 THROUGH THE DAY. ALL THREE MODELS CONVECTIVE SCHEMES PRODUCE PRECIPTIATION AND TYPICALLY WITH RELATIVELY COLD AIR ALOFT...MIDLEVEL CONVECTION TENDS TO DEVELOP IN THESE SITUATIONS SO HAVE RAISED POPS TO 30 AND 40 PERCENT OVER MUCH OF SE SD AND NE NEB AS WELL AS ADJACENT AREAS OF SW MN AND NW IA. IT IS LIKELY THERE WILL BE SOME CLEARING BEHIND THIS CONVECTION DURING THE AFTERNOON ALONG AND WEST OF THE JAMES RIVER WHILE THERE SHOULD BE AT LEAST MORNING SUNSHINE EAST OF I29. THE GREATEST UNCERTAINTY WITH TEMPERATURES IS IN THE VICINITY OF I29 WHERE THE BEST CHANCE OF RAIN WILL COME DURING PEAK HEATING. FOR NOW HAVE HIGHS IN THE UPPER 60S TO LOWER 70S BUT SHOULD CLOUDS PERSIST LONGER AND LIMIT SUNSHINE TEMPERATURES COULD BE 2 TO 4 DEGREES COLDER. FARTHER WEST WHERE CLEARING IS MORE LIKELY EXPECT HIGHS IN THE MID 70S. A VERY STRONG UPPER LEVEL WAVE WILL MOVE IN MONDAY NIGHT AND PROGRESS ACROSS THE AREA THROUGH TUESDAY EVENING. THE ECMWF HAS TRENDED TOWARD THE GFS WITH ITS TIMING. THE BEST PV ADVECTION MOVES ACROSS SOUTH DAKOTA WITH MID LEVEL LAPSE RATES BETWEEN 6.5 AND 7.5 C/KM AHEAD OF THE WAVE AND ENOUGH MOISTURE TO RESULT IN LIFTED INDICES AROUND -2 TO -4. WITH LITTLE OR NO CONVECTIVE INHIBITION...CONFIDENCE IS HIGH THAT RAIN AND THUNDERSTORMS WILL DEVELOP MONDAY NIGHT AND SPREAD ACROSS THE ENTIRE AREA ON TUESDAY. ALTHOUGH HEAVY RAIN LIKE THAT OBSERVED ON MEMORIAL DAY WEEKEND IS NOT ANTICIPATED AT THIS TIME...IT APPEARS ANYWHERE FROM A QUARTER INCH TO ONE INCH OF RAIN COULD OCCUR OVER THE PERIOD. WITH THE RAIN THERE WILL BE LITTLE DIURNAL CHANGE WITH LOWS IN THE 50S AND HIGHS GENERALLY IN THE 60S. WITH A RELATIVELY FAST FLOW OVER THE NRN UNITED STATES...MODELS DIFFER ON HOW FAST THIS WAVE WILL MOVE EAST OF THE AREA AND THEN WHEN THE NEXT WAVE WILL APPROACH. THE GFS MOVES THIS FIRST WAVE EAST QUICKLY BUT THEN QUICKLY BRINGS ANOTHER WAVE ACROSS THE MISSOURI VALLEY THURSDAY AND FRIDAY. THE ECMWF HAS TENDED TO BE DRIER WITH THE NEXT WAVE GOING NORTH OF THE AREA LATER IN THE PERIOD. THIS MAKES TIMING OF ANY PRECIPITATION CHANCES LESS CERTAIN ALTHOUGH THE GFS ENSEMBLES SUGGEST THAT THE 12Z GFS IS AN OUTLIER WITH RAIN SOUTH OF I90. FOR THIS REASON...WHILE WE DID NOT THROW OUT THIS SOLUTION COMPLETELY...TENDED TO LOWER POPS FOR WEDNESDAY NIGHT THROUGH THURSDAY NIGHT WITH EITHER DRY WEATHER OR A SLIGHT CHANCE OF PRECIPITATION. ON FRIDAY...THERE APPEARS TO BE AN INCREASE IN MOISTURE AND FORCING FOR ASCENT SO HAVE 20 TO 40 POPS ACROSS THE AREA WITH THE HIGHEST POPS IN THE MISSOURI VALLEY AND NORTHWEST IOWA. AS FOR TEMPERATURES...WITH ZONAL FLOW EXPECTED THERE WILL NOT BE ANY REAL COLD AIR MOVING SOUTH BUT ALSO NOT ANY REAL WARM AIR MOVING NORTH. INSTEAD...EXPECT TEMPERATURES TO SLOWLY MODIFY FROM UPPER 60S TO LOWER 70S ON WEDNESDAY TO LOW TO MID 70S ON FRIDAY. && .AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON) ISSUED AT 113 PM CDT FRI MAY 31 2013 2000 TO 3000 FOOT CEILINGS ACROSS THE FAR NORTHWESTERN FORECAST AREA...INCLUDING THE HURON AND MITCHELL AREAS WILL CONTINUE TO SLOWLY SPREAD SOUTHEAST ACROSS THE FORECAST AREA THROUGH THE OVERNIGHT HOURS TONIGHT...LIKELY REACHING KFSD AROUND 22Z AND KSUX AROUND 08Z. LOW CEILINGS WILL PREVAIL THROUGH THE BULK OF THE DAY ON SATURDAY AS WELL...ALONG WITH POTENTIALLY LOWER CEILINGS IN OCCASIONAL RAIN SHOWERS. GUSTY WINDS WILL PERSIST TODAY INTO SATURDAY WITH ONLY A SLIGHT LULL EXPECTED OVERNIGHT. GUSTS TO 35 KT WILL BE POSSIBLE...ESPECIALLY IN SOUTH CENTRAL SD AND NEAR THE MISSOURI VALLEY. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR SDZ057-058-064-068- 069. WIND ADVISORY UNTIL 1 AM CDT SATURDAY FOR SDZ050-063. MN...NONE. IA...NONE. NE...NONE. && $$ SHORT TERM... LONG TERM...SCHUMACHER AVIATION...