272 FXUS63 KFSD 292019 AFDFSD AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 319 PM CDT THU APR 29 2010 .DISCUSSION... SURFACE ANALYSIS CURRENTLY INDICATING AN AREA OF LOW PRESSURE AND ASSOCIATED COLD FRONT LOCATED JUST TO THE EAST OF THE INTERSTATE 29 CORRIDOR AND CONTINUING TO PUSH EASTWARD A LITTLE FASTER THAN ANTICIPATED. BACK TO THE WEST...ANOTHER SUBTLE WAVE BRINGING A FEW SHOWERS TO THE WESTERN JAMES RIVER VALLEY. SPC MESOANALYSIS SHOWING INCREASING INSTABILITY OUT AHEAD OF THE FRONT...WITH MLCAPE VALUES RANGING BETWEEN 500 AND 1000 J/KG OVER PORTIONS OF WESTERN IOWA AND EASTERN NEBRASKA...THOUGH JUST BARELY GRAZING OUR EXTREME SOUTHEAST. BEGINNING TO THINK THAT CHANCE OF SEVERE STORMS FOR OUR AREA IS DECREASING UNLESS FRONT SLOWS AND CAN INTERACT WITH ANOTHER WAVE WHICH WILL PUSH OUT OF THE WEST CENTRAL PLAINS AFTER 00Z. DO THINK THAT SHOWERS AND THUNDERSTORMS AREA PRETTY GOOD BET IN OUR FAR SOUTHEAST AS THE WAVE TRACKS INTO OUR AREA LATE...BUT BEST LOW LEVEL FORCING/INSTABILITY LOOK TO BE WELL TO OUR EAST BY THAT TIME. LOOKS TO BE LITTLE COOLER TONIGHT BEHIND THE FRONT...WITH LOWS IN THE LOWER 40S WEST TO LOWER 50S SOUTHEAST. /JM THE BROAD TROUGH TO THE WEST WILL SLOWLY WORK EAST ON FRIDAY...WITH A SMALL PIECE OF ENERGY EXPECTED TO LIFT NORTHEAST BY AFTERNOON. WILL KEEP SOME LOW POPS IN THE EAST IN THE MORNING...WITH HIGHER POPS OVER THE EASTERN HALF OF THE CWA DURING THE AFTERNOON AND EARLY EVENING. EXPECT JUST ENOUGH MID LEVEL CONVERGENCE AS WAVE MOVES ACROSS THIS BOUNDARY TO FIRE A FEW SHOWERS AND ISOLATED THUNDERSTORMS. WITH THE COLDER AIR ALOFT...ALBEIT NOT THAT COLD...A FEW HAILERS MAY BE POSSIBLE WITH ANY STRONGER STORMS. ELEVATED SHEAR FROM ABOUT 2-6KM MAY BE ENOUGH TO SUSTAIN AN UPDRAFT IF ONE CAN DEVELOP. REGARDLESS OF ANY HAIL POTENTIAL...FEEL THAT SHOWER CHANCES ARE PRETTY GOOD SO UPPED THE POPS IN THE EAST TO 60-70...FALLING TO 40-50 IN THE EVENING. WITH NOTHING EXPECTED OVERNIGHT. HIGHS TOMORROW BELOW NORMAL AND MAINLY IN THE LOWER 60S WITH WINDS MAINLY LESS THAN 15 MPH. LOWS FRIDAY NIGHT GENERALLY 40 TO 45. SATURDAY AND SUNDAY STILL LOOK MIXY AND WINDY...A LITTLE LESS SO ON SUNDAY...AS A WEST WIND CRANKS UP PRETTY QUICKLY IN THE MORNING AND CONTINUES THROUGH THE DAY. CONTINUE TO AIM A LITTLE BELOW GUIDANCE ON DEW POINTS AS MIXING SUGGESTS LOWER 30S DEW POINTS POSSIBLE IN THE AFTERNOON. OTHERWISE...HIGHS MAINLY IN THE 60S WITH LOWS IN THE UPPER 30S TO LOWER 40S. THE MAIN THING TO WATCH BOTH DAYS WILL BE WHETHER OR NOR THE COLD AIR ALOFT WILL BE ENOUGH TO ALLOW A FEW SHOWERS TO DEVELOP IN THE AFTERNOON AND EVENING...FOR WILL LEAVE DRY AS LOW TO MID LEVEL CONVERGENCE TO REALLY THERE. IN THE LATTER PERIODS(MON/THU)...MODELS COMING TOGETHER A LITTLE BIT MORE ON A SOLUTION FOR THIS TIME FRAME...BUT STILL QUITE A BIT OF DISAGREEMENT. GFS ENSEMBLE SPAGHETTI PLOTS SHOW A HUGE AMOUNT OF VARIANCE STARTING AROUND HOUR 96...0Z MON...AND CONTINUE RIGHT ON THROUGH THURSDAY. THE BIG CHALLENGE WILL BE A DEVELOPING NORTHERN STREAM JET STREAK OVER THE NORTHERN ROCKIES AND HOW THIS WILL PLAY OUT OVER THE WEEK. THE BIGGEST DISCREPANCY LIES AROUND THE PACIFIC NORTHWEST AND HOW MUCH ENERGY WILL DIG IN BEHIND THIS JET STREAK...WHICH WILL DETERMINE WHETHER OR NOT WE GO INTO A FLAT RIDGE FOR THE WEEK...LIKE THE 6Z GFS HINTS AT...OR A BUILDING RIDGE LIKE THE CANADIAN AND ECMWF HINT AT. THE OZ GFS APPEARS TO BE AN OUTLIER AT THIS TIME IN DEVELOPING A VERY STRONG TROF JUST TO THE EAST AND WILL BE DROPPED IN FAVOR OF THE CANADIAN/ECMWF AND TO COME EXTENT THE 6Z AND 12Z GFS. /08 && .AVIATION... EXPECTING PRIMARILY VFR CONDITIONS TONIGHT...THOUGH COULD HAVE TEMPORARY UPPER END MVFR CONDITIONS IN THUNDERSTORMS AROUND KSUX BETWEEN 04Z AND 08Z AS WAVE TRACKS THROUGH THE AREA. /JM && .FSD WATCHES/WARNINGS/ADVISORIES... IA...NONE. MN...NONE. NE...NONE. SD...NONE. $$