000 FXUS63 KFSD 261556 AFDFSD AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 1055 AM CDT SUN APR 26 2009 .DISCUSSION... LOTS OF ELEVATED POPCORN SHRA/TSRA MOVG ENEWD THRU SERN THIRD OF CWA REST OF MRNG WITH SMALL HAIL AT WORST. PROBABLY REDVLPG THIS AFTN IN SAME AREA...ASSCD WITH CONTINUED DEEPER SLY INFLOW AHEAD OF UPR TROF HANGING BACK TO THE WEST. ELEVATED CONVECTION MOST LIKELY NORTH OF WMFNT...WITH LAPSE RATES ABV 800 MB PSBLY SUPPORTIVE OF RATHER MARGINAL SVR HAIL. QUESTION IS HOW FAR NORTH LWR LVL WMFNT GETS AND IT APPEARS THAT ONLY FAR SE CWA SE OF A LN FM SUX TO SPW HAS PSBLTY OF GETTING CLOSE ...BUT STILL LOOKS A LIT TOO STABLE IN BOUNDARY LAYER FOR MUCH MORE THAN HAILERS...BUT WILL HAVE TO WATCH PROGRESS OF WMFNT. IN THE MEANTIME...KEPT LKLY POPS GOING IN SERN THIRD CWA TDA...BUT EARLIER CUT BACK TO 30 TO 40 CHC SHRA ELSEWHERE IN QUASI DRY SLOT. PREV FCST TEMPS IN THE BALLPARK FOR NOW./RSR && .AVIATION... IFR TO MVFR CIGS IN STRATUS QUO IN MUCH OF CWA TDA AND TNGT. SCT SHRA/TSRA MAINLY SE OF A LN FM MWM TO SUX THRU 00Z...THEN DMNSHG AFT. && .PREV DISCUSSION... WET MORNING ON TAP AS UPPER LEVEL WAVE LIFTS OUT OF NEBRASKA INTO FORECAST AREA. ELEVATED INSTABILITY ALONG AND SOUTH OF A LINE FROM SPRINGFIELD SD TO SLAYTON MN WILL ALLOW FOR SOME EMBEDDED THUNDERSTORMS ACROSS THE SOUTHERN HALF OF THE FORECAST AREA...BUT SINCE INSTABILITY SHOULD REMAIN ON THE LOW SIDE THIS MORNING...AM NOT EXPECTING ANYTHING IN TERMS OF SEVERE WEATHER. SET UP BECOMES MORE INTERESTING THIS AFTERNOON AS WARM FRONT DRAPED ALONG I-80 CORRIDOR AS OF 08Z LIFTS NORTH INTO PORTIONS OF NORTHWEST IOWA THIS AFTERNOON. THOUGH THE NAM AND GFS INITIALIZED IN A FAIRLY SIMILAR FASHION...THE GFS DRAWS SLIGHTLY WARMER AIR INTO THE REGION THAN THE NAM. NAM FORECAST SOUNDING SUGGEST THAT THERE WILL BE A WEALTH OF CLOUDS IN THE WARM SECTOR...WHILE THE GFS SUGGESTS DRY SLOT MAY NOSE NORTHWARD INTO SOUTHEASTERN PORTION OF FORECAST AREA. FOR NOW...HAVE SIDED WITH THE IDEA THAT SKIES WILL BE ABLE TO AT LEAST PARTIALLY CLEAR ACROSS NORTHWEST IOWA. IF THIS IS NOT THE CASE...FORECAST HIGHS WILL NEED TO BE LOWERED FROM KSUX-KSPW AND SOUTHEAST. IF SURFACE IS ABLE TO SUFFICIENTLY HEAT...COULD SEE STORMS AND SEVERE WEATHER DEVELOP ACROSS NORTHWEST IOWA LATE THIS AFTERNOON AS SECOND PIECE OF ENERGY APPROACHES FROM THE SOUTHWEST. WAVE APPEARS TO BE ON A TRAJECTORY CLOSER TO THE COLD FRONT...SO CONVECTION MAY INITIATE MORE ALONG THE COLD FRONT THAN THE WARM FRONT. STILL LOTS OF UPPER LEVEL SUPPORT WITH RIGHT REAR QUADRANT OF UPPER LEVEL JET STREAK INTENSIFYING ACROSS CENTRAL MINNESOTA. SPEED SHEAR AND DIRECTIONAL SHEAR FAIRLY IMPRESSIVE...BUT WITH LIMITED SURFACE HEATING CAPE VALUES ONLY RUNNING AROUND 500 J/KG ACROSS NORTHWEST IOWA. AS COLD FRONT SHIFTS SOUTH AND EAST SUNDAY EVENING SUPPORT FOR PRECIPITATION WANES AS DRIER AIR WORKS INTO THE AREA UNDER NORTHWEST FLOW. HOWEVER...UPPER LEVEL TROUGH REMAINS OVER THE NORTHERN PLAINS ON MONDAY RESULTING IN PARTLY TO MOSTLY CLOUDY SKIES. MODELS PORTEND WAVE SCRAPING THE SOUTHERN EDGE OF FORECAST AREA. LIMITED MOISTURE AND INSTABILITY IS A CONCERN WITH THIS FEATURE...BUT KEPT A LOW END CHANCE OF PRECIPITATION ACROSS NORTHWEST IOWA MONDAY AFTERNOON. TUESDAY LOOKS TO BE DRY AS SURFACE RIDGE ACROSS THE EASTERN DAKOTAS SHIFTS EAST AND SOUTHEASTERLY FLOW DEVELOPS THROUGHOUT THE DAY. FAIRLY STRONG 850 MB WARM AIR ADVECTION/THETA-E ADVECTION MOVES INTO SOUTHWESTERN CORNER OF CWA WEDNESDAY MORNING AND LIFTS NORTHEAST DURING THE DAY. HAVE RAISED POPS SLIGHTLY WITH THIS FEATURE. WITH AN ABUNDANCE OF CLOUDS AND A DECENT POTENTIAL OF PRECIPITATION... LOWERED FORECAST HIGHS ON WEDNESDAY WITH ATMOSPHERE STRUGGLING TO MIX MUCH BEYOND 925 HPA. IN ADDITION...RAISED FORECAST LOWS SLIGHTLY WEDNESDAY NIGHT WITH 925 HPA TEMPS PROGGED AROUND 10 DEGREES C. ACTIVE PATTERN CONTINUES INTO LATTER PORTIONS OF THE WEEK. DID NOT MAKE CHANGES BEYOND WEDNESDAY NIGHT GIVEN ACTIVE WEATHER IN THE NEAR TERM./ BT/MJF && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE MN...NONE. IA...NONE. NE...NONE. && $$