381 FXUS63 KDMX 300503 CCA AFDDMX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 1200 AM CDT TUE AUG 30 2011 ...UPDATED 06Z AVIATION DISCUSSION... .SHORT TERM /TONIGHT/... LEE SIDE TROUGH IN FULL SWING OVER THE WESTERN PLAINS WITH SOUTHERN STREAM SYSTEM LOCATED OVER OK THIS AFTERNOON. WARM AIR ADVECTION HAS ALREADY BEGUN AND RETURN MOISTURE FLOW HAS RESULTED IN SOME CONVECTION OVER THE HIGH PLAINS. MODELS CONTINUE IN GOOD AGREEMENT FOR THE OVERNIGHT WITH INCREASING LIFT AND THETAE ADVECTION BY 12Z. WITH CLOUDS ON THE INCREASE AND LIGHT SOUTH WINDS...NOT EXPECTING A RETURN OF FOG TO THE REGION...THOUGH SOME PATCHY FOG MAY DEVELOP NORTHEAST DURING THE EARLY MORNING HOURS. HAVE LEFT AREA DRY UNTIL AFT 06Z WITH INCREASING SATURATION FROM THE WEST. LOWS WILL DROP ONLY INTO THE 50S AND 60S WITH THE CLOUD COVER. SOUNDINGS SUGGEST THAT INSTABILITY WILL BE LIMITED OVERNIGHT UNTIL THE LOW LEVEL JET AND WARM AIR ADVECTION CREATE SOME ELEVATED INSTABILITY FROM 09-12Z TUESDAY. .LONG TERM /TUESDAY THROUGH MONDAY/...A COUPLE OF CONCERNS IN THE EXTENDED WITH THE FIRST ITEM FOR TOMORROWS RAINFALL CHANCES...THEN THE HEAT THURSDAY...AND RAIN CHANCES BY THE END OF THE WEEK. MODELS ARE IN GENERALLY GOOD AGREEMENT THROUGH THURSDAY WITH TIMING OF SHORTWAVE TUESDAY AND WARM UP WEDNESDAY AND THURSDAY. NAM IS THE WARMEST WEDNESDAY AND THURSDAY FOR MAX TEMPS...SO BLENDED WITH THE GFS/NAM/SREF. BY FRIDAY...THE 12Z RUNS OF THE ECMWF AND GFS ARE NOT IN GOOD AGREEMENT WITH TIMING OF COLD FRONT LATER THIS WEEK. LATEST ECMWF HAS TWO SMALLER SHORTWAVES THROUGH FRIDAY AND SATURDAY COMPARED TO THE GFS SHOWING ONE LARGER SYSTEM THROUGH ON FRIDAY. TUESDAY THROUGH THURSDAY...A MID-LEVEL SHORTWAVE AND 500MB VORT MAX WILL BRING SOME RAIN TO THE FORECAST AREA THROUGHOUT MUCH OF THE DAY TUESDAY. THETA-E ADVECTION AND MOISTURE TRANSPORT INTENSIFY BY 12Z TUESDAY ACROSS WESTERN IOWA AND TRANSITION EASTWARD BEFORE MOVING OUT BY 00-03Z WEDNESDAY. BUFR SOUNDINGS CONTINUE TO SHOW A 6 HOUR PERIOD OF DEEP MOISTURE DURING MIDDAY AS WELL AS DECENT ISENTROPIC LIFT ALONG THE 300K TO 310K SURFACES...SO EXPECTING A GOOD STEADY RAIN THROUGH MUCH OF THE DAY TOMORROW BEFORE TAPERING OFF IN THE LATE AFTERNOON/EARLY EVENING. QPF AMOUNTS AND HIGHEST POPS ARE IN THE SOUTH WHERE THE BEST ISENTROPIC LIFT IS LOCATED. WARMER TEMPERATURES IN STORE BY WEDNESDAY AND THURSDAY...WITH THE HOTTEST DAY LOOKING TO OCCUR ON THURSDAY. LARGE UPPER LEVEL RIDGE BUILDS INTO THE CENTRAL PORTION OF THE COUNTRY ON WEDNESDAY AND SHIFTS EAST INTO THE OHIO/TENNESSEE VALLEYS BY THURSDAY. THIS WILL SET UP THE STATE FOR VERY HOT CONDITIONS ON THURSDAY. GOOD MIXING DEVELOPS THROUGHOUT THE DAY THURSDAY...GENERALLY MIXES DOWN FROM ABOUT 900MB OR EVEN NEAR 875MB. NAM SOUNDINGS ARE THE WARMEST ACROSS CENTRAL IOWA...WITH TEMPS NEAR 100 DEGREES OVER THE SOUTH. 850MB TEMPS WARM INTO THE +26C TO 27C RANGE BY 21Z THURSDAY. SURFACE DEW POINTS RANGE IN THE LOWER 70S AND MAY PUSH THE HEAT INDEX INTO THE LOW 100S IN SOME AREAS. SO A CONSIDERATION FOR A HEAT HEADLINE FOR FUTURE FORECAST PACKAGES. FRIDAY INTO SATURDAY...AS MENTIONED ABOVE...THE ECMWF BRINGS ACROSS A SECONDARY COLD FRONT ON SATURDAY WITH ANOTHER SHORTWAVE THAT MOVES OVER THE DAKOTAS/NORTHERN MINNESOTA ON SATURDAY. THE FIRST COLD FRONT THE ECMWF PREDICTS WILL QUICKLY MOVE THROUGH FRIDAY MORNING...WHILE THE GFS IS SLOWER AND NOT UNTIL FRIDAY EVENING. WENT DRY FOR SATURDAY AS THIS WAS FIRST HINT OF A SECONDARY COLD FRONT FROM THE ECMWF...BUT MAY NEED TO ADD SOME POPS ON SATURDAY AFTERNOON IF THIS TREND CONTINUES. SUNDAY AND MONDAY...COLDEST AIR MASS OF THE SEASON WILL AFFECT MUCH OF THE HOLIDAY WEEKEND. LOW TEMPS SUNDAY NIGHT AND MONDAY NIGHT LOOK TO DROP WELL INTO THE 40S ACROSS NORTHERN IOWA WITH SURFACE HIGH PRESSURE DIRECTLY OVERHEAD. LOWERED TEMPS DURING THIS PERIOD. && .AVIATION...30/06Z CEILINGS SHOULD GRADUALLY LOWER DURING THE COURSE THE OVERNIGHT HOURS AS AN UPPER LEVEL SHORTWAVE NEARS THE AREA....BUT SHOULD REMAIN VFR THROUGH THE BEGINNING OF TODAYS RAIN EVENT. THE UPPER MIDWEST RADAR MOSAIC SHOWS WIDESPREAD WEAK TO MODERATE ECHOES ACROSS WESTERN IOWA...BUT SURFACE OBSERVATIONS SEEM TO INDICATE THAT MOST OF THIS IS VIRGA. ONCE THE MAIN SYSTEM ARRIVES...WIDESPREAD RAINFALL AND MVFR TO NEAR IFR CONDITIONS CAN BE EXPECTED FOR MUCH OF THE DAY BEFORE THE SYSTEM PULLS OUT AROUND SUNSET. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...REV LONG TERM...KLP AVIATION...SKOW