Issued by NWS Des Moines, IA
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000 FXUS63 KDMX 300044 AAA AFDDMX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 744 PM CDT SAT AUG 29 2009 .SHORT TERM...TONIGHT UPR TROF ROTATING AROUND LOW OVR NRN GEORGIAN WILL PASS THRU IA TNGT WITH BAND OF CLOUDS ROTATING THRU WI AND ERN MN XPCTD TO DROP SWD ACRS IA. FOR THAT REASON FEEL TEMPS WILL BE LMTD SOMEWHAT IN HOW FAR THEY WILL DROP AND KEPT THE CWA IN THE 40S OVR NGT. WNDS WILL DROP OFF AFT SNST...NOT LKLY TO GO CALM TNGT WITH REFLECTIVE SFC TROF PASSING THRU THE STATE THIS EVE. .LONG TERM...SUNDAY THROUGH SATURDAY UNSEASONABLY COOL AIRMASS OVER UPPER MIDWEST 12Z SUNDAY. SURFACE HIGH PRESSURE FORECAST TO MOVE SOUTHEAST AND BE CENTERED OVER CENTRAL IA 12Z MONDAY. IDEAL RADIATION COOLING SET-UP FOR SUNDAY NIGHT. SKIES SHOULD BE MAINLY CLEAR WITH NEARLY CALM WINDS. LOWERED TEMPS A LITTLE ACROSS CENTRAL IA WITH COLDEST TEMPS IN THE RURAL RIVER VALLEYS. THERE IS A RISK OF SEEING SOME FROST BUT WILL KEEP TEMPS SLIGHTLY ABOVE THE MID 30S AND KEEP FROST OUT FOR NOW. THIS WILL HAVE TO BE REVIEWED IN SUBSEQUENT FORECAST PACKAGES. WILL ADD NEAR RECORD LOW WORDING. GENERALLY USED A MIX OF THE MET/MAV FOR TEMPERATURES WITH MINOR ADJUSTMENTS. GREAT LAKES HIGH PRESSURE EARLY NEXT WEEK WITH RIDGING WEST INTO IA. EXPECT GRADUAL MODERATION OF TEMPS MON/TUE WITH CONTINUED DRY WX. IN THE DAY 4-7 PERIOD...00Z ECMWF...GFS AND GFS ENSEMBLES ALL FORECAST UPPER LOW OVER THE PAC NW TO SLOWLY MOVE EAST INTO THE CENTRAL CONUS BY MIDWEEK. AFTER THAT...THE VARIOUS SOLUTIONS PART WAYS. WITH MAIN BAND OF THE WESTERLIES WELL NORTH...UPPER LOW WILL LIKELY DRIFT SLOWLY ONCE IT REACHES THE CENTRAL CONUS. UPPER LOW TO THE EAST MAY IMPACT WHERE THE CENTRAL CONUS UPPER LOW GOES. THE 00Z ECMWF LIFTS IT OUT TO THE NE WHILE THE GFS SOLUTION DRIFTS IT SOUTH. THE NEW 12Z GFS RUN SLIDES THE UPPER LOW INTO MO BY DAY 7 WHILE THE LATEST ECMWF KEEPS IT TO THE NORTH AND MUCH MORE PCPN OVER IA. INCREASED POPS MIDWEEK SINCE IT SEEMS PROBABLE THAT THERE WILL BE PCPN VCNTY OF THE UPPER AND SFC SYSTEMS. AS THE PAC NW UPPER TROUGH DEVELOPS LATE IN FORECAST PD...EXPECT FLOW TO BECOME INCREASINGLY SOUTHERLY RESULTING IN SLOWLY WARMING TEMPS. PCPN CHANCES BEYOND MIDWEEK ARE UNCERTAIN. GIVEN MODEL UNCERTAINTY...WILL LEAVE FORECAST DRY ON DAY 7. && .AVIATION...30/00Z HIGH PRESSURE BUILDING INTO THE TAF LOCATIONS WILL RELAX THE GRADIENT. MOSTLY CLEAR SKIES AND LIGHT WIND WILL BE THE RULE TONIGHT. THERE IS HOWEVER, ONE CAVEAT. THERE IS A TROUGH PIVOTING AROUND THE GREAT LAKES LOW AND THERE IS SOME LOW CLOUDS ASSOCIATED WITH THIS THAT WILL LIKELY OVERSPREAD NERN IA...POSSIBLY EVEN AFFECTING KDMX. CONDITIONS ARE STILL EXPECTED TO BE VFR EVEN IF CLOUDS DO PUSH IN. SFC FLOW WL BECOME LIGHT LIGHT NERLY AROUND 12Z. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM/AVIATION...FAB LONG TERM...JOHNSON
