Issued by NWS Des Moines, IA
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000 FXUS63 KDMX 242338 AAA AFDDMX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE DES MOINES IA 538 PM CST TUE NOV 24 2009 ...UPDATED 00Z AVIATION DISCUSSION... .SHORT TERM /TONIGHT/... A 1007 LOW CURRENTLY OVER SOUTH CENTRAL IOWA IS MOVING TO THE EAST. NAM/GFS IN GOOD AGREEMENT ON MOVEMENT OF THE LOW THROUGH THE STATE TONIGHT. AREAS OF RAIN SHOULD DIMINISH SOMEWHAT IN THE NORTH...WHILE AREAS IN THE VICINITY OF THE LOW WILL HAVE ENOUGH FORCING IN THE LOWER LEVELS TO MAINTAIN THE AREAS OF RAIN. THUNDERSTORMS IN ADVANCE OF A MID-LEVEL DRY SLOT EAST OF THE DES MOINES METRO COULD PRODUCE LOCALLY HEAVY RAINS AND PEA-SIZED HAIL UNTIL AROUND 03Z TONIGHT. POPS ARE DIMINISHING TONIGHT AS THE LOW PULLS AWAY FROM OUR CWA...BUT SOME LINGERING CHANCES WILL REMAIN AS LONG AS WE ARE CAUGHT IN THE WRAP-AROUND FLOW. EXPECT COOLER AND DRIER AIR TO FILTER IN OVERNIGHT FROM THE NORTHWEST AFTER MIDNIGHT. RAIN CHANCES SHOULD DIMINISH EARLY TOMORROW MORNING AS THE MAIN SYNOPTIC FORCING WILL BE WELL EAST THE AREA. .LONG TERM /WEDNESDAY THROUGH TUESDAY/... DEEPENING UPPER LOW WILL DROP SOUTHEAST ON BACKSIDE OF GROWING EASTERN TROF ON WEDNESDAY. WILL SEE QG FORCING AND ISENTROPIC LIFT INCREASE THROUGH THE DAY...PRIMARILY IN THE NORTHEAST AS THE SYSTEM DROPS INTO THE STATE. MAIN CONCERN DURING THIS PERIOD IS WHAT TYPES OF PRECIPITATION WILL WE SEE. SOUNDINGS ARE PRIMARILY ALL BELOW FREEZING EXCEPT FOR THE NEAR SFC TEMPERATURES. DIFFERENT TOOLS AND COBB OUTPUT ALL INDICATE LITTLE IF ANY ACCUMULATING SNOWFALL DURING THE DAY...BUT ALWAYS LEARY WITH A DEEPENING SYSTEM ALONG WITH SFC CAA. AT THIS POINT...HAVE GENERALLY GONE WITH A RAIN/SNOW MIX FOR MOST AREAS WITH LITTLE ACCUMULATIONS. GIVEN THE PAVEMENT TEMPS... WOULDNT EXPECT MUCH TO ACCUMULATE ON PAVED SURFACES ANYWAY. WL SEE PCPN CONTINUE IN THE EASTERN AREAS ON WEDNESDAY EVENING BEFORE STRONGER SUBSIDENCE MOVES ACRS THE AREA ALONG WITH DRIER AIR. WINDS WL BE BRISK FROM THE NORTHWEST DURING THIS ENTIRE TIME AS COLDER AIR POURS INTO THE STATE. THIS SYSTEM WILL PULL AWAY ON THANKSGIVING DAY WITH PARTLY CLOUDY SKIES BUT COOL TEMPERATURES ON THURSDAY. THEREAFTER...UPPER RIDGING WILL PUSH INTO THE CENTRAL US WITH MODERATING TEMPS INTO FRIDAY AND SATURDAY. MEDIUM RANGE MODELS CONTINUE TO BE OUT OF SYNC FOR SYSTEM OVER THE WEEKEND INTO EARLY NEXT WEEK. GFS AND GEM REMAIN MORE PROGRESSIVE WITH THE SYSTEM WHILE THE EURO IS MUCH FARTHER WEST. HAVE GENERALLY STUCK WITH THE PROGRESSIVE NATURE OF THE GFS GIVEN MORE OF A CONCENSUS AMONG MODELS. THIS WOULD MEAN MAINLY DRY CONDITIONS OTHER THAN AN OUTSIDE CHANCE OF PCPN LATE IN THE WEEKEND WITH A FRONTAL PASSAGE. TEMPERATURES WILL BE GENERALLY IN THE NORMAL RANGE DURING THIS TIME. && .AVIATION... 25/00Z...UPPER LEVEL LOW PRESSURE WILL CONTINUE TO WRAP AROUND IFR TO LIFR CIGS ACROSS THE AREA TONIGHT ALONG WITH SOME EMBEDDED SHOWER ACTIVITY THROUGH THIS EVENING. VFR CONDITIONS OVER THE MID MO RIVER VALLEY WILL PROGRESS EAST AFTER MIDNIGHT. THE VFR CONDITIONS WILL BE SHORT LIVED HOWEVER WITH A 3 TO 5 HOUR WINDOW BEFORE THE NEXT SYSTEM RACES OUT OF MONTANA. THIS WILL BRING MVFR TO IFR CONDITIONS BACK FOR WEDNESDAY. POSSIBLE TO HAVE SOME VISIBILITY RESTRICTIONS DUE TO SNOW...ESPECIALLY OVER THE NORTHERN TAF SITES. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...HINSBERGER LONG TERM...COGIL AVIATION...DONAVON