000 FXUS63 KDVN 232101 AFDDVN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE QUAD CITIES IA IL 301 PM CST MON NOV 23 2009 .SYNOPSIS... 12Z UA ANALYSIS HAS A WEAK TROF MOVING THROUGH THE MID MISSISSIPPI VALLEY. THIS TROF WAS HELPING TO PRODUCE SOME SHRA AND SPRINKLES ACROSS THE IMMEDIATE AREA PER RADAR. A MUCH MORE SUBSTANTIAL SYSTEM WAS OVER THE PLAINS THAT COMPRISED OF TWO PIECES OF ENERGY. THE STRONGER OF THE TWO SYSTEMS WAS OVER WESTERN SOUTH DAKOTA WITH THE SECOND IN WESTERN KANSAS. SATELLITE IMAGERY SHOWED LOW CLOUDS ASSOCIATED WITH LOW LEVEL EASTERLY FLOW OFF LAKE MICHIGAN WERE SLOWLY BREAKING UP AS MID AND HIGH LEVEL CLOUDS STREAM INTO THE AREA. 18Z SFC ANALYSIS HAS A LOW NEAR KDDC WITH A WARM FRONT ACROSS CENTRAL KANSAS. THE COLD FRONT RAN FROM THE LOW INTO NORTHWEST TEXAS AND A DRY LINE EXTENDED FROM THE LOW DOWN INTO THE BIG BEND AREA OF TEXAS. DEW POINTS WERE GENERALLY IN THE LOW TO MID 40S WITH 50S APPROACHING THE KS/OK/MO BORDERS. && .SHORT TERM...TONIGHT AND TUESDAY... THE QUESTION IS HOW LONG WILL THE DRY AIR HOLD. DATA THROUGH 18Z INDICATES THAT NONE OF THE MODELS ARE VERIFYING VERY WELL. IF ONE MODEL HAD TO BE PICKED...THE GEM IS DOING SOMEWHAT BETTER IN TERMS OF VERIFICATION. USING THE GEM WITH SOME INPUTS FROM THE ECMWF...THE FIRST PART OF TONIGHT WILL BE DRY. AFTER MIDNIGHT...A COMBINATION OF TOP DOWN SATURATION AND ADVECTION OF LOW LEVEL MOISTURE WILL SLOWLY SATURATE THE ATMOSPHERE. SOME SPRINKLES OR VERY LIGHT RAIN SHOULD INVADE THE WESTERN QUARTER TO THIRD OF THE CWFA 06Z-09Z BUT WILL NOT MAKE MUCH EASTWARD PROGRESS THROUGH 12Z. WHAT SHOULD HAPPEN IS THAT AS THE ATMOSPHERE IN THAT AREA BECOMES SATURATED...MORE PRECIP SHOULD BREAK OUT AS CONDENSATION PRESSURE DEFICITS LOWER AND FORCING INCREASES. DRY ATMOSPHERE HANGS ON TUESDAY MORNING BUT INCREASED FORCING AND MOISTURE ADVECTION LOWERS CONDENSATION PRESSURE DEFICITS ALLOWING PRECIP TO BREAK OUT. WAA AND HEAVY RAIN TOOLS INDICATE A NICE BAND OF MODERATE RAIN WILL SLOWLY ROTATE NORTHEAST ACROSS THE CWFA DURING THE DAY. AS PWS INCREASE...THE AREAL COVERAGE AND INTENSITY OF THE RAIN WILL INCREASE. CAT POPS LOOK VERY REASONABLE WITH THE HEAVIER RAIN BAND AS IT ROTATES THROUGH THE AREA. CLOUDS AND INCREASING MOISTURE WILL KEEP TEMPERATURES REASONABLY MILD TONIGHT. THE SAME CLOUDS AND PRECIP WILL KEEP TEMPERATURES DOWN ON TUESDAY WITH SOME AREAS STRUGGLING TO REACH 50. THOSE AREAS THAT STAY DRY THE LONGEST SHOULD POP INTO THE LOWER 50S BEFORE THE RAIN BEGINS. ..08.. .LONG TERM...TUESDAY NIGHT THROUGH NEXT MONDAY... TUESDAY NIGHT AND WEDNESDAY...PREFER THE CONSISTENT ECMWF WITH IT/S LATEST SOLUTION OF ROLLING THE NEAR VERTICALLY STACKED LOW COMPLEX RIGHT ACRS THE HEART OF THE DVN CWA TUE NIGHT AND TO THE SOUTHERN LK MI REGION BY WED MORNING. 12Z CANADIAN GEM ALSO SIMILAR TO THE EURO AND WILL GENERALLY USE THE IDEA OFF THESE SOLTIONS AT LEAST THROUGH THE START OF THE WEEKEND. WILL LEAVE THE HIGH POPS FOR RAIN ALONG AND NORTH OF I80 FOR TUE EVENING...BUT ORGANIZED FORCING SHOULD MIGRATE NORTH AND EAST OF THE LOCAL FCST AREA BY 03Z WITH JUST LIGHT RAIN OR EVEN JUST DRIZZLE LEFT IN IT/S WAKE FOR THE REST OF THE OVERNIGHT. WILL TRIM BACK POPS AND INTENSITY SOUTH OF I80. LIFT PROGS EVEN SUGGEST A TEMPORARY BOUT OF SUBSIDENCE FROM MID EVENING UNTIL TOWARD SUNRISE WED MORNING. WILL NOT MENTION IT NOW... BUT WITH LIGHT LLVL CONVERGENT FLOW IN THE VCNTY OF THE LLVL LOW TUE EVENING IN SATURATED BOUNDARY LAYER THERE COULD BE SOME DENSE FOG ISSUES IN AREAS WHERE THE RAIN TAPERS OFF TO DRIZZLE. AS WESTERLY FLOW INCREASES BEHIND EXITING SYSTEM...ANY FOG WILL GET MIXED OUT AFTER 06Z AND INTO WED MORNING. WILL BUMP UP LOW TEMPS A DEGREE OR TWO WITH MANY AREAS NOT DIPPING BELOW THE LOWER 40S. ON WED...CAA STARTS AND SFC TEMPS NOT TO RECOVER MUCH FORM THE MORNING LOWS BY LATE MORNING AND TEMPS WILL EVEN START A STEADY OR SLOW FALL TREND AGAIN WED AFTERNOON. MAY BE A LULL IN MUCH OF THE PRECIP UNTIL LATER IN THE AFTERNOON ESPECIALLY SOUTH OF I80 AND POPS WILL REFLECT THAT THINKING. SECONDARY WAVE OF GULF OF AK ORIGIN STILL ON TRACK TO DUMP DOWN AND TAKE OVER AS THE MAIN FEATURE BY WED EVENING. BANDED PRECIP SHIELD OFF THIS STRONG CLIPPER-LIKE LOW PRESSURE SHOULD PUSH ACRS THE NORTHERN THIRD OF THE DVN CWA AS THE AFTERNOON PROGRESSES. EVEN THOUGH THE LLVL COLD CONVEYOR AND SOME TOP-DOWN COOLING WILL BE INCREASING WED AFTERNOON...NEW THERMAL PROFILES OFF THE 12Z MODEL RUN SOUNDINGS SUGGEST STILL MAINLY ALL RAIN AT THE SFC CWA-WIDE THROUGH AT LEAST 21Z WED AFTERNOON. SOME MIX STILL POSSIBLE OF RAIN...SLEET AND SNOW WEST OF A CID TO DBQ LINE AFTER 21Z. WEDNESDAY NIGHT SNOW EVENT...FORCING OFF NORTHERN FLANK/VORT GRADIENT OF INCOMING WAVE COMBINED WITH ADEQUATE LOW TO MID LEVEL COLUMN SATURATION AND THERMAL PROFILES SUGGEST 1-2 INCHES OF SNOW POSSIBLE WED NIGHT ALONG AND NORTH OF THE HWY 30 CORRIDOR...WITH LIGHTER AMOUNTS DOWN TOWARD THE I80 CORRIDOR. LIKE PREVIOUSLY STATED...ANY ACCUMULATION WILL BE REALIZED MAINLY ON GRASSY AND ELEVATED SFCS. WILL KEEP CHC POPS FOR SNOW SOUTH OF I80 AS WELL WED NIGHT...BUT THE THERMAL PROGS SUGGEST MIXED PRECIP MAY HANG ON IN THESE AREAS ESPECIALLY EAST OF THE MS RVR THROUGH AT LEAST MID WED EVENING. EXPECT WIDESPREAD LOW TEMPS IN THE UPPER 20S TO LOWER 30S EVEN IN THE NORTH WHICH MAY TEMPER ANY SNOW ACCUMULATION POTENTIAL AS WELL AS THE MILD SOIL TEMPS. THANKSGIVING...A LINGERING SNOW SHOWER BAND MAY IMPACT AREAS EAST OF THE MS RVR IN TE MORNING...OTHERWISE TURKEY DAY IS STILL SHAPING UP TO BE A COOL BLUSTERY DAY WITH PASSING SNOW SHOWERS AND FLURRIES. SOME SIGNS OF NORTHWEST FLOW ALOFT ACTUALLY DRAWING IN WARM AIR AS THE COLD CORE SYSTEM PASSES TO THE EAST AND DEEPENS OVER THE GRT LKS. THIS COULD CREATE SOME ICE PELLET SHOWERS THU AFTERNOON THAT MAY BE MIXED WITH SNOW OR EVEN SOME BOUNDARY LAYER RECOVERY FOR A SWITCH BACK TO A COLD RAIN SHOWER. HIGHS LOOK TO RANGE IN THE UPPER 30S TO LOWER 40S. CLEARING AND COLD THU NIGHT ESPECIALLY WEST OF THE MS RVR WITH INCOMING SFC RIDGING. LOWS IN THE 20S. FRIDAY...COLD START TO THE DAY AND SFC RIDGE AXIS/WEAK MIXING SCENARIO SUPPORTS DRY WX BUT TEMPS BELOW GUIDANCE. NEXT WEEKEND/SAT-SUN/...WAA ON SAT WITH A RECOVERY POSSIBLY BACK INTO THE 50S AFTER ANOTHER CHILLY MORNING IN THE 20S. SPLIT FLOW REESTABLISHES ACCORDING TO THE FAVORED 12Z ECMWF WITH SOUTHERN STREAM TRYING TO USHER A SYSTEM AND AT LEAST LIGHT PRECIP THROUGH THE REGION SOMETIME SAT NIGHT OR SUNDAY. MAY JUST GO WITHE SLIGHT CHC POPS FOR SUNDAY FOR NOW WITH MOISTURE RETURN THIS FAR TO THE NORTHWEST STILL AT QUESTION FOR MUCH TO HAPPEN. WILL COOL SUNDAY HIGHS FROM SAT SOME. ..12.. && .AVIATION... VFR CIGS ARE EXPECTED THROUGH 06Z/24. VSBYS ARE MIXED...WITH KCID/KBRL AT 6SM BUT KDBQ/KMLI MAY OR MAY NOT ACHIEVE 6SM PRIOR TO SUNSET. SITES THAT ARE 6SM WL DROP TO 3-5SM PRIOR TO 06Z/24. DRY AIR WL NEED TO BE OVERCOME SO -RA SHOULD HOLD OFF AT ALL SITES UNTIL 12Z/24 OR LATER. TOP DOWN SATURATION SHOULD LOWER CIGS TO 2-3KFT 06Z-12Z WITH 1-2KFT CIGS DVLPG AFT 12Z/24. VSBY OF 2SM AND CIGS OF 1KFT WITH -RA ARE EXPECTED AFT 12Z/24. POTENTIAL FOR 0.5-1KFT IFR CIGS AND VSBYS OF 1SM IN THE HEAVIER RA BANDS 12Z-18Z. ..08.. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$ 08/12