000 FXUS63 KIWX 050025 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 724 PM EST THU DEC 4 2008 .AVIATION... 00 UTC TAFS. SHORTWAVE MOVG ACRS SRN GRTLKS THIS EVE WITH CLOUD BEARING WINDS TO VEER/INVERSION HGHTS LIFT AROUND MIDNIGHT BRINGING GRTR CHC FOR MVFR CIGS AND VSBYS TO DIP SOUTH INVOF KSBN. BREVITY OF FAVORED LES CONDS WITH INVERSION HGHTS AGAIN FALLING EARLY AM...TO KEEP PD OF VSBY RESTRICTION LIMITED...THOUGH MVFR CIGS LIKELY INTO EARLY AM IN MOIST CYCLONIC LLVL FLOW. AS WINDS BACK FRI ANTICIPATE LOSS OF HIGH END MVFR CIGS. && .SHORT TERM... CAA/LAKE EFFECT CLOUDINESS CONTS OVER THE GRTLKS REGION...INCLUDING NE 1/2 OF OUR CWA THIS AFTN. SOME LAKE EFFECT SNOW HAS OCCURRED MUCH OF THE DAY ACROSS MUCH OF SRN MI AND ADJACENT NRN INDIANA COUNTIES...HWVR INVERSION WHICH TAMDAR SOUNDINGS INDICATE IS BASED AROUND 3-5KFT...ALONG WITH SHORT WNW FETCH HAS LIMITED INTENSITY OF SNOW SHOWERS IN OUR AREA. COLDER AIR WILL CONTINUE TO ADVECT INTO THE REGION TONIGHT. SHRTWV SEEN ON WATER VAPOR OVER THE UPR MS VALLEY WITH A SFC REFLECTION SEEN IN SFC OBS MOVG INTO NW IL ACCOMPANIED BY A FEW FLURRIES IS EXPECTED TO MOVE EAST ACROSS OUR CWA TONIGHT PSBLY CAUSING SOME FLURRIES OUTSIDE OF LAKE EFFECT AREAS. ALSO INVERSION WILL RISE OVERNIGHT AS THE TROF MOVES THROUGH WHICH SHOULD INCREASE INTENSITY OF LAKE EFFECT SNOW SHOWERS... THOUGH CONTD SHORT FETCH WILL STILL BE LIMITING FACTOR TO SGFNT ACCUMS...WENT WITH 1-2" OVER SRN MI WITH <1" IN ADJACENT IN/OH COUNTIES. H85 TEMPS EXPECTED TO FALL TO AROUND -15C IN OUR CWA OVERNIGHT. UPSTREAM TEMPS THIS MORNING IN THIS AIRMASS IN SINGLE DIGITS/TEENS. WITH LESS SNOW COVER IN OUR AREA THAN IA/NRN IL AND PARTLY TO MOSTLY CLOUDY SKIES EXPECTED OVERNIGHT...KEPT LOWS IN THE TEENS. WITH THERMAL TROF MOVG ACROSS THE AREA ON FRIDAY...TEMPS ONLY EXPECTED TO RISE INTO THE L-M20S. SFC RIDGE WILL MOVE ACROSS THE AREA DURING THE DAY CAUSING WINDS TO BACK TO SW BRINGING LAKE EFFECT TO AN END ACROSS OUR CWA BY EVE WITH THE PSBL EXCEPTION OF NRN BERRIEN COUNTY. AMOUNT OF CLOUDS QUESTIONABLE. BOTH NAM AND GFS INDICATE H925 WILL BE SATURATED...BUT THIS LAYER WAS TOO MOIST IN MODELS TODAY...SO OPTIMISTICALLY WENT WITH PARTLY SUNNY SKIES AGAIN ACROSS SRN PORTION OF THE CWA. ANOTHER STRONG CDFNT WILL DROP SE INTO THE WRN GRTLKS FRI NIGHT. ANY REMAINING LOW CLOUDS EXPECTED TO ADVECT NE OUT OF THE AREA IN THE EVE AS SWLY LOW LEVEL FLOW INCREASES. HIGH CLOUDS WILL BE SPREADING INTO THE AREA AHD OF THE UPR TROF SO EXPECTING MOSTLY CLOUDY SKIES WITH LITTLE TEMP DROP. CONTD WITH SMALL CHC OF SNOW FOR LATE FRI NIGHT AS FRONT APPROACHES...BUT STILL APPEARS BEST CHC OF SNOW WITH THE FRONT WILL BE SATURDAY. && .LONG TERM...(SATURDAY THROUGH THURSDAY)... CONTINUED COLD AND ACTIVE PATTERN THROUGH THE EXTENDED PERIOD WITH QUICK CLIPPER AND LAKE EFFECT SAT NITE/SUN FOLLOWED BY ANOTHER POTENTIAL STRONG SYSTEM MOVING THROUGH THE EASTERN US MIDWEEK. EXTENDED BEGINS WITH CLIPPER SYSTEM IMPACTING NW CWA AS SFC LOW MOVES THROUGH THE UPPER GREAT LAKES. SIGNIFICANT TIMING DIFFERENCES BETWEEN SLOWER NAM/FASTER GFS BRINGING PRECIP INTO THE CWA ON SATURDAY AND HAVE SIDED WITH THE TIMING OF 09Z SREF AS A COMPROMISE. HWVR AS AN ADDNL NOD TO MODEL PERFORMANCE WITH THE PREV SYSTEM HAVE MAINTAINED EARLIER POPS INDICATED BY THE GFS AND UNDERCUT THE MODEL CONSENSUS QPF BY A MARGINAL AMOUNT AS THE 12Z GFS DECREASED QPF FROM 00Z/06Z RUNS POSSIBLY FORESHADOWING SIMILAR OUTCOME OF REALIZING LESSER AMOUNTS. NET RESULT IS LIGHT/MOD SNOW SETTLING IN SATURDAY MORNING AND EXPANDING ACROSS THE CWA WITH RELATIVELY MINOR SYNOPTIC QPF AMOUNTS. ZONE-OMEGA TECHNIQUE INDICATES SNOW RATIOS ON THE ORDER OF 15:1 TRANSLATING TO 2-3 INCH SNOW TOTALS TAPERING OFF FROM NW TOWARDS THE SE. AS SYNOPTIC FORCING WANES IN WAKE OF SFC LOW WINDS TURNING NW PRODUCE LAKE EFFECT SETUP BEGINNING AROUND 00Z SAT AND CONTINUING INTO SUNDAY. BUFR SOUNDINGS SHOW DELTA-T'S PEAKING AT 20 DEG WITH INVERSION LOCATED IN LOW END OF GROWTH ZONE AND UNIDIRECTIONAL 20KT WINDS THROUGH THE LAYER. HAVE REMAINED CONSERVATIVE WITH SNOW AMOUNTS GIVEN LOCATION OF EQL LEVELS HWVR POTENTIAL EXITS FOR MORE SIGNIFICANT SNOW WITH SMALL CHANGE IN THERMAL PROFILE FAVORING BETTER SNOW GROWTH. UPR TROF SHIFTS EASTWARD WITH FLOW RETURNING TO SOUTHERLY BY MONDAY SHUTTING DOWN ANY LEFTOVER LAKE EFFECT MECHANISM AND WARMING TEMPS BACK TO UPPER 20S AND INTO LOW 30S FOR TUESDAY. RELIEF IS POTENTIALLY SHORT LIVED HOWEVER AS MODELS CONTINUE TO SHOW STRONG MID WEEK STORM TAKING SHAPE AS SFC LOW EJECTS NE THROUGH THE EASTERN US WHILE SECOND DEEPER LOW WRAPS UP NEAR BASE OF MID LEVEL TROF ALONG GOMEX WHILE A PUSH OF ARCTIC AIR INTO THE US FOLLOWS. CONSIDERABLE SPREAD AMONG OPERATIONAL MODELS AND ENSEMBLES AS ONE WOULD EXPECT THIS FAR OUT SO HAVE NOT ATTEMPTED TO GO BEYOND THE BIG PICTURE WHICH PAINTS POPS MON-WED AND COLDER TEMPS BEHIND FRONT ON WEDNESDAY. HAVE KEPT LATE WEEK TEMPS ABOVE GUIDANCE AS GFS TENDS TO CONSISTENTLY OVERDO COLD AIR INTRUSIONS SEVERAL DAYS OUT AND ECMWF IS NOT AS AGGRESSIVE WITH ADVANCEMENT OF COLD AIR INTO THE UPPER MISSISSIPPI VALLEY. STAY TUNED. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...SMALL CRAFT ADVISORY UNTIL 7 PM EST SATURDAY FOR LMZ043-046. && $$ SHORT TERM...TAYLOR LONG TERM...LUDINGTON AVIATION...MURPHY