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000 FXUS63 KIWX 251139 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 639 AM EST WED NOV 25 2009 .AVIATION /12Z TAFS/... TOUGH FLYING CONDITIONS FOR THE NEXT 24 HOURS AS ONE LOW PRESSURE SYSTEM LIFTS NORTHEAST INTO MICHIGAN TODAY ONLY TO BE REPLACED BY ANOTHER SYSTEM NOW DROPPING THROUGH THE UPPER MIDWEST WHICH WILL ARRIVE THIS EVENING. SHRAS ASSOCIATED WITH THE FIRST LOW WILL IMPACT BOTH TERMINALS THIS MORNING. EXPECT THESE SHRAS TO BE ACCOMPANIED BY DETERIORATION TO IFR /CIGS/ AS IS OCCURRING ATTM AT SBN. BY AFTERNOON...EXPECT LESS IFR POTENTIAL AS UPPER LOW BEGINS TO PULL AWAY...BUT CAN/T RULE OUT SOME LINGERING IFR CIGS ESP AT SBN THROUGH EARLY AFTERNOON. TONIGHT...AS THE SECOND AREA OF LOW PRESSURE APPROACHES FROM THE WEST...ANOTHER ROUND OF SHOWERS IS POSSIBLE...PARTICULARLY AT SBN. EXPECT GENERALLY MVFR CONDITIONS TO PERSIST FOR THE EVENING AND OVERNIGHT...BUT WILL HAVE TO WATCH FOR POTENTIAL IFR CIGS AT SBN WITH THE SHRAS IN THE EVENING. SOUTHWEST WINDS 12G20KTS ARE EXPECTED TODAY BEFORE DIMINISHING TO AROUND 10KTS FOR THE EVENING AND OVERNIGHT...REMAINING OUT OF THE SOUTHWEST. && .PREV DISCUSSION... /ISSUED 454 AM EST WED NOV 25 2009/ UPDATE... HAVE UPDATED PRODUCTS EARLY THIS MORNING AS RADAR RETURNS HAVE BLOSSOMED NEAR THE CORE OF THE UPPER LOW WITH IR SHOWING COOLING CLOUD TOPS AS THIS FEATURE NEARS THE SOUTHERN SHORE OF LAKE MICHIGAN. CAN/T LET LIKELY POPS RIDE GIVEN THESE TRENDS AND HAVE THEREFORE BUMPED WESTERN AREAS TO CAT...WHILE ALSO EXPANDING THE AREA OF LIKELIES EAST. NO OTHER CHANGES ATTM. PREV DISCUSSION... /ISSUED 349 AM EST WED NOV 25 2009/ SHORT TERM /TODAY THROUGH THURSDAY NIGHT/... A SERIES OF SHORTWAVES WILL IMPACT OUR WEATHER THROUGH THE SHORT TERM PERIOD WITH GRADUALLY DECREASING TEMPERATURES...AND GRADUALLY INCREASING CHANCES FOR SOME SNOWFLAKES TO MAKE AN APPEARANCE. WATER VAPOR AND UPPER AIR ANALYSIS SHOWS FIRST WAVE CENTERED OVER NORTHERN ILLINOIS BEGINNING TO LIFT NORTH AND EAST WITH TIGHTER HEIGHT GRADIENT ON ITS EASTERN FLANK. BAND OF RAINFALL AHEAD OF SURFACE COLD FRONT HAS CLEARED MY EASTERN ZONES AS OF THIS WRITING. WE NOW AWAIT THE ARRIVAL OF THE DEEPER MOISTURE ASSOCIATED WITH THE VERTICALLY STACKED LOW. REGIONAL RADARS SHOWING A PRETTY IMPRESSIVE SPIRAL OF MOISTURE INTO THIS LOW...BUT THE RETURNS ARE RELATIVELY LIGHT. WITH THE TRAJECTORY OF THE LOW...EXPECT THIS SHRA ACTIVITY TO BRUSH MY NORTHWESTERN ZONES...BUT MOSTLY MISS THE SOUTHEASTERN HALF OF THE CWA. LLEVEL MOISTURE WILL REMAIN ENTRENCHED EVEN IN THE SOUTHEASTERN AREAS...HOWEVER...SO ANOTHER DREARY DAY LOOKS TO BE IN STORE WITH PLENTY OF CLOUDS. BY AFTERNOON...THE CENTER OF THE UPPER LOW WILL HAVE PULLED INTO MICHIGAN AND EXPECT A DECREASE IN SHRA ACTIVITY WITH MANY LOCATIONS MAKING IT THROUGH THE AFTERNOON DRY. WITH NO SUN...AND DECENT COLD ADVECTION BEHIND THE DEPARTING LOW/COLD FRONT...DON/T EXPECT TEMPS TO MOVE MUCH AT ALL...AND HAVE INCLUDED THIS STEADY TEMP WORDING IN THE ZONES TODAY. SLIGHTLY UNDERCUT GUIDANCE...FOLLOWING CLOSER TO THE 3 HOURLY MOS TEMPS. NO SOONER WILL THE FIRST WAVE BE OUT OF THE AREA THAN THE NEXT WAVE NOW DIVING SOUTHEAST OVER THE EASTERN DAKOTAS WILL ARRIVE. LIKE THE GFS/S DEEPER AND SLOWER DEPICTION OF THIS FEATURE GIVEN ALL OF THE UPSTREAM JET ENERGY WHICH SHOULD HELP DIG IT FURTHER SOUTH. EVEN WITH THIS SLIGHTLY SLOWER EASTWARD PROGRESSION...EXPECT OUR AREA TO RESIDE ON THE EASTERN FLANK OF THE UPPER LOW WITH DIFFLUENT FLOW ALOFT AND A POTENT AREA OF QVECTOR CONVERGENCE SPREADING OVERHEAD THIS EVENING. BIGGEST QUESTION WILL BE MOISTURE AND THEREFORE HAVE CAUTIOUSLY RAISED POPS TO LIKELY ONLY OVER MY NORTHWESTERN ZONES /AND ONLY THROUGH 6Z/ WHERE MOISTURE LOOKS TO BE THE DEEPEST. AFTER 6Z...EXPECT DEEPEST MOISTURE TO LIFT NORTH FOR A TIME AS A DEFORMATION ZONE DEVELOPS ALONG THE NORTHWESTERN FLANK OF THE NEARING UPPER LOW. SO WILL MAINTAIN NO HIGHER THAN CHC POPS FOR THIS PERIOD. UPPED PREVIOUS LOWS SLIGHTLY...PRETTY CLOSE TO THE MAV VALUES AS COLD ADVECTION OVERNIGHT WILL BE MODEST AND WITH CLOUD COVER AND PRECIP...EXPECT TEMPS TO BE SLOW TO FALL. INTERESTING DAY ON THANKSGIVING AS UPPER LOW SHIFTS EAST AND ALLOWS MORE MEANINGFUL COLD ADVECTION TO DEVELOP. AT THE SAME TIME...BAND OF DEFORMATION PRECIP NORTHWEST OF THE UPPER FEATURE LOOKS TO SAG SOUTH AND EAST. AS THIS DEFORMATION PRECIP ARRIVES...THE FLOW WILL BECOME NORTHWEST AND BEGIN TO PROVIDE LAKE ENHANCEMENT TO ANY ONGOING PRECIP. SO WHILE I EXPECT THE DEFORMATION BAND TO WEAKEN BY AFTERNOON...LAKE ENHANCED PRECIP WILL LIKELY TAKE ITS PLACE. THEREFORE...WILL UP POPS TO LIKELY IN THE WEST...TAPERING TO CHC IN THE EAST. BOUNDARY LAYER TEMPERATURES LOOK MARGINAL FOR A CHANGEOVER TO SNOW DURING THE DAY AND EXPECT THAT THE MOST LIKELY SCENARIO WILL BE FOR SOME WET FLAKES TO MIX IN FROM TIME TO TIME...WITH ANY HEAVIER PRECIP POTENTIALLY BECOMING MORE SNOW. DON/T SEE ANY DAYTIME ACCUMS WITH THIS SCENARIO. TEMPS WILL NOT GO FAR GIVEN THE PRECIP/CLOUDS AND LIKE THE TEMPS WE HAD GOING SO ONLY MADE SOME MINOR TWEAKS HERE...STILL A FEW DEGREES BELOW GUIDANCE. TEMPS ALOFT CONTINUE TO COOL THURSDAY NIGHT AND GIVEN THE TIME OF DAY...THIS MAY BE OUR BEST SHOT AT SOME ACCUMULATING SNOWS. LLEVEL TEMPS STILL WON/T BE ALL THAT COLD...SO WILL NOT GO TO SN EXCLUSIVELY IN THE WEATHER GRIDS. HAVE MAINTAINED LIKELY POPS DOWNWIND OF LAKE MICHIGAN TO ABOUT ELKHART GIVEN MOIST 320 FLOW WITH OTHERWISE CYCLONIC LLEVEL FLOW AND DELTA T/S AROUND 15C WHICH YIELD EQUILIBRIUM LEVELS 7-8KFT. HAVE PAINTED A FEW TENTHS OF AN INCH OF SNOW IN THE GRIDS AT THIS POINT...BUT EXPECT THIS TO BE ON GRASSY SURFACES GIVEN THE MARGINAL BL TEMPS. STILL...IT SHOULD LOOK A LITTLE MORE WINTER-LIKE BY FRIDAY MORNING. TEMPS LOOK TO FALL TO RIGHT AROUND THE FREEZING MARK...EXCEPT PERHAPS A LITTLE HIGHER ALONG THE LAKE MICHIGAN SHORELINE. LONG TERM /FRIDAY THROUGH TUESDAY/... COMBINATION OF 850 RIDGE AXIS SHIFTING ACROSS THE AREA...DECREASING MSTR AND DELTA T`S WILL ALL SPELL THE DEMISE FOR ANY LINGERING RAIN/SNOW SHOWER ACTIVITY DURING THE MORNING. 30 POPS WORK WELL FOR THIS TIME FRAME. DESPITE WAA STARTING IN LOW LEVELS...CLOUD COVER WILL LIKELY LEAD TO ONLY MINIMAL DIURNAL SWING AND RESULTANT HIGHS IN THE UPPER 30S TO AROUND 40. NEXT CHALLENGE WILL BE AMOUNT OF SUNSHINE AND WARMING IN RESPONSE TO NEXT LONG WAVE TROUGH SET TO DEVELOP TO THE WEST INTO THE FIRST PART OF NEXT WEEK. MODELS VARY ON AMOUNT OF WARMING BUT AT LEAST POINT TOWARDS +3 TO +5 C SAT EVENING WITH ECMWF SHOWING +7 TO +9 C. HOWEVER...AMOUNT OF LINGERING LL MSTR WILL BE IN QUESTION WITH RH PROFILES SUGGESTING MUCH OF THE AREA POSSIBLY DEALING WITH MOSTLY CLOUDY SKIES. FOR NOW WILL KEEP CONSERVATIVE ON HIGHS SAT AND SUNDAY AND KEEP WITH PREV GRIDS OF PARTLY TO MOSTLY CLOUDY WITH BEST CHANCE FOR SUN IN SW AREAS. MODELS DO AGREE ON RAPID MOISTENING THROUGH AT LEAST 700 MB BY SUNDAY EVENING AS WEAK LOW PRESSURE TRIES TO DEVELOP IN RESPONSE TO DIGGING UPPER LOW MOVING THROUGH THE CENTRAL PLAINS. CHANCE FOR SHOWERS STILL LOOKS PLAUSIBLE FOR SUNDAY AFTERNOON INTO SUNDAY NIGHT. AFTER THIS MODELS VARY WITH ECMWF AND GEM SHOWING A POSITIVELY TILED AND PROGRESSIVE TROUGH MOVING THROUGH INTO TUESDAY. GFS IS MORE DELAYED WITH DEEP UPPER LOW DEVELOPING ACROSS THE TENNESSEE VALLEY AND BECOMING NEGATIVELY TILTED INTO MID WEEK WITH STG SFC DEVELOPMENT. WITH SLOWER AND STRONGER SYSTEMS BEING THE NORM OF LATE...AM INCLINED TO LEAN TOWARDS THE GFS. HOWEVER...THAT BEING SAID...WILL HOLD OFF ON EXPANDING POPS ANY FURTHER IN THE FORECAST WITH BEST CONFIDENCE IN THE SUNDAY NIGHT/MON TIME FRAME FOR THE TIME BEING. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SHORT TERM...ARNOTT LONG TERM...FISHER AVIATION...ARNOTT
