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000 FXUS63 KIWX 241739 AFDIWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NORTHERN INDIANA 1239 PM EST TUE NOV 24 2009 .AVIATION.../18Z TAFS/ LOW PRESSURE SYSTEM OVER THE CENTRAL MISSISSIPPI REGION WILL CONTINUE TO PUSH EAST THROUGH THE PERIOD...BRINGING RAIN TO THE REGION. HIGH END MVFR CONDITIONS ARE EXPECTED TO GRADUALLY DETERIORATE TO LOW END MVFR THIS EVENING IN RAIN AND LOW CIGS. PERIODS OF IFR ARE ALSO POSSIBLE WITH INCREASING LL MOISTURE AND LIFT. HAVE CONTINUED THIS TREND IN THE TAFS...OPTING TO HOLD OFF ON IFR MENTION UNTIL A BETTER GRASP ON LOCAL BL CONDITIONS ARE ATTAINED. THERE IS AN OUTSIDE CHANCE FOR A TS AT SBN LATE TONIGHT...BUT WILL LEAVE OUT TS MENTION UNTIL A BETTER HANDLE ON ELEVATED INSTABILITY IS ATTAINED. && .PREV DISCUSSION... /ISSUED 1213 PM EST TUE NOV 24 2009/ UPDATE... QUICK UPDATE TO ADJUST FCST TO REFLECT RECENT OBSERVATIONAL DATA. WEAK SFC BOUNDARY SEEN MAINLY IN DEWPT FIELDS LIFTING THROUGH CWA ATTM WITH AREAS OF DRIZZLE OUT AHEAD OF IT AND ADDED -DZ TO GRIDS AS SUCH. LOWERED HIGHS A TOUCH MAINLY IN THESE AREAS THAT WILL SEE DRIZZLE THROUGH THE EARLY AFTERNOON HRS. OTHERWISE...TIMING OF MAIN BRAND OF PRECIP AHEAD OF OCCLUDED FRONT LOOKS ON TRACK WITH ONLY MINOR TWEAKS NECESSARY TO AFTERNOON POPS/WX. UPDATED GRIDS/ZONES ARE OUT. PREV DISCUSSION... /ISSUED 425 AM EST TUE NOV 24 2009/ SHORT TERM... TODAY THROUGH WEDNESDAY NIGHT... NUMEROUS CHALLENGES IN THE SHORT TERM PERIOD BEGINNING WITH DENSE FOG EARLY THIS MORNING FOLLOWED BY PCPN CHANCES TONIGHT AND THEN PCPN TYPE WED NIGHT. WATER VAPOR SHOWS POTENT SHORT WAVE TROF DIGGING THROUGH CENTRAL PLAINS THIS MORNING WITH SECONDARY KICKER SHORT WAVE MOVING ACROSS THE NORTHWEST CONUS AND CANADIAN BORDER. SURFACE OBSERVATIONS SHOWING WARM AND MOIST AIR LIFTING NORTH AHEAD OF SHORT WAVE ACROSS CENTRAL INDIANA AND ILLINOIS AND MUCH COLDER AIR MOVING INTO THE PLAINS. WEAK HIGH PRESSURE AT THE SURFACE OVER OUR AREA LAST EVENING ALLOWED SURFACE WINDS TO DECOUPLE WHILE SKIES CLEARED. DENSE FOG QUICKLY FORMED AND SPREAD ACROSS MOST OF THE AREA WITH THE EXCEPTION OF FAR NORTHEAST WHERE LOW STRATUS WAS PRESENT. GOES FOG PRODUCT SHOWING ANOTHER AREA OF STRATUS ACROSS CENTRAL IL AND IN SLOWLY LIFTING NORTH IN AREA OF WEAK BUT MOIST ISENTROPIC LIFT. VISIBILITIES HAVE BEEN IMPROVING WHERE THIS STRATUS DECK MOVES OVER AS IDEAL RADIATIONAL COOLING ENDS IN ITS PRESENCE. THUS EXPECT A GRADUAL IMPROVEMENT IN VISIBILITY EARLY THIS MORNING WHERE THIS CLOUD DECK REACHES. MODELS SEEM TO BE A LITTLE SLOW WITH ITS MOVEMENT NORTH BASED ON CURRENT POSITION AND MOVEMENT. GIVEN OBSERVATIONS NOW SHOWING IMPROVING VSBYS ACROSS FAR SOUTHERN COUNTIES...WILL REMOVE ADVISORY FROM THESE AREAS WITH ZONE ISSUANCE BUT KEEP REMAINDER OF ADVISORY INTACT FOR NOW. AFOREMENTIONED STRATUS DECK SHOULD CONTINUE LIFTING NORTHWARD THROUGH THE MORNING. EXPECT CLOUDS TO REMAIN OVER OUR AREA THROUGH THE DAY AND INTO TONIGHT WITH WEAK ISENTROPIC LIFT BEING DEPICTED BY NAM. STRONGER LIFT AND MOISTURE ARRIVE EARLY THIS EVENING IN WEST AHEAD OF FIRST SHORT WAVE AND MOVES ACROSS THE AREA OVERNIGHT. NEARLY ALL SREF AND MREF ENSEMBLE MEMBERS IN GOOD AGREEMENT ON MEASURABLE PCPN ACROSS MOST OF AREA BUT HIGHEST PROBABILITIES NORTHWEST AND NORTH. HAVE INCREASED POPS TO CATEGORICAL THESE AREAS WITH COVERAGE POPS IN 60 TO 70 PERCENT RANGE REMAINDER OF AREA. SEVERAL SHORT WAVES AND REINFORCING SURFACE COLD FRONTS WILL MOVE ACROSS THE AREA WED AND WED NIGHT. SHOULD SEE LULLS IN PCPN BETWEEN EACH WAVE AND TIMING A LITTLE QUESTIONABLE BETWEEN PERIODS. HAVE INCREASED POPS TO LIKELY CATEGORY NORTH WITH FIRST UPPER TROUGH CROSSING THIS REGION ON WED. SECONDARY SHORT WAVE WILL BE DROPPING SOUTH WED NIGHT AND ASCENT AHEAD OF THIS FEATURE MAY GENERATE MORE SHOWERS WED NIGHT. BOUNDARY LAYER INITIALLY WARM FOR ALL RAIN BUT WITH COLD AIR ADVECTION THROUGH THE EVENING EXPECT LOWER LEVELS TO COOL SUFFICIENTLY FOR SNOW TO MIX IF PCPN INDEED OCCURS LATE WED NIGHT. FEW CHANGES WERE MADE TO TEMPERATURES THROUGH THE PERIOD. STILL CONCERNED ABOUT RECOVERY TODAY WITH LOW CLOUDS IN PLACE ALL DAY BUT GOOD WARM SURGE JUST UPSTREAM WITH TEMPERATURES WARMING UNDER THE STRATUS DECK THIS MORNING. CONTINUED TO REMAIN CONSERVATIVE WITH LOWER TO MID 50S WHICH IS NEAR THE LOWER END OF GUIDANCE ENVELOPE AND STILL WELL ABOVE NORMAL FOR LATE NOVEMBER. COOLER AIR FILTERS IN TONIGHT BEHIND FIRST WAVE AND SO BEGINS THE TRANSITION TO MORE SEASONABLE AIR. LONG TERM /THURSDAY THROUGH MONDAY/... STRONG UPPER LOW WILL BE PASSING ACROSS THE FA AT THE START OF THE PERIOD. AS IT DOES...A BRIEF PERIOD OF EITHER DRY CONDITIONS OR POSSIBLE DRIZZLE/FLURRIES WILL OCCUR ESPECIALLY IN THE MORNING. MAIN PUSH OF COLD AIR WILL ARRIVE DURING THE AFTERNOON AND EVENING HOURS. SEVERAL FACTORS LOOK TO COME INTO PLAY TO GIVE A DECENT SHOT AT PRECIP FOR THURS AFTERNOON INTO FRI AM. PLENTY OF MSTR SHOULD BE IN PLACE WITH INCREASING FAVORABLE DELTA T`S...INVERSION HGTS AND TRAJECTORIES TO LEND TO AT LEAST SCT IF NOT POSSIBLY NUMEROUS RAIN AND SNOW SHOWERS WITH POTENTIAL FOR LIGHT SNOW ACCUMS AS SFC TEMPS COOL THURS NGT. FOR NOW HAVE WENT WITH 50 POPS ALL AREAS DURING AFTERNOON/EVE AND LET LATER FORECASTS HONE IN ON FINER DETAILS. INVERSION HGTS AND BEST MSTR WILL SLOWLY BE DIMINISHING ON FRIDAY BUT A FEW SNOW OR RAIN SHOWERS STILL POSSIBLE SO WILL MAINTAIN LOW CHC POPS. HIGH PRESSURE WILL BUILD IN FRIDAY NIGHT INTO SATURDAY NIGHT ALLOWING FOR DRYING CONDITIONS AND HOPEFULLY SOME SUNSHINE TO SALVAGE PART OF THE HOLIDAY WEEKEND. FOCUS WILL THEN TURN TOWARD THE SYSTEM TO TAKE SHAPE ACROSS THE PLAINS IN RESPONSE TO DIGGING HGTS. PRECIP APPEAR TO BE MORE OF A OVERRUNNING SETUP WITH INCREASING SOUTHERLY FLOW. LOW PRESSURE EVENTUALLY DEVELOPS AND TRACKS TOWARDS THE AREA BY MONDAY. THE EXACT TRACK IS STILL VARIABLE WITH MED RANGE MODELS...BUT ENOUGH SIGNALS TO GO AHEAD AND INTRODUCE CHC POPS SUN AFTER INTO MONDAY. THERMAL PROFILES WOULD SUGGEST THAT PRECIP SHOULD FALL IN THE FORM OF RAIN FOR MUCH OF THE EVENT WITH RAIN/SNOW POSSIBLE AT THE END. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ SHORT TERM...LASHLEY LONG TERM...FISHER UPDATE...BJ AVIATION...JC
