Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 162046 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 346 PM EST TUE DEC 16 2014 .SYNOPSIS...
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AS LOW PRESSURE MOVES NORTHEAST THROUGH THE GREAT LAKES...A FEW SHOWERS WILL CONTINUE TO BE POSSIBLE INTO THE OVERNIGHT HOURS. COOLER CONDITIONS ARE EXPECTED THROUGH THE REST OF THE WEEK...WITH GENERALLY DRY CONDITIONS. A CHANCE OF RAIN AND SNOW IS IN THE FORECAST FOR SATURDAY...AS WEAK LOW PRESSURE APPROACHES THE REGION FROM THE SOUTH.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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WITHIN A LUMBERING MID-LEVEL TROUGH...CURRENTLY CENTERED OVER THE GREAT LAKES...TWO DISTINCT VORTICITY MAXIMA ARE GRADUALLY PROGRESSING AHEAD. THE FIRST OF THESE IS MOVING ENE THROUGH THE SOUTHERN GREAT LAKES...WITH ITS INFLUENCE BEING FELT ACROSS THE OHIO VALLEY...AND THROUGHOUT THE NWS ILN FORECAST AREA. THE DIURNAL CYCLE TODAY HAS BEEN STUNTED FROM ITS RATHER WARM STARTING POINT...AS COLD ADVECTION ON WESTERLY FLOW HAS ALREADY BEGUN. THOUGH THERE IS NO DISTINCT DIRECTIONAL WIND SHIFT TO HELP PICK OUT A CHANGE IN AIR MASS...THE REST OF THE DAY WILL SIMPLY FEATURE A CONTINUED GRADUAL CLOCKWISE TURNING IN SURFACE WINDS...ALONG WITH STEADY DROPS IN TEMPERATURES AND DEWPOINTS. A STRONGER PUSH OF COLD ADVECTION JUST OFF THE SURFACE APPEARS LIKELY TO BEGIN AFTER 06Z...WHICH SHOULD HELP LEAD TO STEEPER LAPSE RATES NEAR THE GROUND...AND CONTINUED OCCASIONAL WIND GUSTS TO AROUND 20 KNOTS. THIS WILL ALSO LIKELY KEEP RH VALUES RATHER HIGH AT AROUND 925MB-875MB...AND LOW LEVEL CLOUDS ARE NOT EXPECTED TO BREAK BEFORE MORNING. RADAR HAS FINALLY STARTED TO SHOW A DIMINISHING TREND IN COVERAGE FOR RAIN SHOWERS...AND THIS TREND IS EXPECTED TO CONTINUE. LIFT ASSOCIATED WITH THE MID-LEVEL TROUGH IS ALREADY BEGINNING TO DIMINISH...AS THE AXIS IS CLEARING THE CWA TO THE EAST. HOWEVER...WITH THE THICK LOW-LEVEL MOISTURE IN PLACE...THERE APPEARS TO BE A CHANCE FOR SOME VERY LIGHT RAIN OR DRIZZLE TO CONTINUE INTO THE OVERNIGHT HOURS. HRRR SIMULATED REFLECTIVITY HAS...ON SEVERAL RUNS...REFUSED TO GO COMPLETELY DRY DURING THIS PERIOD. FORTUNATELY...IT APPEARS MOST LIKELY THAT ANY RAIN/DRIZZLE/MIST POTENTIAL WILL BE DIMINISHING BEFORE TEMPERATURES DROP BELOW FREEZING. THE 15Z SREF IS VERY LOW ON PROBABILITIES FOR VISIBILITY REDUCTIONS...WHICH MAKES SENSE GIVEN THE EXPECTED WINDS...BUT ALSO LENDS SUPPORT TOWARD WIDESPREAD MIST OR DRIZZLE BEING UNLIKELY. THE MOST LIKELY SCENARIO WILL BE FOR A FEW PATCHES OF LIGHT RAIN OR DRIZZLE THROUGH THE FIRST HALF OF THE OVERNIGHT...POSSIBLY INTO THE EARLY MORNING IN CENTRAL OHIO.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
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AS LOW PRESSURE MOVES NORTHEAST OF THE OHIO VALLEY...THE PRESSURE GRADIENT WILL GRADUALLY RELAX ON WEDNESDAY...BUT CONTINUED COOL WESTERLY FLOW WILL FORCE TEMPERATURES TO REMAIN BELOW AVERAGE. ALTHOUGH DRY CONDITIONS ARE EXPECTED...THE BIGGEST FORECAST CHALLENGE FOR WEDNESDAY WILL BE WITH SKY CONDITIONS. AS HAS BEEN THE CASE SEVERAL TIMES ALREADY THIS COOL SEASON...THE NAM12 SOLUTION FOR LOW-LEVEL MOISTURE HAS REMAINED MUCH THICKER THAN OTHER MODELS (GFS/GEM/ECMWF). KEEPING THE BOUNDARY LAYER WELL MIXED BELOW 3000 FEET THROUGH THURSDAY MORNING...THE NAM12 MAINTAINS A THICK LAYER OF TRAPPED MOISTURE BELOW AN INVERSION. DESPITE WHAT APPEARS TO BE A CONSENSUS FROM THE OTHER MODELS...THE NAM12 HAS SHOWN SUCCESS IN THESE SCENARIOS THANKS TO ITS RESOLUTION IN THE VERTICAL...AND IT CURRENTLY APPEARS TO BE VERIFYING WELL OVER MISSOURI (WHERE OTHER MODELS ARE ALREADY SUGGESTING CLEARER CONDITIONS THAN OBSERVED). SKY GRIDS HAVE THUS BEEN INCREASED ON WEDNESDAY AND INTO WEDNESDAY NIGHT...ALLOWING FOR SOME BREAKS IN THE EVENING. AT 500MB ON WEDNESDAY NIGHT...A NARROW RIDGE WILL EXTEND FROM THE SOUTHERN STATES NORTHWEST INTO THE MIDDLE MISSISSIPPI VALLEY. AS A WEAK SHORTWAVE MOVES OUT OF THE FOUR CORNERS AREA AND RUNS INTO THE RIDGE...IT WILL WEAKEN FURTHER...EVENTUALLY WASHING OUT OVER THE OHIO VALLEY ON THURSDAY. BEFORE THE SYSTEM DISSIPATES...IT APPEARS THAT SOME WEAK ISENTROPIC LIFT WILL ALLOW FOR AN INCREASE IN CLOUDS ON THURSDAY...MOVING FROM SOUTHWEST TO NORTHEAST ACROSS THE OHIO VALLEY. A SLIGHT CHANCE OF PRECIPITATION (MAINLY SNOW) WAS ALSO INCLUDED...AS MOST LOCATIONS ARE LIKELY TO REMAIN DRY...BUT SOME LIGHT PRECIPITATION MAY MAKE IT DOWN. MOST OF THE CLOUDS AND FORCING SHOULD REMAIN ABOVE 5000 FEET...WITH AN EXTREMELY WEAK SURFACE PRESSURE PATTERN PROVIDING NO SUPPORT. COLD ADVECTION ON THURSDAY WILL BE MUCH WEAKER WITH THE LIGHTER FLOW...BUT WITH A RELATIVELY SMALL DIURNAL TEMPERATURE COMPONENT EXPECTED...TEMPERATURES ON THURSDAY ARE EXPECTED TO REMAIN FAIRLY SIMILAR TO VALUES ON WEDNESDAY.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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HIGH PRESSURE AND DRY CONDITIONS WILL START OUT THE LONG TERM PERIOD. THE NEXT SYSTEM WILL BEGIN TO APPROACH THE AREA LATE FRIDAY NIGHT AND INTO THE DAY ON SATURDAY BEFORE TAPERING OFF SATURDAY NIGHT. PRECIPITATION WILL GENERALLY BE IN THE FORM OF LIGHT SNOW ACROSS THE NW HALF OF THE FA. PRECIPITATION IS EXPECTED TO START OFF AS SNOW ACROSS THE SE HALF OF THE FA HOWEVER SOME RAIN IS EXPECTED TO MIX IN DURING THE DAY BEFORE TRANSITIONING BACK TO LIGHT SNOW. HIGH PRESSURE WILL THEN WORK BACK INTO THE AREA FOR SUNDAY AND MONDAY. THE NEXT SYSTEM WILL BEGIN TO WORK INTO THE AREA FOR TUESDAY. MODELS WERE IN SOMEWHAT DECENT AGREEMENT WITH THIS FEATURE HOWEVER THE 12Z ECMWF SOLUTION IS NOW SLOWER AND MORE ROBUST. DID NOT WANT TO JUMP ON THIS NEW SOLUTION QUITE YET AND WENT WITH MORE OF A MODEL BLEND FOR TUESDAY. A MIX OF RAIN AND SNOW ARE EXPECTED HOWEVER AS COLDER AIR BEGINS TO MOVE INTO THE AREA PRECIPITATION LOOKS TO CHANGE OVER TO ALL SNOW SHOWERS DURING THE TUESDAY NIGHT INTO WEDNESDAY TIME PERIOD.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... SURFACE LOW PRESSURE NEAR WESTERN LAKE ERIE EARLY THIS AFTERNOON WILL LIFT SLOWLY EAST/NORTHEAST TO SE CANADA THROUGH THE TAF PERIOD. ONE MORE PIECE OF UPPER LEVEL ENERGY IS EXPECTED TO ROTATE EAST THROUGH THE TAF SITES THIS AFTERNOON. THIS WILL BRING A ROUND OF VFR/MVFR SHOWERS ALONG WITH MVFR CEILINGS. FOR LATE THIS AFTERNOON INTO THE EARLY MORNING HOURS...CEILINGS ARE EXPECTED TO DROP INTO THE IFR CATEGORY FOR A PERIOD OF TIME AS CONSIDERABLE MOISTURE IN THE LOW LEVELS CONTINUES TO WRAP AROUND DEPARTING LOW PRESSURE. SOME MODELS SUGGEST THAT CEILING MAY LIFT ABOVE 1000 FEET BETWEEN 06Z AND 08Z BUT STILL REMAIN BELOW 2000 FEET. ON WEDNESDAY...ANOTHER UPPER LEVEL DISTURBANCE IS EXPECTED TO ROTATE EAST ACROSS THE GREAT LAKES. SURFACE HIGH PRESSURE TO OUR NORTHWEST WILL BE SLOW TO BUILD IN. SOME MODELS SUGGEST THAT IT MAY TAKE AWHILE FOR LOW LEVEL CLOUDS TO ERODE AND/OR SHIFT OFF TO THE NORTHEAST...SO HAVE LIFTED CEILINGS ABOVE 2000 FEET AT THE 30 HOUR KCVG TAF BY 18Z BUT KEPT CEILINGS BROKEN. OUTLOOK...MVFR CEILINGS MAY LINGER INTO WEDNESDAY EVENING. MVFR CEILINGS AND VISIBILITIES POSSIBLE FRIDAY NIGHT INTO SATURDAY. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...HATZOS NEAR TERM...HATZOS SHORT TERM...HATZOS LONG TERM...NOVAK AVIATION...HICKMAN

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