Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 170612 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 112 AM EST WED DEC 17 2014 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... MID LEVEL TROUGH AXIS IS STARTING TO PUSH EAST OF THE FORECAST AREA. STILL SOME PATCHY RAIN WORKING ACROSS THE REGION. EXPECT THIS TO BECOME MORE OF A DRIZZLE WHICH APPEARS TO BE HAPPENING UPSTREAM. COULD EVEN BE SOME FLURRIES MIXED IN. AT THIS POINT EXPECT PRECIPITATION TO END BEFORE TEMPERATURES GET BELOW FREEZING IN THE WESTERN PART OF THE FORECAST AREA. ONLY MADE MINOR ADJUSTMENTS TO TEMPERATURES BASED ON LATEST DATA. CLOUDS AND GUSTY WEST WINDS WILL PERSIST THROUGH THE NIGHT. && .SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/... 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. && .LONG TERM /FRIDAY THROUGH TUESDAY/... 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. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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MVFR LOW CLOUDS WILL PREVAIL THROUGH THE TAF PERIOD. THERE CONTINUE TO BE SIGNIFICANT DISCREPANCIES IN GUIDANCE CONCERNING CLOUDS POTENTIALLY CLEARING AFTER 15Z. BUT BASED ON WHAT HAS BEEN OCCURRING UPSTREAM HAVE OPTED TO KEEP FORECAST PESSIMISTIC AND GO WITH THE NAM AND RAP SOLUTIONS. THERE CONTINUE TO BE SOME POTENTIAL FOR A BRIEF PERIOD OF IFR CEILINGS EARLY IN THE TAF PERIOD WHICH HAVE BEEN HANDLED WITH TEMPO. ALSO THE CYCLONIC FLOW ASSOCIATED WITH THE LOW OVER SE CANADA AND MOVING ENE CONTINUES TO PRODUCE ENOUGH LOW LEVEL CONVERGENCE OVER THE FORECAST THAT VCSH HAVE BEEN INTRODUCED TO ALL TAFS TILL AROUND SUNRISE. THE VCSH WILL BE IN THE FORM OF SNOW SHOWERS AND MAY BRIEFLY LOWER VSBYS INTO THE MVFR RANGE. NO GOOD WAY TO HANDLE THESE VSBYS IN THE FCST DUE TO THE TEMPO IFR CLOUDS SO HAVE OPTED TO LEAVE THEM OUT. SINCE THE INFLUENCE OF THE LOW WILL BE SLOW TO MOVE AWAY FROM THE FORECAST AREA HAVE INTRODUCE WIND GUSTS BACK INTO THE TAFS ALTHOUGH AT LOWER SPEEDS THAN YESTERDAY. WEST WINDS AT 15 WITH GUSTS TO 25 KT WILL DECREASE TO 10 TO 15 WITH GUST 20 KT DURING THE DAY AND W AT 10 KT TONIGHT. OUTLOOK...MVFR CEILINGS WEDNESDAY NIGHT AND THURSDAY. MVFR CEILINGS AND VISIBILITIES POSSIBLE FRIDAY NIGHT INTO SATURDAY NIGHT.
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&& .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...HATZOS NEAR TERM... SHORT TERM...HATZOS LONG TERM...NOVAK AVIATION...HAYDU

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