Area Forecast Discussion
Issued by NWS Wilmington, OH

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000 FXUS61 KILN 210005 AFDILN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON OH 705 PM EST SAT DEC 20 2014 .SYNOPSIS... WEAK SURFACE HIGH PRESSURE WILL GRADUALLY MOVE EAST OF THE OHIO VALLEY BY SUNDAY. AS SOUTHERLY WIND FLOW INCREASES...TEMPERATURES WILL BEGIN TO WARM EARLY IN THE WEEK. CHANCES FOR RAIN WILL INCREASE BY TUESDAY...AS A STRONG LOW PRESSURE SYSTEM MOVES INTO THE GREAT LAKES. WINDY AND COOL CONDITIONS ARE EXPECTED AFTER THE LOW MOVES AWAY IN THE MIDDLE OF THE WEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... THE THICK AND EXTREMELY PERSISTENT CLOUDS AT AROUND 2000 FEET WILL HAVE ONE MORE FORECAST PERIOD TO HANG AROUND. THE 12Z KILN SOUNDING WAS VERY SIMILAR TO PREVIOUS OBSERVATIONS...WITH MOISTURE TRAPPED UNDER A SHARP INVERSION AT AROUND 875MB. THE ONE DIFFERENCE WITH THE SOUNDING THIS MORNING WAS A GREATER PRESENCE OF MID AND HIGH LEVEL MOISTURE...A PRODUCT OF THE SHORTWAVE ALREADY MOVING OUT OF THE OHIO VALLEY. BEHIND THIS WAVE...THE HIGHER CLOUDS ARE CLEARING...AND VISIBLE SATELLITE IS PROVIDING AN ENLIGHTENING PICTURE OF THE PROGRESSION OF THE LOW-LEVEL CLOUD SHIELD. WHAT HAS BECOME EVIDENT TODAY IS THAT EROSION OF THESE CLOUDS (GENERALLY SOUTH AND WEST OF THE ILN FORECAST AREA) HAS BECOME A LITTLE MORE PRONOUNCED. WITH THE LOWER OHIO VALLEY NOW ON THE BACK SIDE OF AN 850MB RIDGE...SOME SLIGHT WARM ADVECTION HAS BEGUN...AND THIS WILL START TO AFFECT THE MIDDLE OHIO VALLEY BY EARLY SUNDAY MORNING. UNTIL THEN...THE PERSISTENCE FORECAST WILL LARGELY PAY OFF. WITH A FEW BREAKS IN THE CLOUDS EXPECTED...AND NEARLY CALM WINDS...MIN TEMPS MAY DROP A COUPLE DEGREES BELOW OBSERVED NUMBERS FROM EARLY SATURDAY MORNING. WITH RADAR STILL SHOWING A FEW LIGHT ECHOES IN NORTHERN AND CENTRAL OHIO...FLURRIES WERE KEPT IN THE FORECAST IN THE COLUMBUS AREA FOR A FEW HOURS LATE THIS AFTERNOON. CURRENT OBSERVATIONS ARE COMING IN WITHOUT MENTION OF PRECIPITATION...SO IT SEEMS LIKELY THAT MOST OF THE OBSERVED RETURNS ARE NOT REACHING THE GROUND. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... A PATTERN CHANGE WILL BEGIN ON SUNDAY ACROSS THE OHIO VALLEY. SURFACE HIGH PRESSURE WILL BE CENTERED WELL EAST OF THE REGION...AND THE AXIS OF A LOW-AMPLITUDE MID-LEVEL RIDGE WILL BE SHIFTING GRADUALLY TO THE EAST AS WELL. THIS WILL SET UP A REGIME OF DEEP SOUTHERLY FLOW BY SUNDAY NIGHT...ESPECIALLY ONCE THE GRADIENTS BEGIN TO TIGHTEN IN ADVANCE OF THE TROUGHING MOVING THROUGH THE PLAINS STATES. DURING THE DAY ON SUNDAY...THE IMPACTS FROM THIS WILL BE RELATIVELY MINOR...WITH LITTLE TO NO CHANGE IN SURFACE FLOW. HOWEVER...WITH TEMPERATURES BEGINNING TO WARM ALOFT...SIGNIFICANT BREAKS IN THE CLOUDS ARE FINALLY EXPECTED TO DEVELOP. WITH SUN...TEMPERATURES WILL BE ABLE TO RISE 5-8 DEGREES FROM SATURDAY TO SUNDAY...ESPECIALLY IN THE SOUTHERN CWA (WHERE CLOUDS SHOULD ERODE MORE QUICKLY). AS MONDAY BEGINS...STRENGTHENING SSW 850MB WINDS WILL BEGIN TO FEED MOISTURE INTO THE MIDDLE OHIO VALLEY. ON THE NOSE OF THE MOISTURE PUSH...WEAK ISENTROPIC ASCENT WILL ALLOW FOR THE POSSIBILITY OF SOME LIGHT SHOWERS. FOLLOWING PROBABILITY PLOTS FROM THE 15Z SREF...IT APPEARS THAT ANYTHING THAT DEVELOPS WILL MOVE NORTHEAST THROUGH THE CWA BETWEEN 12Z AND 21Z...AND WILL NOT BE DIRECTLY ASSOCIATED WITH THE IMPENDING LARGE-SCALE ACTIVITY STILL FAR OFF TO THE WEST. COMING OUT OF ANOTHER COOL OVERNIGHT PERIOD...PRECIPITATION TYPE AT ONSET WOULD BE SOMEWHAT IN QUESTION...BUT ANY AMOUNTS ARE EXPECTED TO BE VERY LIGHT. ONLY A 20-PERCENT CHANCE WAS ADDED TO THE FORECAST. A SUBSTANTIAL WARMING IS EXPECTED ON MONDAY...AS LOW-LEVEL FLOW MAKES THE SWITCH TO THE SOUTH (SSW AT 850MB AND SSE AT THE SURFACE). A SLIGHT UPWARD ADJUSTMENT WAS MADE FROM THE PREVIOUS FORECAST...WITH LOWER 50S NOW EXPECTED IN THE FAR SOUTHERN CWA. STRENGTHENING FLOW WILL KEEP TEMPERATURES FROM FALLING MUCH ON MONDAY NIGHT...AND NON-DIURNAL TEMPERATURES WERE REQUIRED FOR THE FORECAST GRIDS. WITH A SLOWING IN THE MODEL TRENDS FOR THE PROGRESSION FOR THE NEXT SYSTEM...POPS WERE REDUCED FOR THE MONDAY NIGHT PERIOD...WITH THE ONSET OF WIDESPREAD PRECIPITATION APPEARING LIKELY TO HOLD OFF UNTIL TUESDAY. && .LONG TERM /TUESDAY THROUGH SATURDAY/... HAVE USED A BLEND OF THE 12Z ECMWF AND WPC GUIDANCE FOR THE LONG TERM FORECAST. THE ECMWF IS FASTER...DEEPER...BUT MORE QUICK TO TAKE STRONG LOW PRESSURE FROM THE OHIO VALLEY REGION TUESDAY NIGHT TO SOUTHERN ONTARIO BY THURSDAY MORNING. THE GFS IS SLOWER...NOT AS DEEP...AND ROTATES MORE OF A SFC TROUGH THROUGH THE REGION ON THURSDAY/CHRISTMAS. THE ECMWF/WPC BLEND IS PREFERRED AT THIS TIME. AN UPPER TROUGH IS FORECAST TO PIVOT AND BECOMES NEGATIVELY TILTED AS IT LIFTS THROUGH THE OHIO VALLEY TUESDAY NIGHT INTO WEDNESDAY. THIS SCENARIO WILL EVENTUALLY PUSH SURFACE LOW PRESSURE AND COLD FRONT ACROSS THE FORECAST AREA. ABOVE NORMAL TEMPERATURES ARE EXPECTED AHEAD OF THE SYSTEM WITH TEMPERATURES COOLING OFF TOWARD MORE SEASONAL NORMALS IN CAA BEHIND THE COLD FRONT. IN TERMS OF PCPN CHANCES...THEY ARE EXPECTED TO STEADILY INCREASE AS FORCING GETS CLOSER/STRONGER BY TUESDAY NIGHT INTO WEDNESDAY MORNING. AM EXPECTING RAIN SHOWERS ACROSS THE ENTIRE AREA TUESDAY INTO TUESDAY NIGHT. COVERAGE WILL DECREASE SOME ON WEDNESDAY AS THE STRONGEST LIFT MOVES NORTHEAST. THERE IS SOME EVIDENCE THAT SOME EMBEDDED THUNDER MAY OCCUR WITH THIS SYSTEM...BUT HAVE DECIDED TO HOLD OFF THE MENTION ATTM. COLDER AIR COMING IN ON THE BACK SIDE OF THE SYSTEM WILL CAUSE A CHANGE OVER TO SOME SNOW SHOWERS LATER WEDNESDAY INTO WEDNESDAY NIGHT. SNOW SHOWERS WILL TAPER OFF BY THURSDAY MORNING/CHRISTMAS. CONSIDERING THE WARMER AIR AHEAD OF THE SYSTEM AND TEMPERATURES BOTTOMING OUT MAINLY IN THE 30S BY THURSDAY MORNING...AM ONLY EXPECTING MINOR SNOW ACCUMULATIONS WITH THE SNOW SHOWER ACTIVITY. IT APPEARS THE BIGGEST IMPACT WITH THIS WEATHER SYSTEM WILL BE THE WIND. HOWEVER...WITH THE ECMWF SOLUTION...THE STRONGEST WINDS MAY REMAIN NORTH OF OUR AREA WEDNESDAY NIGHT. RIDGING DEVELOPS RATHER QUICKLY LATE THURSDAY AND MOVES EAST THURSDAY NIGHT. THIS WILL ALLOW FOR MODEST WARM AIR ADVECTION AHEAD OF THE NEXT LOW PRESSURE SYSTEM AND COLD FRONT THAT WILL APPROACH THE REGION ON FRIDAY. THE COLD FRONT WILL SLOWLY MOVE THROUGH THE AREA FRIDAY NIGHT AND SATURDAY. WILL CONTINUE WITH A CHANCE OF RAIN SHOWER AHEAD OF THE COLD FRONT WITH PERHAPS A BRIEF MIX WITH OR CHANGE OVER TO SOME SNOW SHOWERS BEFORE TAPERING OFF ON SATURDAY. TEMPERATURES WILL REBOUND AGAIN ON FRIDAY AND THEN COOL OFF TOWARD SEASONAL NORMALS BY SATURDAY. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... MVFR CLOUD DECK CONTINUES TO BLANKET THE REGION. A FEW HOLES HAVE DEVELOPED IN IT FROM TIME TO TIME...BUT THEY HAVE FILLED BACK IN. AS THE CENTER OF HIGH PRESSURE BEGINS TO SLIP EASTWARD LATE TONIGHT...DRIER LOW LEVEL AIR FROM CENTRAL KY WILL WORK INTO THE TRI-STATE. EXPECT THE CVG/LUK TAFS TO BE THE FIRST TO GO VFR...IN THE 08-09Z TIME RANGE. AS SUNDAY PROGRESSES THE DRIER AIR WILL GRADUALLY WORK NORTHWARD...ALLOWING KDAY TO EXPERIENCE THE VFR CONDITIONS. IT IS LOOKING LIKE THE CENTRAL OHIO TAFS WILL BE THE LAST PLACE THE DRIER AIR WORK IN...SO EXPECT THE MVFR CONDITIONS TO LINGER PAST 18Z. OUTLOOK...MVFR/IFR CEILINGS AND VISIBILITIES ARE POSSIBLE TUESDAY INTO THURSDAY...ALONG WITH WINDY CONDITIONS. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...NONE. KY...NONE. IN...NONE. && $$ SYNOPSIS...HATZOS NEAR TERM...HATZOS SHORT TERM...HATZOS LONG TERM...HICKMAN AVIATION...SITES

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