MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 202 PM EST WED DEC 23 2015 VALID DEC 23/1200 UTC THRU DEC 27/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LOW PRESSURE TRACKING THROUGH THE UPPER GREAT LAKES TONIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODELS SHOW SIMILARLY WITH THIS SYSTEM. LOW AMPLITUDE SHORTWAVE REACHING THE CNTRL PLAINS THU MORNING POSSIBLE LOW PRESSURE OVER THE C. PLAINS THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 12Z UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE THERE ARE SOME DIFFERENCES WITH THE PLACEMENT OF THIS LOW...WITH ENSEMBLE PLOTS RANGING FROM THE CNTRL TEXAS PANHANDLE TO N-CNTRL OKLAHOMA FOR 12Z/24. THERE ARE ALSO HINTS IN THE GUIDANCE FOR A WEAKER LOW AT THE SAME TIME IN NRN KANSAS OR NEBRASKA. THE 12Z NAM REMAINS THE STRONGEST WITH THIS FEATURE AND IS NOT SUPPORTED BY THE LATEST ENSEMBLE LOW PLOTS STARTING 00Z/25. THERE ARE SUBTLE DIFFERENCES WITH THE MID-LEVEL SHORTWAVE...WITH THE 12Z GFS/12Z UKMET CONTINUE TO SHOW CLOSEST TO THE MIDDLE OF THE LATEST DETERMINISTIC/ENSEMBLE SPREAD. THE 12Z ECMWF IS MORE DEFINED WITH THE SURFACE LOW COMPARED TO ITS PREVIOUS RUN BUT REMAINS WEAKER THAN THE CONSENSUS. FRONTAL BOUNDARY DRAPED FROM THE NORTHEAST TO THE LOWER MISSISSIPPI VALLEY THU-FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET CONFIDENCE: BELOW AVERAGE THE 12Z GFS IS ON THE SOUTH SIDE OF ALL THE GUIDANCE ACROSS THE OHIO/TENNESSEE VALLEYS...WHILE THE REMAINING DETERMINISTIC/ENSEMBLE GUIDANCE IS NORTH. RUN TO RUN CONSISTENCY IN THE GUIDANCE IS GOOD...SO THERE ARE NO SIGNIFICANT TRENDS TO DOCUMENT. THE ENSEMBLE MEANS REMAIN SUPPORTIVE OF A 12Z ECMWF/UKMET BLEND REGARDING THE LATITUDE OF THE FRONT ON THU/FRI. HOWEVER...GIVEN THE SIGNIFICANT DIFFERENCES AND RELATIVE EARLY NATURE OF THE FORECAST...CONFIDENCE IS BELOW AVERAGE. UPPER TROUGH EVOLVING OVER THE GREAT BASIN/S. ROCKIES THU-SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z/00Z ECMWF OR NEAR THE 00Z ECMWF ENSEMBLE MEAN CONFIDENCE: AVERAGE THERE IS DECENT ENSEMBLE SUPPORT WITH THIS FEATURE GIVEN SOME TRENDS TOWARD A COMMON POSITION OF THE UPPER TROUGH...AS THE SYNOPTIC SCALE DIFFERENCES AMONG THE LATEST DETERMINISTIC MODELS IS SMALL BY SAT. HOWEVER...DETAILS OF SMALLER SCALE WAVES WITHIN THE LARGER SCALE TROUGH DIFFER. REGARDING A SHORTWAVE AT THE LEADING EDGE OF THE UPPER TROUGH...PROGGED TO REACH THE PLAINS EARLY SAT MORNING. THE 12Z UKMET REMAINS A BIT MORE PROGRESSIVE THAN THE CONSENSUS BUT HAS SLOWED FROM ITS 00Z RUN. THE 12Z GFS IS STRONGEST AND MOST NORTH REGARDING A WEAK SURFACE LOW OR INVERTED TROUGH TO THE NORTH...WHICH SEEMS COUNTER-INTUITIVE GIVEN THE PRESENCE OF HIGH PRESSURE ACROSS THE N-CNTRL CONUS. THE ECMWF/ECMWF REMAIN THE MOST LIKELY SOLUTION GIVEN THEIR PROXIMITY TOWARD THE ENSEMBLE CONSENSUS ALOFT AND AT THE SURFACE. REGARDING THE POWERFUL CLOSED MID-LEVEL LOW ACROSS THE SOUTHWEST...ENSEMBLE SPAGHETTI HEIGHTS APPEAR TO BE CLUSTERED BEST OVER SERN ARIZONA BY 00Z/27. WHILE THE ECMWF IS IN AGREEMENT WITH THE ENSEMBLE POSITION...ALL OF THE LATEST DETERMINISTIC MODELS SHOW SIMILARLY HERE WITH ONLY MINOR PLACEMENT DIFFERENCES. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO