MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1219 AM EST TUE DEC 08 2015 VALID DEC 08/0000 UTC THRU DEC 11/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION INCLUDING PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED UPPER LEVEL LOW PASSING OVER SRN NEW ENGLAND THIS MORNING DEVELOPING SURFACE LOW IN THE WRN ATLANTIC TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/12Z ECMWF/12Z UKMET BLEND CONFIDENCE: ABOVE AVERAGE TIGHT SURFACE LOW ENSEMBLE CLUSTERING EXISTS IN THE 12Z/07 SUITE...WITH THE 00Z NAM...00Z GFS...12Z ECMWF AND 12Z UKMET MATCHING QUITE NICELY. THE BIGGEST DIFFERENCE BETWEEN THESE MODELS IS THEIR STRENGTH WITH THE 00Z GFS WEAKEST. THE 12Z CMC IS SOUTH OF THE REMAINING MODEL CLUSTERING. ENSEMBLE AND DETERMINISTIC CLUSTERING SUPPORTS A STRONGER LOW THAN THE 00Z GFS...SO IT IS NOT INCLUDED IN THE PREFERENCE. SHORTWAVE NEAR LAKE MICHIGAN EARLY THIS MORNING AND LIFTING ACROSS NEW ENGLAND BY WED MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM...00Z GFS...12Z ECMWF BLEND CONFIDENCE: ABOVE AVERAGE SIMILAR TO YESTERDAY...THE NAM/GFS/ECMWF SHOW GOOD AGREEMENT TO EACH OTHER WITH THIS FEATURE WHILE THE 12Z UKMET REMAINS STRONGER/SOUTH WITH THIS SHORTWAVE AS IT REACHES THE NORTHEAST U.S. THE 12Z CMC ENDS UP THE FLATTEST WITH THE SHORTWAVE AS IT TRACKS NORTHEASTWARD. THE GOOD AGREEMENT OF THE NAM/GFS/ECMWF AND GOOD RUN TO RUN CONTINUITY OF THESE MODELS SUPPORT THEIR PREFERENCE. SHORTWAVE AMPLIFYING ACROSS THE CNTRL U.S. TUE NIGHT AND REACHING THE EAST COAST THU MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/12Z ECMWF BLEND CONFIDENCE: BELOW AVERAGE ENSEMBLE TRENDS WITH THIS SHORTWAVE SHOW SIGNIFICANT SLOWING VALID 00Z/10 ACROSS THE APPALACHIANS...LED BY THE 12Z GEFS...WITH THE 12Z ECMWF/12Z UKMET FOLLOWING SUIT COMPARED TO RUNS FROM 24 HOURS AGO. HOWEVER...THE 18Z GEFS MEAN HAS COME BACK TO A MORE PROGRESSIVE IDEA BY 00Z/10...WHICH LEAVES THE 12Z ECMWF ON THE SLOWER/DEEPER EDGE OF THE ENSEMBLES. THE 12Z UKMET IS ALSO DEEP BUT PUTS THE EMPHASIS OF THE SHORTWAVE ACROSS THE SRN END...AND THE 12Z UKMET IS UNIQUE IN HAVING A SEPARATE PIECE OF THE TROUGH BREAK OFF AND TRACK TO THE NORTH CAROLINA COAST BY THU MORNING. GIVEN THE UNCERTAINTY AND POOR RUN TO RUN CONSISTENCY SEEN IN SOME OF THE MODELS...WE PREFER TO GO TOWARD THE MIDDLE OF THE SPREAD WHICH HAPPENS TO BE NEAR THE STABLE 00Z GFS...WHICH HAS SHOWN LITTLE CHANGES FROM ITS 12Z/07 AND 00Z/07 RUNS. HOWEVER...GIVEN THE ENSEMBLE SPREAD...WILL BLEND THE 00Z GFS WITH THE 12Z ECMWF...WHICH OFFERS A SLOWER/DEEPER TRACK TO THE 00Z GFS. THE 12Z EC MEAN IS ALSO BETWEEN THE 00Z GFS AND 12Z ECMWF. LOW AMPLITUDE SHORTWAVE/SURFACE LOW NEARING THE PACIFIC NORTHWEST WED MORNING AND SHIFTING ACROSS TO THE NORTHERN TIER AND UPPER MIDWEST BY THU NIGHT SURFACE LOW ACROSS THE UPPER MIDWEST THU NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z UKMET / 12Z EC MEAN BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE A MODEST DEGREE OF ENSEMBLE SPREAD REMAINS WITH THIS SHORTWAVE BY 00Z/11 ACROSS THE MISSISSIPPI VALLEY...BUT THE MEANS SHOW SIMILARLY. WILL GO TOWARD THE MIDDLE/MEANS BEST REPRESENTED BY A BLEND OF THE 00Z GFS AND 12Z ECMWF....OR NEAR THE 12Z UKMET. THE 12Z EC MEAN IS ALSO BETWEEN THE 00Z GFS/12Z ECMWF BUT IS A BIT SOUTH AND SLOWER THAN THE 12Z UKMET WHICH IS A DECENT COMPROMISE. STRENGTHENING CLOSED LOW/UPPER TROUGH APPROACHING THE WEST COAST WED NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM..00Z GFS...12Z ECMWF BLEND CONFIDENCE: AVERAGE MODEL DIFFERENCES ARE NOT VERY LARGE BY FRI MORNING REGARDING THE TIMING/DEPTH OF A TROUGH AMPLIFYING OVER THE WRN U.S. AND SO THE PREFERENCE IS FOR A BLEND OF THE MODELS WHICH HAVE THE BEST AGREEMENT TO THE MEANS. CONFIDENCE COULD BE HIGHER GIVEN THE OVERALL TROUGH IS WELL HANDLED BUT THE INNER CORE DETAILS ARE YET TO BE IRONED OUT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO