MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 204 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 MODEL EVALUATION INCLUDING FINAL MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED UPPER LEVEL LOW PASSING OVER SRN NEW ENGLAND THIS MORNING DEVELOPING SURFACE LOW IN THE WRN ATLANTIC TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z GFS COMPROMISE CONFIDENCE: ABOVE AVERAGE TIGHT SURFACE LOW ENSEMBLE CLUSTERING EXISTS IN THE 12Z/07 SUITE...WITH THE 00Z NAM/GFS/ECMWF/UKMET/CMC MATCHING POSITION QUITE NICELY. THE BIGGEST DIFFERENCE BETWEEN THESE MODELS IS THEIR STRENGTH WITH THE 00Z GFS WEAKEST. 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: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 00Z UKMET/CMC TRENDED TOWARD THE GOOD AGREEMENT/CONTINUITY OF THE NAM/GFS/ECMWF. WITH THIS ADJUSTMENT...THERE IS ENOUGH AGREEMENT AMONG THE LATEST GUIDANCE TO PREFER A GENERAL MODEL COMPROMISE. SHORTWAVE AMPLIFYING ACROSS THE CNTRL U.S. TUE NIGHT AND REACHING THE EAST COAST THU MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/00Z 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/00Z GEFS MEANS HAVE COME BACK TO A MORE PROGRESSIVE IDEA BY 00Z/10...WHICH LEAVES THE 12Z ECMWF ON THE SLOWER/DEEPER EDGE OF THE ENSEMBLES. THE 00Z UKMET REMAINS SOMEWHAT SIMILAR TO ITS PREVIOUS RUN WITH PUTTING THE EMPHASIS ON THE SRN END OF THE SHORTWAVE TROUGH...BREAKING OFF A SEPARATE PIECE OF THE TROUGH TOWARD THE NORTH CAROLINA COAST BY THU MORNING. THE 00Z ECMWF ADJUSTED VERY SIMILARLY TO THE 00Z GFS...BUT GIVEN THE UNCERTAINTY AND POOR RUN TO RUN CONSISTENCY SEEN IN SOME OF THE MODELS...WE PREFER TO GO TOWARD THE MIDDLE OF THE LATEST SPREAD WHICH HAPPENS TO BE NEAR THE STABLE 00Z GFS...WHICH HAS SHOWN LITTLE CHANGES FROM ITS 12Z/07 AND 00Z/07 RUNS. THE ENSEMBLE MEANS HOWEVER...ARE SLIGHTLY SLOWER THAN THE GFS/ECMWF COMBO. 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: 00Z UKMET / 00Z ECMWF 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 UKMET. THE 00Z ECMWF ADJUSTED NORTH AND IS INCLUDED IN THE PREFERENCE NOW. THE 12Z EC MEAN IS ALSO BETWEEN THE 00Z GFS/12Z ECMWF. STRENGTHENING CLOSED LOW/UPPER TROUGH APPROACHING THE WEST COAST WED NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z CMC 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. THE 00Z CMC STANDS OUT THE MOST FROM THE RELATIVE GOOD AGREEMENT...IN THAT THE CMC HAS A HIGHER HEIGHTS DOWNSTREAM ACROSS THE ROCKIES AT THE END OF THE SHORT RANGE PERIOD...12Z/11. CONFIDENCE COULD BE HIGHER GIVEN THE OVERALL TROUGH IS WELL HANDLED BUT THE INNER CORE DETAILS HAVE YET TO BE IRONED OUT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO