MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 208 AM EST SUN DEC 06 2015 VALID DEC 06/0000 UTC THRU DEC 09/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED LOW TRACKING ACROSS THE OHIO VALLEY MON AND EXITING INTO THE WRN ATLANTIC FOR TUE DEVELOPING SURFACE LOW IN THE WRN ATLANTIC BY TUE MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/00Z ECMWF/00Z CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE DIFFERENCES ARE BECOMING SMALLER WITH SUBSEQUENT MODEL RUNS SUCH THAT CONFIDENCE HAS INCREASED RELATIVE TO FRI NIGHT. SPREAD IN THE ENSEMBLE SPAGHETTI HEIGHTS CONTINUES TO SHOW A FAIR DEGREE OF TIMING/AMPLITUDE UNCERTAINTY BY THU MORNING OVER THE WRN ATLANTIC. HOWEVER...THE GFS/ECMWF HAVE TRENDED TOWARD ONE ANOTHER AND HAVE AGREEMENT WITH THE 00Z CMC...WITH THESE 3 MODELS FITTING IN THE MIDDLE OF THE BEST ENSEMBLE CLUSTERING. THE 00Z UKMET ADJUSTED NORTH WITH THE TRACK OF THE SHORTWAVE COMPARED TO ITS MORE FAVORABLE...PREVIOUS RUN...AND NO LONGER HAS A SURFACE LOW REFLECTION IN LINE WITH THE PREFERRED GUIDANCE. SHORTWAVE ALONG THE WEST COAST THIS MORNING AND REACHING THE PLAINS ON MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/00Z ECMWF BLEND CONFIDENCE: BELOW AVERAGE THE POTENTIAL INTERACTION OF THIS SHORTWAVE WITH WEAKER WAVES TO ITS NORTH...AS IT CROSSES THE ROCKIES...INFLUENCES HOW THE EVOLUTION OF THE MID-LEVEL PATTERN WILL TAKE PLACE. RUN TO RUN CONTINUITY HAS BEEN POOR AND THE ENSEMBLE MEANS TEND TO WASH OUT THIS SMALL SCALE FEATURE AS IT CROSSES THE MISSISSIPPI. THEREFORE...THE IDEA IS TO GO TOWARD THE MIDDLE OF THE LATEST SPREAD...BEST REPRESENTED BY THE 00Z NAM AND 00Z ECMWF. BELOW AVERAGE CONFIDENCE EXISTS GIVEN THE POOR RUN-TO-RUN CONTINUITY AS OF LATE. COMPACT MID-LEVEL SHORTWAVE AND SURFACE LOW APPROACHING VANCOUVER ISLAND TONIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE DESPITE MINOR DIFFERENCES...THERE IS PRETTY GOOD AGREEMENT AMONG THE LATEST MODELS. LOW AMPLITUDE SHORTWAVE REACHING WASHINGTON/OREGON MON NIGHT AND AMPLIFYING INTO THE NORTHERN PLAINS TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS...12Z ECMWF...12Z EC MEAN BLEND CONFIDENCE: BELOW AVERAGE BETTER AGREEMENT IS SEEN IN THE 00Z MODELS WITH THE SHORTWAVE AMPLITUDE OFF OF THE NORTHWEST COAST MON MORNING WITH THE EXCEPTION OF THE 00Z CMC WHICH HAS A VERY DIFFERENT ORIENTATION COMPARED TO THE NAM/GFS/ECMWF/UKMET. BY TUE...THE 00Z NAM GETS WEAKER AND THE 00Z UKMET BEGINS TO PULL AHEAD OF THE PACK. THE SURFACE REFLECTION IS FORECAST TO DEVELOP QUICKLY...WITH DIFFERENCES GROWING DOWNSTREAM ACROSS THE PLAINS. THE NAM IS A FLAT OUTLIER HERE...WHILE THE 00Z GFS...00Z ECMWF...00Z UKMET ARE TOWARD THE STRONGER END OF THE ENSEMBLE GUIDANCE. THERE ARE SEVERAL ECMWF ENSEMBLE MEMBERS DEPICTING A SURFACE LOW IN THE VICINITY OF SRN WISCONSIN BY 12Z/09. THIS IS CLOSE TO THE 00Z GFS AND 00Z ECMWF...BUT SINCE THESE MODELS ARE TOWARD THE DEEPER EDGE OF THE ENSEMBLES...BLENDING WITH THE FLATTER 12Z EC MEAN SEEMS APPROPRIATE. THE QUICKER UKMET IS LEFT OUT OF THE PREFERENCE AT THIS TIME. STRONG GULF OF ALASKA CLOSED LOW WITH STRONG ZONAL FLOW AND EMBEDDED JET STREAKS/SHORTWAVES MOVING INTO PACIFIC NORTHWEST THROUGH WED MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: BELOW AVERAGE THE MODELS ARE BROADLY SIMILAR HERE BY WED MORNING...BUT TIMING/AMPLITUDE DIFFERENCES REMAIN WITH SHORTWAVES EMBEDDED WITHIN TIGHTLY PACKED MID-LEVEL HEIGHTS. CONFIDENCE REMAINS LOW IN THE DETAILS BUT NONE OF THE DETERMINISTIC MODELS APPEAR SIGNIFICANTLY FROM ONE ANOTHER. THE 00Z GFS IS LIKELY...BEING IN THE MIDDLE OF THE SOMEWHAT SLOWER NAM...SOMEWHAT FASTER ECMWF/UKMET AND SOMEWHAT FLATTER CMC. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO