MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1108 PM EST THU JAN 01 2015 VALID JAN 02/0000 UTC THRU JAN 05/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. PACIFIC NORTHWEST SUNDAY/MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-GFS COMPROMISE CONFIDENCE: ABOVE AVERAGE PROBLEMS IN THIS REGION STEM FROM A DEEP CYCLONE MOVING FROM THE NORTHEAST PACIFIC OVER THE TOP OF THE WESTERN RIDGE. THE 00Z GFS BREAKS DOWN THE RIDGE MUCH FASTER THAN THE OTHER GUIDANCE, STEERING THE DEEP CYCLONE DUE EASTWARD. THIS IS A BIAS SOMETIMES SEEN IN THE DETERMINISTIC GUIDANCE. THE PREFERENCE IS FOR A NAM/ECMWF/UKMET/CANADIAN COMPROMISE, WHICH HAS THE SUPPORT OF THE 12Z/18Z/21Z RUNS OF THE ECMWF/GEFS/SREF ENSEMBLE MEANS, WHICH ARE IN GOOD AGREEMENT. BROAD CYCLONE MOVING INTO THE MIDWEST SAT/SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/ECMWF/NAM COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 12Z UKMET/00Z NAM BRING TOO MUCH (OR ENERGY ALOFT WHICH IS TOO STRONG) INTO THE MIDWEST FRIDAY NIGHT. LUCKILY, THE ISSUES ALOFT AT 500 HPA AND 700 HPA HAVE MINIMAL BEARING ON THE PRESSURE DISTRIBUTION ACROSS THE REGION. OTHERWISE, A SECOND NORTHERN STREAM SHORTWAVE INTERACTS WITH THE CLOSED LOW MOVING OUT OF THE SOUTHWEST TO PRODUCE A HEALTHY CYCLONE MOVING ACROSS MI SAT NIGHT/SUN MORNING. THE 21Z SREF MEAN BECOMES TOO OPEN ALOFT AND TOO QUICK WITH ITS DEPICTION OF THE MAIN SURFACE LOW AS SOON AS LATE SATURDAY. THE 00Z GFS/00Z NAM/12Z ECMWF ARE CLOSEST TO THE 12Z/18Z RUNS OF THE ECMWF/GEFS/SREF ENSEMBLE MEANS, AND A COMPROMISE OF THE THREE ARE PREFERRED WITH ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ROTH