MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 229 AM EDT THU MAY 21 2015 VALID MAY 21/0000 UTC THRU MAY 24/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION WITH PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. COMPLEX WESTERN GYRE ~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM COMPROMISE CONFIDENCE: ABOVE AVERAGE MASS FIELD-WISE, THE 00Z NAM BECOMES A STRONG OUTLIER WITH ONE DISTURBANCE IN WY SATURDAY NIGHT/SUNDAY MORNING, WHICH CAUSES ITS SURFACE LOW IN THE PLAINS TO LIFT MORE NORTHWEST THAN THE REMAINDER OF THE GUIDANCE (WHICH ONLY HAS THE SUPPORT OF A FEW OF THE 90 12Z GLOBAL ENSEMBLE MEMBERS). A COMPROMISE OF THE 00Z GFS/00Z UKMET/00Z CANADIAN/00Z ECMWF FITS THE 12Z ECMWF/00Z GEFS MEANS THE BEST, WHICH IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE. THESE MASS FIELD PREFERENCES MAY NOT BE IDEAL FOR THE QPF PATTERN, HOWEVER. FOR QPF PREFERENCES DOWNSTREAM IN THE WATERLOGGED SOUTHERN PLAINS, SEE OUR QPF GRAPHICS AND DISCUSSION FOR MORE DETAILS. SYSTEMS MOVING THROUGH THE NORTHEAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE SHOWS GOOD AGREEMENT IN THIS REGION. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ROTH