MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1208 AM EDT MON MAY 25 2015 VALID MAY 25/0000 UTC THRU MAY 28/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. NORTHWEST U.S. CUT OFF LOW SHORTWAVE LIFTING INTO THE GREAT LAKES WEDNESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CANADIAN COMPROMISE CONFIDENCE: ABOVE AVERAGE BY LATE WEDNESDAY, THE 12Z CANADIAN BECOMES A SLOW/DEEP OUTLIER WITH BOTH OF THESE SYSTEMS -- ITS USUAL BIAS. PREFER THE CONSENSUS OF THE 00Z NAM/00Z GFS/12Z ECMWF/12Z UKMET WITH ABOVE AVERAGE CONFIDENCE. SHORTWAVE MOVING INTO THE OH VALLEY WEDNESDAY NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: WEAK VERSION OF THE 00Z NAM CONFIDENCE: SLIGHTLY BELOW AVERAGE BY WEDNESDAY NIGHT, THE GUIDANCE SHOWS SOME DISPERSION WITH THIS SYSTEM, AS THE 00Z GFS IS THE QUICKEST -- ITS USUAL BIAS -- WHILE THE 12Z ECMWF/12Z UKMET ARE THE SLOWEST. THE 12Z ECMWF/18Z GEFS MEAN SOLUTIONS SUPPORT THEIR DETERMINISTIC RUNS. TO ACCOUNT FOR THE SPREAD, PREFER A WEAK VERSION OF THE INTERMEDIATE 00Z NAM WITH SLIGHTLY BELOW AVERAGE CONFIDENCE. SHORTWAVE LIFTING FROM GREAT PLAINS INTO GREAT LAKES BY MONDAY NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: ECMWF/UKMET/CANADIAN COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z NAM/00Z GFS LAG THE REMAINDER OF THE GUIDANCE WITH THIS FEATURE AS IT STREAKS NORTHWEST/NORTH OF MAINE. SINCE THE PARENT SHORTWAVE IS SHEARING OUT WITHIN A CONFLUENT FLOW PATTERN, AND THE QUICKER GUIDANCE HAS THE SUPPORT OF THE 12Z ECMWF/18Z GEFS MEANS, PREFER A COMPROMISE OF THE 12Z ECMWF/12Z UKMET/12Z CANADIAN. HAVE LOWERED CONFIDENCE FROM EARLIER, IN CASE THE SHIFT SEEN IN THE NAM/GFS SIGNALS A TREND THAT COULD BECOME COMMON AMONGST THE 00Z GUIDANCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ROTH