MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1224 PM EDT SUN APR 02 2017 VALID APR 02/1200 UTC THRU APR 06/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES... LOW PRESSURE MOVING FROM TEXAS TO NEW ENGLAND... PREFERENCE: HALFWAY BETWEEN THE GFS AND 00Z ECMWF CONFIDENCE: BEFORE 00Z WED...AVERAGE AFTER 00Z WED...SLIGHTLY BELOW AVERAGE MODELS ARE QUITE CLOSE AS THE LOW TRACKS INTO THE GREAT LAKES. AFTERWARD...THE NAM AND GFS HAVE TRENDED A LITTLE SOUTHWARD WITH THE LOW REFORMING IN THE GULF OF MAINE AND SLIGHTLY SLOWER WITH THE SECONDARY LOW PERSISTING ACROSS NORTHERN NEW YORK, RESULTING IN SOLUTIONS THAT ARE A BIT DIFFERENT FROM THE 00Z ECMWF, WHICH IS WEAKER INLAND AND NORTH OF THE NAM/GFS IN THE GULF OF MAINE. GIVEN MODEST SOLUTION SPREAD OWING TO TIMING DIFFERENCES AS WELL AS UNCERTAINTIES WITH THE FLOW ACROSS CANADA, AN INTERMEDIATE SOLUTION INVOLVING THESE 2 DIFFERENT SOLUTIONS IS RECOMMENDED. THE NAM COULD BE USED AS AN ALTERNATIVE TO THE GFS ACROSS NEW ENGLAND, YET ITS SENSIBLE WEATHER DETAILS MAY BE LESS ACCURATE. SHORTWAVE TROUGH SPLITTING OVER THE INTERMOUNTAIN WEST MON-TUE... LOW PRESSURE MOVING FROM THE S. PLAINS TO MID MS VALLEY TUE-WED... PREFERENCE: 2/3 GFS TO 00Z 1/3 ECMWF CONFIDENCE: BEFORE 12Z TUE...AVERAGE AFTER 12Z TUE...BELOW AVERAGE SOLUTIONS ARE LARGELY SIMILAR UNTIL TUE, WHEN THE NAM MOVES TOWARD THE FAST SIDE OF THE GUIDANCE, AND THUS IS NOT RECOMMENDED AFTER TUE, WITH THE GFS CLOSEST TO THE CONSENSUS, AND 00Z ECMWF WITHIN THE SLOWEST 1/4 OF ALL SOLUTIONS. MODEL TRENDS SINCE YESTERDAY ARE FASTER, WHICH SUPPORTS THE GFS SIDE OF THE ENVELOPE. BEYOND TUE THOUGH, THE ENVELOPE BECOMES QUITE LARGE, PARTICULARLY WITH HOW THE NORTHERN STREAM FLOW EVOLVES NORTH OF THE LOW. FOR THESE REASONS, RECOMMEND A SOLUTION THAT LEANS TOWARD THE GFS, WITH A MINORITY OF THE SLOWER ECMWF ALSO USED IN A BLEND TO ADDRESS UNCERTAINTY. LEADING EDGE OF LONGWAVE TROUGH NEARING THE NORTHWEST WED... PREFERENCE: MODEL CONSENSUS CONFIDENCE: ABOVE AVERAGE MODEL SOLUTIONS ARE QUITE CLOSE TO EACH OTHER, WHICH IS CONSISTENT WITH THE TROUGH'S SIZE, WHICH IS LIKELY WELL-INITIALIZED. THE NAM AND 00Z ECMWF ARE SLIGHTLY FASTER THAN THE GFS, WITH DIFFERENCES ON THE ORDER OF 6 HOURS OR LESS FOR A DAY 3 PREDICTION. GIVEN THE 00Z PARALLEL GFS IS ABOUT MIDWAY BETWEEN THESE 2 SPEEDS, AN INTERMEDIATE SOLUTION APPEARS LIKE A GOOD BEGINNING. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES