MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1235 AM EDT THU APR 20 2017 VALID APR 20/0000 UTC THRU APR 23/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... AN EVALUATION OF THE 00Z 00Z NAM/GFS ALONG WITH INITIAL PREFERENCES AND FORECAST CONFIDENCE ...SHORT WAVE OVER THE GREAT LAKES MOVING THROUGH NEW ENGLAND TODAY... PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 00Z NAM/GFS REMAIN IN LOCK STEP WITH THE REMAINDER OF THE GUIDANCE SHOWING THE SHORT WAVE TRACKING ACROSS NEW ENGLAND DURING THE FIRST HALF OF TODAY. A GENERAL MODEL BLEND IS RECOMMENDED WITH ABOVE AVERAGE CONFIDENCE. ...DEEPENING LONG WAVE TROUGH CROSSING THE GREAT LAKES/OH VALLEY TODAY AND NEW ENGLAND FRI,,, ...DEVELOPING SURFACE LOW AND FRONTAL BOUNDARY OVER THE GREAT LAKES/OH VALLEY TODAY...TRACKING INTO NEW ENGLAND FRI... PREFERENCE: NON-12Z UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z NAM REMAINS IN GOOD AGREEMENT WITH THE MODEL CONSENSUS TAKING THE LONG WAVE TROUGH OVER THE GREAT LAKES FRI AND NEW ENGLAND SAT...BUT THE 00Z GFS BECOMES A BIT SLOWER THAN THE CONSENSUS AS IT TRACKS ACROSS NEW ENGLAND SAT (EVEN SLOWER THAN THE 12Z GEFS MEAN) AS IT FLATTENS OUT. OTHERWISE...THERE IS FAIRLY GOOD MODEL CLUSTERING (ASIDE FROM THE 12Z UKMET...WHICH IS SLOWER THAN EVEN THE 00Z GFS WITH THE LONG WAVE TROUGH)...SO A NON 12Z UKMET BLEND IS PREFERRED. ...LONG WAVE TROUGH MOVING ACROSS THE WEST TODAY...CLOSING OFF OVER THE CENTRAL/SOUTHERN PLAINS FRI...AND CROSSING THE MIDDLE/LOWER MS VALLEY SAT... PREFERENCE: 00Z GFS/12Z ECMWF BLEND CONFIDENCE: AVERAGE THE 00Z NAM IS CLOSE TO THE MODEL CONSENSUS WITH RESPECT TO THE TIMING OF THE MID LEVEL SYSTEM CLOSING OFF OVER THE SOUTHERN PLAINS...BUT REMAINS STRONGER THAN THE REMAINDER OF THE MODEL CONSENSUS WITH THE CLOSING MID LEVEL SYSTEM OVER THE LOWER MS VALLEY AFTER 22/12Z. THE 00Z GFS IS ALSO CLOSE TO THE MODEL CONSENSUS WITH THE MID LEVEL TROUGH OVER THE LOWER AND MID MS VALLEY...BUT BECOMES FASTER THAN THE CONSENSUS (AND THE 12Z GEFS MEAN) AFTER 23/00Z. IT IS NOT CLEAR IF THE 00Z GFS IS PICKING UP ON A TREND FOR A FASTER SOLUTION WITH THE LONG WAVE TROUGH...SO FOR NOW ITS REMAINS IN THE BLEND. HOWEVER...THE ECMWF HAS BEEN MORE CONSISTENT WITH THE TIMING OF THE LONG WAVE TROUGH...SO MORE WEIGHT WAS GIVEN TO THE 12Z ECMWF HERE. BECAUSE OF THE TIMING DIFFERENCES INTRODUCED BY THE 00Z GFS...FORECAST CONFIDENCE REMAINS AVERAGE. ...NEGATIVELY TILTED LONG WAVE TROUGH REACHING THE PACIFIC NORTHWEST LATE FRI NIGHT/SAT... PREFERENCE: 00Z GFS/12Z BLEND CONFIDENCE: AVERAGE THE 00Z NAM REMAINS ON THE EASTERN EDGE OF THE MODEL SOLUTION ENVELOPE CONCERNING THE TIMING OF THE CLOSING MID LEVEL LOW AS IT REACHES VANCOUVER ISLAND BY 23/12Z. BY CONTRAST...THE 00Z GFS REMAINS CLOSER TO THE MODEL CONSENSUS (BOLSTERED BY SUPPORT FORM THE 12Z GEFS AND 12Z ECMWF ENSEMBLE MEAN)...THOUGH IT MAY BE A TAD TOO SLOW BY THE END OF THE PERIOD. THE 12Z UKMET ALSO LOOKED A BIT DEEPER AND SLOWER...SO IT IS POSSIBLE THAT A SLOWING TREND IS OCCURRING WITH THE GUIDANCE. BECAUSE OF THE TIMING DIFFERENCES...FORECAST CONFIDENCE REMAINS AVERAGE. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ HAYES