MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 243 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 MODEL GUIDANCE ALONG WITH FINAL 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-00Z 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 00Z GEFS MEAN) AS IT FLATTENS OUT. THE 00Z ECMWF MAINTAINED ITS TIMING (SUPPORTED BY THE 12Z ECMWF ENSEMBLE MEAN)...WHICH WAS A BIT FASTER THAN THE 00Z GFS. THE 00Z UKMET CONTINUES TO BE THE WESTERNMOST MEMBER OF THE SOLUTION ENVELOPE...AND REMAINS OUTSIDE OF THE PREFERENCE BECAUSE OF THIS. ...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/00Z UKMET/00Z ECMWF BLEND CONFIDENCE: SLIGHTLY ABOVE 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 AFTER 23/00Z. HOWEVER...THE 00Z ECMWF/00Z UKMET AND THE 00Z GEFS MEAN SPED UP THEIR RESPECTIVE SOLUTIONS...SO THAT THE 00Z GFS IS NO LONGER AN EASTERN OUTLIER. BECAUSE OF THE BETTER CLUSTERING WITH THE PLACEMENT OF THE LONG WAVE TROUGH BY 23/12Z...THE 00Z UKMET CAN BE ADDED TO THE PREFERENCE...WHICH INCREASES FORECAST CONFIDENCE SLIGHTLY. ...NEGATIVELY TILTED LONG WAVE TROUGH REACHING THE PACIFIC NORTHWEST LATE FRI NIGHT/SAT... PREFERENCE: 00Z GFS/00Z ECMWF 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 FROM THE 00Z GEFS AND 12Z ECMWF ENSEMBLE MEAN)...THOUGH IT MAY BE A TAD TOO SLOW BY THE END OF THE PERIOD. THE 00Z UKMET SLOWED ITS PLACEMENT OF THE LONG WAVE TROUGH...SO IT WAS ADDED TO THE PREFERENCE. ADDING THE 00Z UKMET TO THE PREFERENCE INCREASED FORECAST CONFIDENCE SLIGHTLY. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ HAYES