MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 227 PM EDT TUE APR 19 2016 VALID APR 19/1200 UTC THRU APR 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE INTERVALS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. UPPER LOW APPROACHING THE WEST COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: CLOSEST TO THE ECMWF CONFIDENCE: AVERAGE THERE IS A BIT OF SPREAD ON THIS SYSTEM'S LATITUDE, WITH THE 06Z GFS ON THE SOUTHERNMOST SIDE OF THE DETERMINISTIC SPREAD AND THE 12Z GFS/00Z UKMET ON THE NORTH SIDE. THE SYSTEM IS ROLLING EASTWARD DOWNSTREAM OF A WEAK RIDGE, WHICH COULD ALLOW IT TO LOSE SOME LATITUDE. THE 12Z ECMWF WAS IN THE MIDDLE OF THE SPREAD, CLOSE TO ITS ENSEMBLE MEAN SOLUTION, AND FIT THE ABOVE IDEA REASONABLY WELL. PREFER A SOLUTION CLOSE TO THE 12Z ECMWF WITH AVERAGE CONFIDENCE. UPPER LOW/TROUGH MOVING FROM THE PLAINS INTO THE EAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/ECMWF/UKMET COMPROMISE CONFIDENCE: AVERAGE THE 12Z NAM CLOSES OFF A 500 HPA CYCLONE ACROSS THE LOWER MS/TN VALLEYS WHICH, ALBEIT SUPPORTED BY THE 06Z GEFS MEAN, DOES NOT BEFIT THE FLOW PATTERN IN WHICH IT IS EMBEDDED -- A BROAD RIDGE/BROAD DOWNSTREAM TROUGH CONFIGURATION. THE NAM'S SURFACE LOW LATE FRIDAY ALSO LIES OUTSIDE THE 00Z GLOBAL ENSEMBLE SPREAD. THE 12Z CANADIAN APPEARS TOO AMPLIFIED WITH ITS UPPER TROUGH, CONSIDERING THE FLOW PATTERN WHICH FAVORS BROADER TROUGHING ALOFT. TO DEAL WITH RESIDUAL PROGRESSION ISSUES ACROSS THE NORTHERN MID-ATLANTIC STATES, PREFER A COMPROMISE OF THE 12Z GFS/12Z UKMET/12Z ECMWF WITH AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ROTH