MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1225 PM EDT TUE MAY 19 2015 VALID MAY 19/1200 UTC THRU MAY 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...FRONTAL WAVE TRACKING FROM THE PLAINS TO THE ATLANTIC COAST... PREFERENCE: BLEND OF 12Z NAM/00Z CANADIAN...SUPPORTED BY 00Z ECMWF ENSEMBLE MEAN A SHORTWAVE TROUGH EJECTING FROM THE SOUTHERN ROCKIES WILL BE ABSORBED INTO A LARGER SCALE TROUGH OVER THE NORTHEAST U.S. THE SHORTWAVE IS THE INITIAL DRIVER BEHIND A FRONTAL WAVE WHICH MAY DEEPEN AS IT REACHES THE ATLANTIC COAST AND TURNS NORTHWARD OFFSHORE. THE NAM AND ECMWF ENSEMBLE MEAN HAVE BEEN CONSISTENT FROM RUN TO RUN. AS NOTED IN OUR PREVIOUS DISCUSSION...THE 00Z OPERATIONAL ECMWF DEVIATED NORTH OF THE ENSEMBLE CONSENSUS WITH RESPECT TO THE SURFACE FORECAST OFFSHORE. IT WAS ALSO SOMEWHAT DEEP IN THE MID LEVELS. MEANWHILE...THE GFS FITS CONSENSUS IN THE MID LEVELS...BUT CONTINUED TO SHOW A MUCH WEAKER SURFACE REFLECTION WITH THIS SYSTEM. THE 12Z RUN DID MOVE A LITTLE MORE TOWARD OUR PREFERENCE...BUT THE 12Z NAM AND 00Z CANADIAN BETTER FIT A CONSENSUS / ECMWF-ENSEMBLE-LED SOLUTION. ...DEEP TROUGH OVER THE WESTERN U.S... PREFERENCE: BLEND OF 12Z NAM/GFS WITH 00Z UKMET THE ECMWF ENSEMBLE MEAN HAD LED THE WAY IN CONSISTENTLY FORECASTING THE DEPTH OF THE WESTERN U.S. TROUGH...BUT THE GEFS MEAN HAD DEEPENED THROUGH SUCCESSIVE RUNS...AND BY 06Z PRODUCED A DEPTH SIMILAR TO THAT OF THE ECMWF MEAN. THE MAJORITY OF OPERATIONAL MODELS ARE PRODUCING A CLOSED CIRCULATION NEAR LAS VEGAS BY 23/00Z...WITH CONSENSUS BEING A BIT SLOWER AND MORE CLOSED THAN THE ECMWF AND ECMWF ENSEMBLE MEAN. THE OPERATIONAL ECMWF DOES SEEM TO BODILY SHIFT THE TROUGH EASTWARD AT THE INFLUENCE OF A RELATIVELY SMALL SHORTWAVE ROUNDING THE BASE ON DAY 3. THE NON-ECMWF SOLUTIONS APPEAR MORE REALISTIC IN HANDLING THIS SHORTWAVE...AND GIVEN THEIR AGREEMENT...WE MOVED OUR PREFERENCE TOWARD THE NAM/GFS/UKMET. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE