MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 241 PM EDT FRI JUN 19 2015 VALID JUN 19/1200 UTC THRU JUN 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION AND FINAL MODEL PREFERENCES NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. ...TROPICAL DEPRESSION BILL... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: AVERAGE THE NAM AND GFS ARE IN GENERAL AGREEMENT WITH THE MODEL CONSENSUS WITH TRACKING BILL EASTWARD ALONG THE OHIO RIVER THROUGH SATURDAY AND INTO THE MID-ATLANTIC STATES SATURDAY NIGHT/SUNDAY MORNING. BY EARLY SUNDAY THE NAM BECOMES A LITTLE FASTER/FARTHER EAST RELATIVE TO CONSENSUS. THE UKMET IS RELATIVELY CLOSE TO CONSENSUS BUT BECOMES A LITTLER TOO FAR NORTH WITH THE SURFACE LOW BY SUNDAY MORNING ACROSS THE MID-ATLANTIC. THE GEM GLOBAL SEEMS TO LOSE THE SURFACE LOW ALTOGETHER BY 18Z SATURDAY AND IS AN OUTLIER. THE GFS/ECMWF ARE PREFERRED AT THIS TIME. FOR THE LATEST DETAILS ON BILL...PLEASE REFER TO THE LATEST WPC ADVISORY. ...LOW PRESSURE SYSTEM MOVING FROM THE ROCKIES INTO THE CENTRAL/NORTHERN PLAINS TODAY... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: ABOVE AVERAGE THE DEVELOPMENT OF THIS AREA OF LOW PRESSURE AT THE SURFACE APPEARS TO BE A RESPONSE TO A FAIRLY SUBTLE SHORTWAVE ALOFT WHICH IS FORECAST TO MOVE ACROSS THE NORTHERN PLAINS TONIGHT. AS WITH ANY SUBTLE FEATURE...THERE ARE SOME DIFFERENCES. THE NAM DEPICTS A SHARPER SHORTWAVE RELATIVE TO OTHER GUIDANCE BY 12Z SATURDAY ACROSS MINNESOTA. THE NAM IS ALSO A BIT FAST WITH THE WAVE RELATIVE TO OTHER GUIDANCE. AT THIS TIME...PREFERENCE IS FOR A BLEND OF THE GFS AND THE ECMWF AS THESE TWO SOLUTIONS APPEAR TO REPRESENT A GOOD CONSENSUS. ...UPPER-LEVEL TROUGH APPROACHING THE PACIFIC NORTHWEST ON SUNDAY... PREFERENCE: ECMWF/12Z GEFS MEAN/00Z ECMWF ENSEMBLE MEAN CONFIDENCE: AVERAGE THE GFS IS APPEARS TO BE A LITTLE TOO QUICK WITH THE EASTWARD PROGRESSION OF THIS TROUGH...DEPICTING A FASTER SOLUTION THAN THE ECMWF...00Z ECMWF ENSEMBLE MEAN AND THE 12Z GEFS MEAN. THE NAM APPEARS TO BE CLOSER TO CONSENSUS INITIALLY BUT BECOMES OVERLY AMPLIFIED BY SUNDAY NIGHT. GIVEN THE SPREAD AND THAT THIS SYSTEM IS STILL OUT OVER THE NORTH PACIFIC...PREFER AN ENSEMBLE CONSENSUS APPROACH AT THIS TIME. THE 12Z GEFS MEAN AND THE 00Z ECMWF ENSEMBLE MEAN ARE IN DECENT AGREEMENT WITH RESPECT TO THE TIMING AND AMPLITUDE OF THIS TROUGH. THE 12Z ECMWF HAS ALSO COME INTO BETTER AGREEMENT WITH THE ENSEMBLE MEANS...AND IS THE PREFERRED DETERMINISTIC SOLUTION AT THIS TIME...ALONG WITH THE GEFS AND 00Z ECMWF ENSEMBLE MEAN. ...UPPER-LEVEL ENERGY MOVING INTO TEXAS FROM MEXICO SATURDAY INTO SUNDAY... PREFERENCE: ECMWF/GEM GLBL BLEND CONFIDENCE: BELOW AVERAGE MODELS ARE IN GENERAL AGREEMENT ON UPPER-LEVEL ENERGY MOVING NORTHWARD FROM MEXICO INTO CENTRAL TEXAS SATURDAY INTO SUNDAY. SOLUTIONS DIFFER ON THE INTENSITY OF THE FEATURE. THE 12Z ECMWF DEPICTION OF THIS FEATURES APPEARS SLIGHTLY WEAKER RELATIVE TO THE 00Z RUN...WHICH FITS IN NICELY WITH THE PREFERENCE EXPRESSED PREVIOUSLY OF A BLEND OF THE 00Z ECMWF/UKMET/CMC. THE NAM AND GFS SHOW A LESS FOCUSED/MORE SPREAD OUT AREA OF UPPER-LEVEL VORTICITY. THE UKMET SHOWS A WEAKER DISTURBANCE THAN ITS 00Z RUN WHILE THE GEM REMAINS CONSISTENT...DEPICTING A SOLUTION SIMILAR TO THE ECMWF. THE COVERAGE OF CONVECTION THAT DEVELOPS SATURDAY AND SUNDAY APPEARS TO GENERALLY VARY PROPORTIONALLY TO THE INTENSITY OF THE UPPER-LEVEL FEATURE DEPICTED BY A GIVEN MODEL. AT THIS TIME...WILL RECOMMEND A BLEND OF THE ECMWF AND GEM GLOBAL. ...SURFACE LOW PRESSURE CROSSING THE NORTHERN PLAINS/MIDWEST SUNDAY NIGHT/MONDAY... ...SURFACE LOW DEVELOPING OVER THE CENTRAL PLAINS ON MONDAY... PREFERENCE: GFS/00Z ECMWF/00Z ECMWF ENSEMBLE MEAN BLEND CONFIDENCE: AVERAGE THE GFS AND ECMWF SHOW SHOW SOME DIFFERENCES WITH RESPECT TO TIMING AND INTENSITY OF THESE FEATURES. THE ECMWF DEPICTS A SOLUTION THAT LIES SOMEWHAT ON THE SLOW SIDE OF THE SPREAD WITH RESPECT TO THE UPPER-LEVEL WAVE SKIRTING THE NORTHERN PLAINS SUNDAY NIGHT/EARLY MONDAY. THE GEM GLOBAL IS A SLOW OUTLIER AND IS BEING DISCARDED. THE NAM IS ON THE FAST SIDE OF THE SPREAD. THE GFS AND UKMET BOTH APPEAR TO LIE IN THE MIDDLE OF THE SPREAD AT THIS TIME. A SOLUTION SOMEWHERE BETWEEN THE GFS AND THE 00Z ECMWF/00Z ECMWF ENSEMBLE MEAN APPEARS TO BE REASONABLE AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN