MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 114 AM EDT TUE JUL 21 2015 VALID JUL 21/0000 UTC THRU JUL 24/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO IMPACT THEIR SHORT RANGE FORECASTS. 700-500 MB TROUGH MOVING INTO THE GREAT BASIN WHILE WEAKENING THROUGH ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE NO SIGNIFICANT DIFFERENCES WERE NOTED WITH THIS SYSTEM. COLD FRONT MOVING INTO THE NRN PLAINS BY THE END OF THE WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THERE ARE SOME DIFFERENCES WITH THE STRENGTH/TIMING OF THE RELATED UPPER TROUGH MOVING INTO SWRN CANADA WHICH IMPACT THE TIMING OF A SURFACE LOW IN SRN CANADA. HOWEVER...THE DIFFERENCES WITH THE TIMING OF THE COLD FRONT INTO THE NRN PLAINS SEEM TO BE MINIMAL. GIVEN THE TIME FRAME IN QUESTION...F060-F084 HOURS...CONFIDENCE IS ONLY AVERAGE WITH POSSIBLE CHANGES OCCURRING WITH SUBSEQUENT MODEL RUNS. UPPER LEVEL TROUGH ALONG THE WEST COAST TUE-FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS...12Z ECMWF...12Z CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE SOME PLACEMENT DIFFERENCES WITH THE UPPER TROUGH AXIS NEAR THE WEST COAST FRI MORNING...WITH THE GFS/CMC SHOWING GOOD AGREEMENT WHILE THE 12Z ECMWF IS HELD BACK TO THE WEST A BIT. HOWEVER...THE NAM IS WEAKER HERE AND THE 12Z UKMET IS MUCH FARTHER WEST. THE LATEST ENSEMBLE SPREAD SHOWS A WIDE RANGE OF SOLUTIONS...BUT THE GFS/ECMWF/CMC ARE WITHIN THE MIDDLE OF THE LATEST SPREAD WHILE THE UKMET IS TOWARD THE EDGE. UPPER LEVEL TROUGH MOVING ACROSS THE NORTHEAST WITH COLD FRONT MOVING ACROSS THE EAST COAST TODAY POSSIBLE SURFACE LOW ALONG FRONT IN THE SOUTHEAST BY THU/FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/12Z ECMWF BLEND CONFIDENCE: ABOVE AVERAGE THE TIMING OF THE COLD FRONT IS AGREEABLE IN THE LATEST MODEL GUIDANCE...BUT SOME DIFFERENCES SHOW UP WITH A SURFACE LOW FORECAST TO DEVELOP IN THE SOUTHEAST BY THE END OF THE WEEK. THE 12Z UKMET/CMC ARE EAST OF THE WELL CLUSTERED ENSEMBLES BY THU...BUT FALL INTO BETTER AGREEMENT BY FRI. THE NAM ENDS UP WEAKER AND MORE DISORGANIZED COMPARED TO THE REMAINING MODELS BY FRI. GIVEN SOME OF THESE DIFFERENCES...THE GFS/ECMWF ARE MOST IN LINE THROUGHOUT THE SHORT RANGE PERIOD. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO