MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 125 PM EST FRI DEC 04 2015 VALID DEC 04/1200 UTC THRU DEC 08/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION INCLUDING THE UKMET/CANADIAN/ECMWF AND PREFERENCES SHORTWAVE TROUGH OVER THE CENTRAL GULF COAST... MODELS SHOW GOOD LARGE-SCALE AGREEMENT. REFER TO THE QPFPFD FOR MORE INFORMATION ON DIFFERENCES WITH QPF. UPPER TROUGH INFLUENCING THE WEST COAST SUNDAY... PREFERENCE: EQUAL BLEND NAM/ECMWF CONFIDENCE: AVERAGE THE NAM HAS TRENDED TOWARD GREATER AMPLIFICATION WITH THE LEADING EDGE OF THE TROUGH REACHING THE OR/N. CA COAST BY 12Z SUN...WHICH IS CLOSE TO THE ECMWF. MEANWHILE...THE NAM HAS ALSO BECOME MORE AMPLIFIED WITH THE LEADING EDGE OF THE NORTHERN STREAM TROUGH REACHING THE WA COAST SUNDAY NIGHT...WITH THE GFS CONSIDERABLY FASTER THAN ITS PREVIOUS AND CLOSE TO THE FAST EDGE OF THE GUIDANCE. GIVEN CLOSER AGREEMENT BETWEEN THE NAM/ECMWF...RECOMMEND A BLEND OF THE NAM/ECMWF...WITH ONLY AVERAGE CONFIDENCE DUE TO THE ENSEMBLE SPREAD AND CONTINUED RUN-TO-RUN VARIABILITY IN MANY SOLUTIONS. CLOSED LOW POSSIBLY INFLUENCING THE OH-TN VALLEYS/APPALACHIANS SUN-MON... PREFERENCE: NAM OR ECMWF CONFIDENCE: BELOW AVERAGE THE NAM HAS HELD STEADY SINCE 06Z AND AGREES WITH THE UKMET/CANADIAN/ECMWF...WHILE THE GFS HAS TRENDED FASTER BUT IS STILL SLOWER ENTERING THE OH/TN VALLEYS. GIVEN ADDITIONAL SUPPORT FROM THE ENSEMBLE MEANS FOR THE FASTER CAMP OF SOLUTIONS...THEIR SOLUTIONS ARE RECOMMENDED...ALTHOUGH WITH BELOW AVERAGE CONFIDENCE GIVEN THE HIGH ENSEMBLE MEMBER SPREAD ACCOMPANYING THE SMALL SIZE AND YET VIGOROUS NATURE OF THIS SYSTEM. LOW PRESSURE POSSIBLY AFFECTING S. FLORIDA MONDAY... PREFERENCE: GFS OR ECMWF CONFIDENCE: AVERAGE THE NAM IS NEARLY AN OUTLIER WITH FASTER AND STRONGER APPROACH OF A SHORTWAVE TROUGH FROM THE YUCATAN PENINSULA RESULTING IN LOW PRESSURE FORMING ALONG THE RESIDUAL FRONTAL BOUNDARY AND AFFECTING S. FLORIDA. THE MAJORITY OF OTHER GUIDANCE IS EITHER WEAKER AND/OR FOCUSES THE LOW TOWARD THE BAHAMAS. THUS...GIVEN STRONGER SUPPORT FOR THE WEAKER AND MORE EASTWARD SCENARIO...RECOMMEND EITHER THE GFS OR ECMWF...WITH AVERAGE CONFIDENCE GIVEN LIMITED SAMPLING FROM THE LOWER LATITUDE AND REDUCED CONFIDENCE OVER THE GULF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES