MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1227 AM EDT MON APR 13 2015 VALID APR 13/0000 UTC THRU APR 16/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM AND GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES ...COLD FRONT EXTENDING FROM THE UPPER MIDWEST INTO THE S. ROCKIES... ...LOW PRESSURE FORMING NEAR THE MID-ATLANTIC COAST WEDNESDAY... PREFERENCE: ECMWF CONFIDENCE: AVERAGE MODELS SHOW SIMILAR TIMING AND STRENGTH WITH THE NORTHERN PORTIONS OF THE FRONTAL SYSTEM INCLUDING THROUGH THE GREAT LAKES/OH VALLEY/NORTHEAST. HOWEVER...ACROSS SOUTHERN PORTIONS OF THE FRONTAL SYSTEM...THE NAM AND 12Z CANADIAN...AND TO SOME EXTENT THE GFS...ARE FARTHER NORTH COMPARED WITH THE REST OF THE GUIDANCE...AND GIVEN THEIR SOUTHERLY AND WEAKENING TRENDS OVER THE LAST FEW CYCLES...THE MORE SOUTHWARD AND SUPPRESSED SOLUTIONS HAVE STRONGER SUPPORT AT THIS TIME...WHICH IS BEST APPROXIMATED BY TO THE ECMWF. ...UPPER LOW NEAR NEW MEXICO... PREFERENCE: MODEL COMPROMISE CONFIDENCE: AVERAGE MODELS SHOW SUBTLE DIFFERENCES WITH ITS WEAKENING AS IT BECOMES ABSORBED IN THE INCREASING SOUTHWESTERLY FLOW AHEAD OF THE NEXT UPPER TROUGH ENTERING THE WEST...BUT OTHERWISE ARE QUITE CLOSE. RECOMMEND A CONSENSUS APPROACH TO RESOLVE THESE SMALL DIFFERENCES. ...SPLITTING SHORTWAVE TROUGH ENTERING THE WEST TUESDAY/WEDNESDAY... PREFERENCE: NAM OR ECMWF CONFIDENCE: AVERAGE THE GFS IS SLOWEST TO SPLIT AND FORM A CLOSED LOW THAT EVENTUALLY DRIFTS ACROSS THE GREAT BASIN. RECENT TRENDS HAVE BEEN FOR EARLIER AND MORE SOUTHWESTWARD SPLITTING. THUS...THE GFS APPEARS TO BE SLOW TO LATCH ON. OTHERWISE...THE NAM AND ECMWF SHOW GOOD OVERALL AGREEMENT THROUGH THE PERIOD AND HAVE GOOD SUPPORT FROM THE ENSEMBLE MEANS...ALTHOUGH THE SREF MEAN IS A BIT TO THE SOUTH OF THE CONSENSUS AND THUS IS LESS RECOMMENDED THAN THE OTHERS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml...