MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1147 AM EST SUN NOV 30 2014 VALID NOV 30/1200 UTC THRU DEC 04/0000 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. ================================================== ...DEEP TROUGH APPROACHING CALIFORNIA... PREFERENCE: BLEND OF 12Z NAM/GFS WITH 06Z GEFS MEAN THE 00Z ECMWF APPEARED TOO FAST IN OPENING AND DE-AMPLIFYING THE DEEP LOW OFF THE WEST COAST. WHILE DIFFERING IN THE DEGREE OF POSITIVELY TILTED TROUGHING THAT IS LEFT BEHIND AFTER THIS SYSTEM COMES ONSHORE...THE VARIOUS ENSEMBLES...GEFS...ECMWF...AND CANADIAN...PREDICT SIMILAR TIMING FOR THE PRIMARY UPPER LOW TO REACH THE COAST AS AN OPEN TROUGH AXIS...ROUGHLY 04/00Z. RECENT NAM AND GFS RUNS FIT WELL WITH THE MEANS. THE MODELS VARY MORE GREATLY...HOWEVER...IN HANDLING THE SURFACE AND NEAR SURFACE FLOW...ESPECIALLY JUST OFFSHORE. WE RECOMMEND BLENDING IN THE 06Z GEFS MEAN WHICH AVOIDS THE TIGHTLY WOUND SURFACE LOW SEEN IN THE NAM ON DAY 3 AND THE ODD APPEARANCE OF A LOW CENTER WEST OF THE MID LEVEL TROUGH IN THE GFS ON DAY 3. ...EASTERN U.S FRONTAL ZONE AND ASSOCIATED PRECIPITATION... PREFERENCE: BLEND OF THE OPERATIONAL MODELS...LESS WEIGHT ON THE GFS A LOW AMPLITUDE SOUTHERN STREAM WAVE WAS ENTERING THE WESTERN U.S. TODAY. THIS WILL MOVE RAPIDLY EAST...CONTRIBUTING TO PRECIPITATION ALONG A SINKING FRONTAL ZONE FROM THE MID MISSISSIPPI VALLEY TO THE SOUTHERN APPALACHIANS AND MID ATLANTIC. THE MODELS HANDLE THIS FEATURE SIMILARLY...AND THEIR PRECIPITATION AXES ARE WELL ALIGNED. THE MOST NOTEWORTHY MODEL DIFFERENCE APPEARS TO BE THE WARMER GFS THERMAL FIELDS WITHIN THE COLD AIR DAMMING REGIME EAST OF THE SPINE OF THE APPALACHIANS ON DAYS 2/3. THE GFS WAS ALSO SLIGHTLY LESS PRONOUNCED IN THE 500 MB HEIGHT/VORTICITY FIELDS. WITH THE OTHER MODELS IN BETTER AGREEMENT...WE RECOMMEND LESS WEIGHT ON THE GFS SOLUTION. ...NORTHERN STREAM TROUGH SWINGING FROM THE PAC NW TO GREAT LAKES... PREFERENCE: BLEND OF 12Z NAM/GFS MODEL SPREAD IS NOT TOO LARGE FOR THIS BROAD AND LOW AMPLITUDE SYSTEM WHICH IS MOISTURE STARVED UNTIL NEARING THE GREAT LAKES AND NEW ENGLAND. THE NAM AND GFS BOTH TRENDED A LITTLE FASTER. ALTHOUGH THE 00Z UKMET AND CANADIAN WERE THOUGHT TO BE TOO FAST...THE CONSENSUS IS SHIFTING AWAY FROM THE SLOWER 00Z ECMWF. ENSEMBLE SURFACE LOW PLOTS SHOW A CONVERGENCE OF SOLUTIONS TOWARD THE 04/00Z POSITION SEEN IN RECENT GFS RUNS...CENTRAL QUEBEC. THE 12Z NAM AND GFS ARE SIMILAR ALONG THE SOUTHERN EXTENSION OF THE ATTENDANT COLD FRONT...STRETCHING FROM SOUTHWEST TEXAS TO CENTRAL TENNESSEE AT 04/00Z. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE