MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1151 AM EST MON NOV 17 2014 VALID NOV 17/1200 UTC THRU NOV 21/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ===================================================== 12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ===================================================== THE NAM INITIALIZED 500 MB HEIGHTS GENERALLY 8 TO 19 METERS TOO COLD OVER MUCH OF THE U.S. IT IS UNCERTAIN TO WHAT DEGREE THIS AFFECTED ITS FORECAST OUTPUT WHICH LOOKED REASONABLE ON THE WHOLE. GFS INITIALIZATION ERRORS DID NOT APPEAR TO SIGNIFICANTLY AFFECT ITS LARGE SCALE OUTPUT. ===================================================== ...TROUGH IMPACTING THE PACIFIC NORTHWEST WED/THU... PREFERENCE: 12Z GFS A SHORT WAVELENGTH BUT POTENTIALLY DEEP TROUGH IS FORECAST TO PINCH OFF OF THE LARGER SCALE TROUGH IN THE ALEUTIANS AND RACE TOWARD THE WEST COAST...FOLLOWING THE SOUTHERN CHANNEL OF A FLOW REGIME THAT IS SPLITTING OVER WESTERN CANADA. THIS SCENARIO COULD YIELD A FAST MOVING BUT POTENT WEATHER SYSTEM. AS WOULD BE EXPECTED...THE MODELS SHOW A MODERATE AMOUNT OF TIMING AND STRENGTH DIFFERENCES. BUT ALL OF THE OPERATIONAL MODELS BRING THE SYSTEM ONSHORE SOMETIME THURSDAY. THE NAM IS ON THE FAST SIDE. THE ECMWF MAY BE A LITTLE SLOW. THE 12Z GFS REPRESENTS A NICE AVERAGE OF THE ENSEMBLE MEANS...AND THE GFS TRENDED JUST SLIGHTLY DEEPER THAN ITS 00Z RUN. THE OTHER MODELS ARE CERTAINLY NOT OUTLIERS...AND COULD BE INCORPORATED IN THE FORECAST...BUT THE GFS APPEARS TO BEST REPRESENT CONSENSUS. OTHER MODELS MAY BE ADDED TO OUR PREFERENCE WHEN WE SEE THE REST OF THE 12Z CYCLE. ...TROUGH MOVING INTO THE SOUTHWEST WEDNESDAY... PREFERENCE: BLEND OF 12Z NAM/GFS WITH 00Z ECMWF A CLOSED LOW AROUND 140 DEGREES WEST WILL BE KICKED TOWARD THE SOUTHWEST U.S...REACHING CALIFORNIA EARLY WEDNESDAY. A MATURE SYSTEM BEING REABSORBED IN THE WESTERLIES SHOULD OPEN UP...CONTRARY TO THE 00Z UKMET AND CANADIAN SOLUTIONS. THERE IS MORE ENSEMBLE SUPPORT FOR THE NAM/GFS/ECMWF. THESE MODELS VARY IN AMPLITUDE BY DAY 3 AS THE MID LEVEL WAVE REACHES THE SOUTHERN HIGH PLAINS. DIFFERENCES ARE MINIMAL IN THE LOWER LEVELS...HOWEVER...FROM THE SURFACE UP TO 700 MB. THEREFORE...WE RECOMMEND A BLEND. ...SHORTWAVES MOVING THROUGH THE GREAT LAKES REGION TUE/WED... PREFERENCE: ANY OF 12Z NAM...09Z SREF...00Z ECMWF THE MODELS ARE STRUGGLING AS TO THE DETAILS OF THE MID LEVEL SHORTWAVES NEAR THE CORE OF A COLD SYNOPTIC SCALE TROUGH IN SOUTHEAST CANADA AND THE GREAT LAKES. ENSEMBLE TRENDS SUPPORT THE NOTION OF THE TROUGH ASSUMING A NEUTRAL OR SLIGHTLY NEGATIVE TILT AS A PRONOUNCED SHORTWAVE DIVES TOWARD THE WESTERN LAKES ON DAY 2...WEDNESDAY. THE 00Z UKMET WAS OUT AHEAD OF CONSENSUS FOR TIMING AND WAS DEEPER/COLDER. THE CANADIAN WAS THE SLOWEST. THE ECMWF...ALTHOUGH IT HAS NOT HAD THE BEST RUN TO RUN CONTINUITY...CLUSTERED REASONABLY WELL WITH THE 12Z NAM/GFS...ALL WAFFLING AROUND THE ENSEMBLE MEANS. FORTUNATELY...THE LAKE EFFECT PRECIPITATION FORECAST IS LESS DEPENDENT ON THESE SHORTWAVE DETAILS. GIVEN GOOD AGREEMENT IN THE LOW LEVELS...THE HIGHER RESOLUTION MODELS FEATURING HEAVIER PRECIPITATION ARE PREFERRED. ...UPPER LEVEL TROUGH SWINGING ACROSS THE EAST COAST... PREFERENCE: ANY OF THE OPERATIONAL MODELS THIS SYSTEM IS RELEVANT THROUGH WEDNESDAY MORNING...BY WHICH TIME COLDER AND DRIER CONDITIONS WILL BE ENTRENCHED ACROSS THE EAST COAST STATES. MODELS SHOWS STRONG AGREEMENT THROUGH THAT TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE