MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 204 PM EST SUN DEC 14 2014 VALID DEC 14/1200 UTC THRU DEC 18/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION AND FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. CYCLONE AFFECTING THE PLAINS AND MIDWEST... EVENTUAL COASTAL LOW DEVELOPMENT OFF NEW ENGLAND ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 12Z NAM BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS SHOW VERY GOOD AGREEMENT THROUGH MONDAY...HAVING CONVERGED UPON A COMMON SOLUTION SINCE YESTERDAY. SOME MINOR PLACEMENT DIFFERENCES APPEAR FOR TUE INTO WED WITH ONLY THE 12Z NAM STANDING OUT AS DIFFERENT REGARDING THE TRACK OF THE PRIMARY LOW INTO THE NORTHEAST AND SECONDARY LOW DEVELOPMENT OFF OF THE NEW ENGLAND COAST. GIVEN THE GOOD AGREEMENT OUTSIDE OF THE NAM AND WITH A NON NAM CONSENSUS BEST MATCHING THE LATEST TRENDS IN THE ENSEMBLE GUIDANCE...A NON NAM BLEND IS PREFERRED. NORTHERN STREAM TROUGH DIPPING TOWARD THE UPPER MIDWEST/GREAT LAKES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE CONCERNING THE 540 DM LINE AT 500 MB...ENSEMBLE SPREAD HAS DIMINISHED SINCE YESTERDAY...BUT ENSEMBLE MODEL CLUSTERS REMAIN WITH GEFS MEMBERS WEST OF ECMWF MEMBERS AT 00Z/17 ACROSS THE N-CNTRL U.S. WHILE CMC MEMBERS ARE NEAR OR NORTHEAST OF THE ECMWF MEMBERS. BY 00Z/18...THE AGREEABLE 00Z ECMWF/UKMET HAD MARKEDLY TRENDED TOWARD THE GFS BUT TODAYS 12Z ECMWF/UKMET HAVE MADE ONLY MINOR NWD SHIFTS. 850 MB LOW PLACEMENT BY TUE AND WED SHOWS DECENT AGREEMENT BETWEEN THE GEFS AND EC MEANS SUPPORTED BY THE 12Z GFS/ECMWF/UKMET. GIVEN BETTER SURFACE LOW SUPPORT FROM THE ENSEMBLES...THE GFS/ECMWF/UKMET WILL BE PREFERRED. CALIFORNIA AND WESTERN SHORTWAVES MAKING LANDFALL MON AND TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM...12Z ECMWF BLEND CONFIDENCE: BELOW AVERAGE RUN TO RUN CONTINUITY WITH INDIVIDUAL SHORTWAVES REMAINS POOR FROM THE DETERMINISTIC GUIDANCE BUT ENSEMBLE MEANS SHOW PRETTY GOOD AGREEMENT THROUGH F084 HOURS. THE FLOW IN THE PACIFIC REMAINS VOLATILE WITH SMALL ADJUSTMENTS UPSTREAM RESULTING IN LARGE DIFFERENCES DOWNSTREAM ACROSS THE WESTERN CONUS. THE TWO MODELS THAT SHOW REASONABLE AGREEMENT ACROSS CALIFORNIA ARE THE 12Z NAM AND 12Z ECMWF WHICH JUST HAPPEN TO SHOW RESEMBLANCE TO THE SREF/GEFS/EC MEANS AT 500 MB...WHICH TRANSLATES INTO THE LOWER LEVELS AS WELL. PACIFIC NORTHWEST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM...12Z ECMWF BLEND CONFIDENCE: BELOW AVERAGE OVERALL DETERMINISTIC/ENSEMBLE MODEL GUIDANCE HAS SHOWN LESS AMPLIFICATION WITH AN UPPER TROUGH AMPLIFYING WEST OF BRITISH COLUMBIA BY MON EVENING COMPARED TO PRIOR RUNS. RUN TO RUN CONTINUITY IS LESS THAN AVERAGE...ALTHOUGH PERHAPS A BIT BETTER THAN FARTHER DOWN THE WEST COAST. AN ADDITIONAL SHORTWAVE TROUGH AXIS IS FORECAST TO REACH THE PACIFIC NORTHWEST COAST BY LATE WED WITH THE LATEST DETERMINISTIC GUIDANCE SHOWING A NUMBER OF POSSIBILITIES. AGAIN...SIMILAR TO ABOVE...THE NAM/ECMWF SHOW BETTER AGREEMENT TO EACH OTHER AND THE LATEST ENSEMBLE MEANS THAN THE 12Z GFS OR THE UKMET/CMC. THE 12Z ECMWF IS SHOWING A BIT MORE SEPARATION BETWEEN TWO SHORTWAVE TROUGH AXES OVER THE SOUTHWEST WED EVENING...EMBEDDED WITHIN A BROADER LARGE SCALE UPPER TROUGH...BUT STILL MATCHES BETTER TOWARD THE ENSEMBLE MEANS AND 12Z NAM THAN THE REMAINING GUIDANCE. INDIVIDUAL SHORTWAVE ORIENTATION/TIMING IS DIFFICULT TO PIN DOWN WITH THE BEST APPROACH GOING TOWARD THE ENSEMBLES AND THEIR MEANS AT THIS POINT IN TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO