MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1127 PM EST WED JAN 14 2015 VALID JAN 15/0000 UTC THRU JAN 18/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...SHORTWAVE CURRENTLY OVER THE SOUTHWEST...REACHING THE SOUTHEAST LATE THURSDAY... PREFERENCE: NON-GEM CONSENSUS CONFIDENCE: ABOVE AVERAGE THE 12Z GEM IS SEEN AS BEING A RELATIVELY WEAK OUTLIER WITH THIS ENERGY AS IT TRAVERSES THE SOUTHERN TIER STATES. THE REMAINING MODELS ARE NOW RATHER WELL CLUSTERED...SO A NON-GEM CONSENSUS WILL BE PREFERRED. ...DEEP UPPER TROUGH AND RELATED COLD FRONT IMPACTING NEW ENGLAND FRIDAY... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS HAVE TRENDED TOWARD ONE ANOTHER WITH THE DETAILS OF THE DEEP TROUGH THAT WILL IMPACT NEW ENGLAND ON FRIDAY...AND ARE IN GOOD AGREEMENT ON THE LARGE SCALE. WILL PREFER A GENERAL MODEL COMPROMISE TO RESOLVE ANY MINOR TIMING/AMPLITUDE DIFFERENCES. ...COMPACT SHORTWAVE CROSSING THE NORTHWEST THROUGH THURSDAY... PREFERENCE: NON-GEM CONSENSUS CONFIDENCE: AVERAGE THE MODELS TAKE THE COMPACT SHORTWAVE CURRENTLY APPROACHING THE PACIFIC NORTHWEST AND WEAKEN IT ON THURSDAY AS IT ADVANCES ACROSS THE INTERIOR WHILE ENCOUNTERING A RIDGE AXIS ALOFT. A DAMPENED VERSION OF THE SHORTWAVE WILL ADVANCE DOWNSTREAM INTO THE HIGH PLAINS ON FRIDAY. THE 12Z GEM BECOMES THE WEAKEST AND FASTEST SOLUTION WITH THIS SYSTEM. THE REMAINING MODELS TEND TO AGREE WELL NOW WITH DEPTH AND TIMING. A NON-GEM CONSENSUS WILL BE PREFERRED TO RESOLVE ANY MINOR TIMING DIFFERENCES/AMPLITUDE DIFFERENCES. ...SHORTWAVE CROSSING THE NORTHWEST AND DIGGING INTO THE PLAINS AND MS/OH VALLEYS... ...COLD FRONT CROSSING OUT INTO THE PLAINS AND MS VALLEY THROUGH SATURDAY... PREFERENCE: BLEND OF THE 12Z ECMWF AND 12Z GEM CONFIDENCE: BELOW AVERAGE THERE IS GENERALLY GOOD MODEL AGREEMENT WITH AN APPROACHING SHORTWAVE AND CORRESPONDING COLD FRONT INTO THE PACIFIC NORTHWEST THURSDAY NIGHT. HOWEVER...DIFFERENCES GROW DOWNSTREAM ACROSS THE PLAINS AND MS/OH VALLEY SATURDAY THROUGH SUNDAY WITH THE DETAILS OF A LARGER SCALE TROUGH AMPLIFICATION. THE 00Z NAM AND 00Z GFS ARE BOTH GENERALLY WEAKER THAN THE GLOBAL MODEL CONSENSUS WITH THE DEPTH OF THE TROUGH ONCE IT REACHES THE CENTRAL U.S....AND THE 00Z GFS ALSO BECOMES THE SLOWEST MODEL WITH THE HEIGHT FALLS. CONVERSELY...THE 12Z ECMWF AND ESP THE 12Z UKMET ARE STRONGER AND A BIT FASTER TO ADVANCE HEIGHT FALLS EAST OF THE MS VALLEY BY SUNDAY...AND IN THE CASE OF THE UKMET THERE IS SUGGESTION OF THE TROUGH GOING NEGATIVE TILT OVER THE OH/TN VALLEYS BY EARLY SUNDAY. THE 12Z GEM SPLITS THE DIFFERENCE BETWEEN THE WEAKER AND STRONGER CAMPS. THE 18Z GEFS MEAN AND 00Z ECENS MEAN STRONGLY SUGGEST THAT THE NAM AND GFS ARE TOO SLOW...AND ARE MORE CLOSELY ALIGNED WITH THE ECMWF AND UKMET. REGARDING DEPTH...NO MODEL OR ENSEMBLE MEAN FAVORS THE INTENSITY OF THE UKMET. THE 12Z GEM GENERALLY HAS THE BEST SUPPORT FROM THE GEFS MEAN AND ECENS MEAN...HOWEVER THERE HAS BEEN A BROADER TREND IN THE MODELS TO HAVE A MORE AMPLIFIED TROUGH MOVING TOWARD THE OH VALLEY BY SUNDAY. THEREFORE...ACCOUNTING FOR CLUSTERING AND TRENDS...A BLEND OF THE 12Z GEM AND 12Z ECMWF WILL BE PREFERRED. ...WEAK IMPULSE AND COLD FRONT REACHING THE PACIFIC NORTHWEST ON SAT... ...SHORTWAVE AND ATTENDANT COLD FRONT REACHING THE PACIFIC NORTHWEST ON SUNDAY... PREFERENCE: 12Z ECMWF CONFIDENCE: AVERAGE THE MODELS SHOW ADDITIONAL UPSTREAM PACIFIC ENERGY ARRIVING ACROSS THE PACIFIC NORTHWEST SATURDAY AND SUNDAY...WITH THE SHORTWAVE TROUGH ON SUNDAY THE STRONGEST FEATURE OF NOTE. THERE IS NOT MUCH MASS FIELD SPREAD ALOFT WITH THE ENERGY ON SATURDAY WHICH WILL DRIVE A WEAK COLD FRONT PROGRESSIVELY INTO THE NORTHWEST BEFORE WEAKENING. STRONG ONSHORE FLOW AND A SECOND COLD FRONT WILL ARRIVE ON SUNDAY. THE 00Z NAM AND 00Z GFS BOTH APPEAR A BIT TOO STRONG ALOFT WITH THE DETAILS OF THE SHORTWAVE ON SUNDAY THAT APPROACHES THE REGION...AND THE 00Z NAM ALSO APPEARS TOO FAR SOUTH WITH AN ATTENDANT SURFACE LOW. THE 12Z ECMWF/12Z UKMET AND 12Z GEM SOLUTIONS ALL CLUSTER TOGETHER BETTER WITH THE SHORTWAVE AND ATTENDANT SURFACE LOW/FRONTAL DETAILS. A NON-NCEP CONSENSUS LED BY THE 12Z ECMWF WILL BE FAVORED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON