MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 101 PM EDT MON OCT 27 2014 VALID OCT 27/1200 UTC THRU OCT 31/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...CLOSED LOW LIFTING AWAY FROM UPPER NEW ENGLAND... PRELIMINARY PREFERENCE: GENERAL MODEL CONSENSUS FORECAST CONFIDENCE: HIGH A PROGRESSIVE MID-LATITUDE PATTERN WILL HELP LIFT A CLOSED LOW CURRENTLY SPINNING NORTH OF NOVA SCOTIA. THIS WILL EVENTUALLY CARRY THE SYSTEM WELL OFF THE MAP AND NOT BE OF CONSEQUENCE TO THE STATES. A GENERAL MODEL CONSENSUS IS SUPPORTED HERE. ...AXIS OF HEIGHT FALLS TRACKING THROUGH THE MIDDLE OF THE COUNTRY... ...PROGRESSIVE COLD FRONT... PRELIMINARY PREFERENCE: BLEND OF THE 00Z ECMWF/UKMET WITH THE 12Z GFS FORECAST CONFIDENCE: AVERAGE AN AREA OF HEIGHT FALLS MIGRATING EASTWARD WILL CARRY A WELL-DEFINED FRONTAL ZONE THROUGH THE CENTER OF THE COUNTRY AND EVENTUALLY TO THE EASTERN SEABOARD BY LATE WEDNESDAY. AT TIMES THE 00Z CMC SEEMED A BIT SLOW WITH THE PLACEMENT OF THE COLD FRONT. LOOKING ALOFT...THE MODELS ARE IN GENERAL AGREEMENT WITH THE LEAD UPPER LOW LIFTING NORTHEASTWARD TOWARD UPPER NEW ENGLAND. HOWEVER...THERE ARE MORE DIFFERENCES UPSTREAM AS A SHORTWAVE PROPAGATES THROUGH THE MID-ATLANTIC BY EARLY THURSDAY. THE 00Z ECMWF/UKMET SHOWS A BIT MORE AMPLIFICATION RELATIVE TO THE FLATTER 12Z GFS. FOR NOW WILL SPLIT BETWEEN THE TWO CAMPS AS THE SENSIBLE WEATHER IMPACTS ARE MINIMAL WITH THIS ASPECT OF THE SYSTEM. ...SYSTEM FLATTENING OUT ACROSS THE PACIFIC NORTHWEST ON TUESDAY... PRELIMINARY PREFERENCE: A NON-12Z NAM MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE ENERGY MOVING TOWARD THE PACIFIC NORTHWEST WILL GRADUALLY WEAKEN AS IT MOVES INLAND AS THE FLOW FLATTENS ACROSS THE WESTERN PORTION OF THE CONUS. WHAT REMAINS OF THIS FEATURE WILL BECOME EMBEDDED IN NORTHWESTERLY FLOW ALOFT AND MOVE THROUGH THE MIDDLE MS VALLEY BY EARLY THURSDAY. THE 12Z NAM APPEARS SLOW WITH THE EVOLUTION OF THIS SYSTEM. AGREEMENT DOWNSTREAM APPEARS REASONABLE ENOUGH TO FAVOR A NON-12Z NAM SOLUTION. ...UPPER TROF DIGGING TOWARD THE UPPER MIDWEST BY 31/0000Z... PRELIMINARY PREFERENCE: A NON-00Z CMC MODEL COMPROMISE FORECAST CONFIDENCE: AVERAGE AS A HIGH-AMPLITUDE PATTERN BECOMES REESTABLISHED ACROSS THE U.S...A PROGRESSIVE SHORTWAVE IS EXPECTED TO APPROACH THE UPPER MIDWEST BY 31/0000Z. THE SPAGHETTI PLOTS DO NOT SHOW A WHOLE LOT OF UNCERTAINTY WITH A MAJORITY OF THE DETERMINISTIC GUIDANCE RESIDING WITHIN THE NOTED SPREAD. IT DOES SEEM THE 00Z CMC IS THE MOST OUTLYING SOLUTION FAVORING AN UPPER TROF POSITION WELL NORTH OF THE U.S./CANADIAN BORDER. FOR NOW WILL LEAN ON A NON-00Z CMC MODEL COMPROMISE WHILE AWAITING ADDITIONAL 12Z GUIDANCE. ...STRONG TROF NEARING THE PACIFIC NORTHWEST BY LATE THURSDAY... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE WITH A RIDGE BUILDING ACROSS THE ROCKY MOUNTAIN CHAIN...ANOTHER STRONG UPPER TROF WILL APPROACH THE WEST COAST TOWARD THE END OF THE PERIOD. THE 552-DM SPAGHETTI PLOT SHOWS THE 00Z GEFS MEMBERS ARE A TAD QUICKER THAN THE 00Z ECMWF ENSEMBLE MEMBERS. THIS APPEARS TO BE THE CASE THE PAST TWO MODEL CYCLES. WILL SPLIT BETWEEN THE TWO CAMPS AT THIS POINT WHICH WOULD FAVOR A BLEND OF THE 12Z GFS/00Z ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER