MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 119 PM EDT TUE OCT 20 2015 VALID OCT 20/1200 UTC THRU OCT 24/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES AND CONFIDENCE ...UPPER LOW/TROUGH MOVING ACROSS EASTERN CANADA... ...FRONT STALLING ACROSS THE NORTHEAST AHEAD OF NEXT SURFACE WAVE... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODELS REMAIN IN GOOD AGREEMENT BOTH WITH RESPECT TO THE UPPER TROUGH/LOW MOVING ACROSS QUEBEC AND ATLANTIC CANADA WED-THU AND THE ASSOCIATED FRONTAL BOUNDARY REMAINING ACROSS THE NORTHEASTERN U.S. BACK INTO THE UPPER MIDWEST AHEAD OF THE NEXT SURFACE WAVE. ...NORTHERN STREAM SHORTWAVE CROSSING THE NORTHERN TIER STATES THROUGH FRI... ...LOW PRESSURE DEVELOPING OVER THE PLAINS AND DEEPENING TOWARD SOUTHEAST CANADA... PREFERENCE: 12Z MODEL BLEND CONFIDENCE: AVERAGE THROUGH EARLY THU THE MODELS ARE IN FAIRLY GOOD AGREEMENT AS THIS SYSTEM DEEPENS AND MOVES TOWARD THE UPPER GREAT LAKES. THE UKMET WHICH WAS A RELATIVE OUTLIER WITH ITS 00Z RUN HAS TRENDED A LITTLE FURTHER TO THE NORTH...PUTTING IT IN BETTER AGREEMENT WITH THE NAM/GFS WHICH HAVE REMAINED FAIRLY CONSISTENT. SIGNIFICANT DIFFERENCES DO NOT EMERGE UNTIL LATE IN THE PERIOD WHEN THE 12Z MODELS BEGIN TO OUTPACE THE OLDER GUIDANCE ACROSS ATLANTIC CANADA. ...UPPER TROUGH AND COLD FRONT ENTERING THE PACIFIC NORTHWEST/NORTHERN ROCKIES WED/THURS AND REACHING THE GREAT BASIN ON FRI... PREFERENCE: 00Z ECMWF CONFIDENCE: AVERAGE FOR A PERIOD THE 12Z GFS BECOMES A RELATIVELY SLOWER AND MORE AMPLIFIED SOLUTION ACROSS THE PACIFIC NORTHWEST INTO THE GREAT BASIN THU INTO EARLY FRI...WHILE THE UKMET REMAINS A RELATIVELY FASTER OUTLIER. THE NAM AND THE 00Z ECMWF FALL CLOSE TO THE MIDDLE OF THE CURRENT MODEL SPREAD. ...UPPER TROUGH/CLOSED LOW DIGGING THROUGH THE SOUTHWEST/FOUR CORNERS REGION... ...LEE-SIDE TROUGH/LOW DEVELOPMENT IMPACTING THE HIGH PLAINS... PREFERENCE: NAM/GFS/00Z ECMWF CONFIDENCE: ABOVE AVERAGE DIFFICULT TO DISCOUNT THE NAM/GFS/00Z ECMWF...WHICH ALL CONTINUE TO HANDLE THIS SYSTEM SIMILARLY THROUGH FRI. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... PEREIRA