MODEL DIAGNOSTIC DISCUSSION...AMENDED NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1125 PM EST THU JAN 16 2014 VALID JAN 17/0000 UTC THRU JAN 20/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. PACIFIC SYSTEM MOVING INTO THE PLAINS/MIDWEST LATE SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CANADIAN COMPROMISE CONFIDENCE: AVERAGE THE 12Z CANADIAN WAS SLOWER/DEEPER WITH THIS SYSTEM AS IT MOVES OVER THE TOP OF RIDGING NEAR THE WESTERN COAST OF CANADA SATURDAY NIGHT, WHICH IS COMPLETELY AGAINST WHAT ONE WOULD EXPECT AS A SYSTEM MOVES OVER THE TOP OF THE RIDGE. THIS LEADS TO A STRONGER/SLOWER MOVING LOW MOVING INTO THE NORTHERN PLAINS SUNDAY NIGHT IN THE 12Z CANADIAN THAN SEEN IN THE OTHER GUIDANCE. USING THE PATTERN AS A GUIDE, PREFER A NON-CANADIAN COMPROMISE WITH AVERAGE CONFIDENCE CONSIDERING THE SYSTEM'S PROGRESSIVE NATURE. POLAR VORTEX SECTION SETTLING INTO QUEBEC EARLY MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/UKMET/ECMWF COMPROMISE CONFIDENCE: ABOVE AVERAGE ALOFT, THE 12Z CANADIAN IS THE FARTHEST NORTH WITH THE MID-TROPOSPHERIC PORTION OF THIS SYSTEM DUE TO A WEAKER RIDGE UPSTREAM ACROSS WESTERN CANADA, WHICH IS WEAKER THAN BOTH THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS. SINCE DETERMINISTIC GUIDANCE CAN BREAK DOWN AMPLIFIED PATTERNS TOO QUICKLY, AND THIS RIDGE HAS BEEN MORE OR LESS IN PLACE FOR THE PAST COUPLE MONTHS, BELIEVE THE CANADIAN IS ERRANT HERE. AT THE SURFACE, THE 00Z NAM BECOMES TOO FAR NORTH WITH ITS LOW PRESSURE SYSTEM NORTH OF MAINE, LYING ON THE NORTHWEST CORNER OF THE 12Z GLOBAL ENSEMBLE SPREAD. DUE TO THE ABOVE, PREFER A 00Z GFS/12Z UKMET/12Z ECMWF COMPROMISE HERE WITH ABOVE AVERAGE CONFIDENCE DUE TO ITS RELATIVELY STABLE POSITION WITHIN THE GENERAL FLOW PATTERN. SHORTWAVE DROPPING INTO TEXAS LATE SUNDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/ECMWF COMPROMISE CONFIDENCE: AVERAGE THE 12Z UKMET WAS THE QUICKEST WITH THIS SYSTEM WHILE THE 12Z CANADIAN WAS THE SLOWEST DUE TO ITS BEHAVIOR WITH A SYSTEM MOVING INTO/THROUGH THE NORTHERN PLAINS. THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS SUPPORT THE INTERMEDIATE 00Z GFS/12Z ECMWF GUIDANCE HERE -- A COMPROMISE OF WHICH IS PREFERRED WITH AVERAGE CONFIDENCE CONSIDERING ITS PROGRESSIVE NATURE. SYSTEM MOVING THROUGH THE EAST EARLY SUNDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE DIFFERENCES REGARDING THIS SYSTEM HAVE VANISHED SINCE THIS TIME YESTERDAY. A GENERAL MODEL COMPROMISE IS PREFERRED TO DEAL WITH ANY LINGERING DETAIL ISSUES WITH AVERAGE CONFIDENCE CONSIDERING ITS PROGRESSIVE NATURE. SHORTWAVE MOVING FROM IOWA OFFSHORE ATLANTIC COAST SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM COMPROMISE CONFIDENCE: AVERAGE WHILE SURFACE-BASED ISSUES APPEAR MINIMAL WITH THIS SYSTEM, THERE ARE SUBTLE DEPTH ISSUES, MOST OBVIOUS AT THE 700 HPA LEVEL (AND TO SOME DEGREE 500 HPA) FROM LATE FRIDAY ONWARD, WHEN THE 00Z NAM BECOMES STRONGER THAN THE OTHER GUIDANCE WITH THIS SYSTEM WHICH AFFECTS ITS PRECIPITATION PATTERN. IT APPEARS THE NAM IS SLOWER IN MOVING AN UPSTREAM IMPULSE TOWARDS THIS SYSTEM, WHICH ALLOWS IT TO BE DEEPER AND SLOWER MOVING. SINCE THE NAM CAN BE A DEEP OUTLIER WITH SYSTEMS, AND THE GENERAL FLOW PATTERN SUPPORTS SWIFT MOVEMENT, PREFER A NON-NAM COMPROMISE WITH AVERAGE CONFIDENCE CONSIDERING THE SYSTEM'S PROGRESSIVE NATURE. www.wpc.ncep.noaa.gov/html/model2.shtml... ROTH