MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1223 AM EDT WED SEP 28 2016 VALID SEP 28/0000 UTC THRU OCT 01/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. BINARY INTERACTION NEAR THE WEST COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: BELOW AVERAGE THERE ARE MODEST DIFFERENCES ALOFT NEAR AND OFFSHORE THE WEST COAST WHICH HAVE SOME BEARING ON THE MOVEMENT OF THE SYSTEM IN THE MIDWEST/OHIO VALLEY. THE 12Z CANADIAN/00Z GFS ARE THE SLOWEST/MOST AMPLIFIED WITH THE TROUGH NEAR CA FRIDAY NIGHT, WHILE THE 00Z GFS/12Z UKMET ARE THE MOST NORTHERLY WITH THE DEEP CYCLONE OFFSHORE SOUTHWEST CANADA. THE GFS MAKES INTERNAL SENSE AS ITS CLOSED LOW OFFSHORE HAIDA GWAII AND VANCOUVER ISLANDS IS FARTHER NORTH, IMPLYING LESS INTERACTION BETWEEN THE TWO. HOWEVER, BINARY/FUJIWHARA INTERACTIONS SUCH AS THESE ARE TRICKY, AND LEAD TO BELOW AVERAGE FORECAST CONFIDENCE. FOR THE TIME BEING, PREFER A COMPROMISE OF THE AVAILABLE GUIDANCE. DEEP CYCLONE ACROSS MIDWEST DOUBLING BACK TOWARDS MI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-GFS COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE THE 00Z GFS ENDS UP BEING THE FARTHEST SOUTH WITH THIS SYSTEM BY FRIDAY NIGHT. THIS APPEARS TO BE DUE TO ITS SLOWER UPPER TROUGH OFFSHORE THE WEST COAST AND DOWNSTREAM RIDGING ACROSS THE PLAINS WHICH IS MORE ENHANCED THAN MUCH OF THE GUIDANCE. WE HAVE TWO COMPETING INFLUENCES WITH THIS SYSTEM'S MOVEMENT -- THE STRONG/NORTHERLY DISPLACED SUBTROPICAL RIDGE NORTH OF THE SARGASSO SEA AND THE UPSTREAM TROUGH/RIDGE COUPLET. NO MATTER WHICH SOLUTION YOU PICK, THE ATLANTIC RIDGE IS STRONG AND SHOULD LEAD TO SOME NORTHERLY RETURN AFTER THURSDAY NIGHT AS THE RIDGE IN THE PLAINS IS WEAKENED BY A SHORTWAVE MOVING THROUGH MT. FOR NOW, WILL CONSIDER THE 00Z GFS A LOWER PROBABILITY ALTERNATIVE SCENARIO AND GO WITH A COMPROMISE OF THE CONSENSUS -- THE 12Z UKMET/12Z ECMWF/00Z NAM/12Z CANADIAN -- WITH SLIGHTLY BELOW AVERAGE CONFIDENCE. CLOSED LOW LIFTING OUT OF THE SOUTHWEST SHORTWAVE LIFTING MOVING THROUGH MT EARLY FRI MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE SYSTEMS. A COMPROMISE OF THE AVAILABLE GUIDANCE IS PREFERRED TO DEAL WITH ANY LINGERING DETAIL ISSUES WITH ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ROTH