MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 238 PM EDT FRI SEP 18 2015 VALID SEP 18/1200 UTC THRU SEP 22/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. UPPER TROUGH AND SURFACE LOW(S) OFF EAST COAST OF U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN CONFIDENCE: BELOW AVERAGE THE STRONGER 12Z NAM IS IN THE MINORITY OF ENSEMBLE GUIDANCE AND UNSUPPORTED IN THE LATEST DETERMINISTIC MODEL SUITE. THERE IS A DIVISION AMONG THE GFS/GEFS SOLUTIONS AND THE ECMWF/ECENS SOLUTIONS REGARDING THE PLACEMENT OF THE SURFACE LOW WITH THE DETERMINISTIC ECMWF AND ECMWF-BASED ENSEMBLE MEMBERS HOLDING ONTO A PRIMARY LOW PRESSURE CENTER FARTHER SOUTH OFF OF THE SOUTHEAST COAST WHILE THE GFS/GEFS ACCELERATE THE LOW NORTHEASTWARD...WITH PERHAPS A WEAKER LOW LEFT BEHIND OFF OF THE SOUTHEAST COAST. THERE APPEARS TO BE GREATER SUPPORT FROM THE AVAILABLE GUIDANCE FOR AN EVOLUTION CLOSER TO THE ECMWF...OR ECMWF MEAN...WITH THE MORE DOMINANT LOW HANGING DOWN ACROSS THE SOUTH WITH THE STRONGER PROGRESSIVE SHORTWAVE "KICKERS" TO THE NORTH. THIS GENERAL IDEA IS SHOWN BY THE 12Z ECMWF/UKMET AND ALSO FITS IN WITH PREVIOUS WPC CONTINUITY. ALTHOUGH THE 12Z NUDGED TOWARD THE 12Z GFS...THE 12Z GFS/GEFS ARE STILL IN THE MINORITY. NGIVEN THE LARGE SPREAD SEEN...CONFIDENCE REMAINS BELOW AVERAGE. SHORTWAVE OVER SOUTH DAKOTA/NEBRASKA FRI AFTERNOON...WITH NEWD MOVING SFC LOW AND ATTENDANT COLD FRONT INTO THE WEEKEND ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE MODELS THAT WERE PREVIOUSLY DEEPER WITH THE SHORTWAVE TROUGH AS IT MOVES OVER THE GREAT LAKES HAVE TRENDED WEAKER...TOWARD THE MORE CONSISTENT RUNS OF THE GFS/ECMWF. CURRENTLY...THERE IS GOOD ENOUGH AGREEMENT IN THE LATEST MODELS TO PREFER A GENERAL MODEL COMPROMISE. LOW AMPLITUDE SHORTWAVE CROSSING THE N-CNTRL U.S. THROUGH THE WEEKEND WITH POSSIBLE CLOSED LOW INVOF THE OHIO VALLEY BY MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS SHOW REASONABLE AGREEMENT HERE...WITH THE 12Z CMC ADJUSTING ENOUGH TOWARD THE REMAINING CONSENSUS TO BE INCLUDED IN THE PREFERENCE OF A GENERAL MODEL COMPROMISE. CLOSED LOW POSSIBLY AFFECTING SRN CALIFORNIA BY EARLY NEXT WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS/UKMET BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE OUTSIDE OF THE ECMWF...THE 12Z MODELS HAVE CONTINUED A TREND TO BE CLOSER TO THE SOUTHWEST U.S. COAST BY MON EVENING WITH A CLOSED LOW WEST OF THE BAJA PENINSULA. THE ENSEMBLES SHOW THE ECMWF MORE OFFSHORE COMPARED TO THE REMAINING GEFS/CMC ENSEMBLES. THE DETERMINISTIC MODELS ARE THE SAME...WITH THE ECWMF THE FARTHEST OFFSHORE WITH THE CLOSED LOW. THE 12Z CMC IS THE MOST AGGRESSIVE WITH LOW PRESSURE OFF OF THE MEXICAN COAST AND WILL NOT BE INCLUDED IN THE PREFERENCE. WHILE THE ECMWF IS FARTHER OFFSHORE...AND NOT PREFERRED...A CONSENSUS OF ALL OF THE MODELS SUPPORT ANOMALOUS MOISTURE SPREADING INTO THE SOUTHWEST U.S. ZONAL ONSHORE FLOW INTO THE PACIFIC NORTHWEST WITH EMBEDDED SHORTWAVE INTO BRITISH COLUMBIA ON SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 12Z ECMWF BLEND CONFIDENCE: AVERAGE THE BIGGEST DIFFERENCES WITHIN THE ZONAL FLOW ARE TIED TO A SHORTWAVE FORECAST TO REACH BRITISH COLUMBIA ON SUN WITH THE GFS/ECMWF FALLING WITHIN THE MIDDLE OF THE LATEST SPREAD. THIS APPLIES TO THE MID-UPPER LEVEL SHORTWAVE AND SURFACE REFLECTION AND COLD FRONT MOVING INTO THE NWRN CONUS. LITTLE CHANGE WAS SEEN BETWEEN THE 12Z AND 00Z ECMWF RUNS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO