MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1255 AM EDT SUN OCT 05 2014 VALID OCT 05/0000 UTC THRU OCT 08/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...HURRICANE SIMON... PREFERENCE: 12Z ECMWF SIMON...CHURNING UP THE WATERS OF THE EASTERN PACIFIC...WAS A MAJOR HURRICANE SATURDAY EVENING WITH A MINIMUM CENTRAL PRESSURE ESTIMATED AT 946 MB. THE CYCLONE IS FORECAST TO HAVE PEAKED...AND TO LOSE INTENSITY AS IT TRACKS OVER COOLER WATERS AND RECURVES TOWARD THE BAJA PENINSULA OVER THE NEXT FEW DAYS. PLEASE SEE NATIONAL HURRICANE CENTER ADVISORIES FOR A MORE DETAILED DISCUSSION. IN TERMS OF LARGE SCALE MODEL GUIDANCE...THE 12Z ECMWF BEST FITS THE OFFICIAL NHC FORECAST TRACK. THE ECMWF...ALONG WITH OTHER GUIDANCE...DOES BRING MOISTURE AND RAINFALL TOWARD THE SOUTHWEST U.S. BY TUESDAY...ALTHOUGH THERE IS A GREAT DEAL OF MODEL SPREAD REGARDING THE DETAILS. CONSISTENTLY THE GFS/GEFS HAVE SET A MUCH FASTER PACE FOR BOTH THE LOW LEVEL CYCLONE AND ITS ASSOCIATED MOISTURE TO RECURVE AND ACCELERATE TOWARD THE SOUTHWEST U.S. OTHER GUIDANCE...SUCH AS THE MOST RECENT 00Z NAM AND SEVERAL RUNS OF THE UKMET AND CANADIAN...ARE RELUCTANT TO BRING THE STORM EASTWARD AT ALL...PREFERRING A SLOW DRIFT NORTHWARD OFFSHORE OF BAJA. AGAIN...THE ECMWF IS SOMETHING OF A MIDDLE GROUND. SCATTER PLOTS COMBINING LOW TRACKS FROM ALL THE MAJOR ENSEMBLE SYSTEMS DO SHOW A TREND TO THE EAST...BUT WITH THE ECMWF STILL RIGHT IN THE MIDDLE OF THE SPREAD...AND THE GFS AT THE FAST/FAR RIGHT SIDE. A MID LATITUDE TROUGH TO THE NORTH IS NOT PARTICULARLY STRONG...NOR IN PARTICULARLY CLOSE PROXIMITY...BUT INTERACTION IS LIKELY TO INCREASE BETWEEN THIS TROUGH AND SIMON OVER TIME. ...FULL LATITUDE TROUGH AFFECTING EASTERN NORTH AMERICA... PREFERENCE: BLEND OF 00Z NAM/12Z ECMWF WITH A STACKED CYCLONE IN PLACE OVER ONTARIO...SHORTWAVES SHOULD PRODUCE MINOR WOBBLES OF THE VORTICITY CENTER AND ASSOCIATED SURFACE LOW...AS WE HAVE SEEN THE PAST 24-36 HOURS. RUNS OF THE GFS...AND OCCASIONALLY THE ECMWF...HAVE EXAGGERATED CERTAIN SHORTWAVES TO TUG THE SYSTEM ONE DIRECTION OR ANOTHER...BUT WITH LITTLE RUN TO RUN CONTINUITY. OVER THE PAST COUPLE OF CYCLES THE NAM AND ECMWF HAVE SHOWN THE BEST CONTINUITY AND THEY ARE CLOSE TO THE ENSEMBLE MEANS...ESPECIALLY THE ECMWF ENSEMBLE MEAN...WHEREAS THE GEFS HAS BEEN MORE SUSCEPTIBLE TO THESE OCCASIONALLY EXAGGERATED SHORTWAVES. ...WEAK UPPER TROUGH OFF THE CALIFORNIA COAST... PREFERENCE: 12Z ECMWF THE GFS FORECASTS THE MOST EXPANSIVE INFLUENCE OF THIS SYSTEM...AND RAPID INTERACTION BETWEEN THIS TROUGH AND HURRICANE SIMON TO ITS SOUTHEAST. THE OTHER MODELS DEPICT A MORE NARROWLY DEFINED TROUGH THAT SLOWLY EXPANDS AND MOVES TO THE SOUTHEAST. IN GENERAL...A NON-GFS SOLUTION IS PREFERRED...AND THE SAFEST INDIVIDUAL CHOICE AT THIS TIME IS THE 12Z ECMWF TO REMAIN CONSISTENT WITH THE NHC FORECAST TRACK FOR SIMON. ...FLAT FLOW IN THE PACIFIC NORTHWEST... PREFERENCE: BLEND OF 00Z GFS WITH 12Z ECMWF/CANADIAN LITTLE IMPACTFUL WEATHER IS EXPECTED HERE THROUGH TUESDAY AS EASTWARD-MOVING SHORTWAVE TROUGHS DAMPEN WITHIN A MEAN SHORTWAVE RIDGE POSITION. THERE ARE NO STRONG OUTLIERS BUT THE NAM IS COLDER THAN CONSENSUS IN ITS MID LEVEL THERMAL FIELDS AND THE UKMET IS A BIT STRONGER WITH A SHORTWAVE APPROACHING THE PAC NW COAST BY 08/12Z. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE