MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 230 PM EDT FRI OCT 16 2015 VALID OCT 16/1200 UTC THRU OCT 20/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM, GFS, AND UKMET MODEL INITIALIZATION ERRORS APPEARED NEGLIGIBLE WITH RESPECT TO THEIR FORECASTS ...SOUTHWEST U.S. UPPER LEVEL LOW... PREFERENCE: NON-UKMET CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE A WELL DEVELOPED UPPER LEVEL LOW CURRENTLY NEAR THE CENTRAL CALIFORNIA COASTLINE WILL BE THE MAIN WEATHER MAKER ACROSS THE SOUTHWESTERN U.S. THROUGH SATURDAY. GOOD AGREEMENT CONTINUES AMONG THE MODELS IN TAKING THIS SYSTEM GRADUALLY INLAND ACROSS CALIFORNIA THROUGH FRIDAY NIGHT AND THEN EAST ACROSS ARIZONA BY EARLY SATURDAY WHILE GRADUALLY BECOMING ABSORBED INTO THE MID AND UPPER LEVEL FLOW BY SUNDAY AFTERNOON OVER THE FOUR CORNERS REGION. THE 12Z UKMET APPEARS TO BE THE QUICKEST IN WEAKENING THE SYSTEM BEYOND 24 HOURS, SIMILAR TO ITS PREVIOUS RUN. THE REMAINING MODELS APPEAR WELL CLUSTERED THROUGH SATURDAY NIGHT WITH TIMING AND DEPTH. A NON-UKMET CONSENSUS WILL BE PREFERRED AT THIS POINT. ...UPPER TROUGH INFLUENCING THE WEST COAST THIS WEEKEND... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE ANOTHER PRONOUNCED UPPER LEVEL TROUGH AND SHORTWAVE IS PROGGED TO REACH THE WEST COAST BY THIS WEEKEND, WITH THE TROUGH AXIS EXPECTED TO REACH THE COAST SATURDAY NIGHT. SINCE YESTERDAY, THE GUIDANCE HAS COME INTO BETTER AGREEMENT IN DEPICTING ENERGY IN THE BASE OF THIS TROUGH AMPLIFYING INTO A CLOSED LOW AND SEPARATING AWAY FROM THE MAIN BELT OF THE WESTERLIES TO THE NORTH. THE 12Z CMC IS THE OUTLIER AMONG THE 12Z MODELS AND IT IS CONSIDERABLY DEEPER WITH THE 500MB HEIGHT PATTERN, WHEREAS THE 12Z NAM IS WEAKER AND SLIGHTLY SLOWER WITH THE TROUGH AXIS. THE 12Z GFS IS MORE PRONOUNCED WITH THE UPPER LEVEL COMPARED TO ITS MEAN, AND THIS ALSO HOLD TRUE FOR THE ECMWF. A COMPROMISE BETWEEN THE 12Z GFS,12Z ECMWF, AND GEFS MEAN WILL BE PREFERRED AT THIS POINT GIVEN THE CONTINUING UNCERTAINTY WITH THIS SYSTEM. ...SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST EARLY MONDAY... PREFERENCE: BLEND OF THE 12Z NAM/12Z UKMET AND 12Z ECMWF CONFIDENCE: NEAR AVERAGE THE GUIDANCE SHOWS A SHORTWAVE TROUGH APPROACHING BRITISH COLUMBIA AND THE PACIFIC NORTHWEST BY EARLY MONDAY. THE 00Z CMC IS CONSIDERABLY DEEPER WITH THE TROUGH THAN THE MULTI-MODEL CONSENSUS, AND THE GFS IS A LITTLE SLOW WITH THE PASSAGE OF THE TROUGH. THE 12Z NAM/12Z UKMET/00Z ECMWF ARE WELL CLUSTERED ON A SLIGHTLY FASTER SOLUTION, SO WE WILL FAVOR A BLEND OF THE NAM, UKMET, AND ECMWF AT THIS POINT. ...COLD FRONT CROSSING THE NORTHERN PLAINS AND UPPER MIDWEST BY MONDAY... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: NEAR AVERAGE THE MODELS AGREE VERY WELL IN BRINGING A COLD FRONT ACROSS THE NORTHERN PLAINS AND THEN TOWARD THE UPPER MIDWEST BY EARLY MONDAY. THE 12Z NAM TENDS TO BE SLIGHTLY SLOWER WITH THE FRONTAL TIMING THAN THE MODEL CONSENSUS, WHILE THE UKMET IS JUST SLIGHTLY MORE PROGRESSIVE. THE 12Z CMC/12Z ECMWF AND 12Z GFS SPLIT THE DIFFERENCE, SO WE WILL PREFER A BLEND AT THIS POINT OF THE 12Z GFS AND 12Z ECMWF. ...LOW PRESSURE TROUGH CROSSING NORTHERN NEW ENGLAND ON SATURDAY... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE MODELS ARE NOW IN VERY GOOD AGREEMENT WITH THIS SHORTWAVE IMPULSE AND ASSOCIATED SURFACE TROUGH THAT CROSSES NORTHERN NEW ENGLAND EARLY ON SATURDAY. THEREFORE A GENERAL MODEL COMPROMISE CAN BE USED HERE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAMRICK