MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1226 AM EDT SAT SEP 12 2015 VALID SEP 12/0000 UTC THRU SEP 15/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...SHORTWAVE TROUGH INFLUENCING CALIFORNIA/SOUTHWEST THIS WEEKEND... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS DEPICT A SIMILAR LARGE SCALE EVOLUTION OF THIS SYSTEM THROUGH THE WEEKEND. ...CLOSED LOW SETTING UP OVER THE OHIO VALLEY BY SAT EVENING... ...LOW PRESSURE DEVELOPING OVER THE MID-ATLANTIC REGION... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF...THROUGH 48 HOURS 12Z ECMWF...AFTER 48 HOURS CONFIDENCE: AVERAGE THE MODELS ARE COMING INTO BETTER AGREEMENT WITH THE DETAILS OF THE CLOSED LOW THAT IS FORECAST TO AMPLIFY ACROSS THE OH VALLEY ON SAT AND THEN PIVOT THROUGH THE NORTHEAST THROUGH SUN AND MON. THIS WILL DRIVE DEVELOPING LOW PRESSURE OVER THE MID-ATLANTIC REGION TO THE NORTH AND THEN ACROSS NEW ENGLAND THROUGH MON. DESPITE IMPROVED MASS FIELD AGREEMENT...THE 00Z GFS DOES GRADUALLY BECOMES A BIT FASTER THAN THE MULTI-MODEL CONSENSUS AS THE UPPER LOW CROSS NORTHERN NEW ENGLAND ON MON. MEANWHILE...THE 12Z CMC BECOMES THE SLOWEST SOLUTION BY THAT TIME-FRAME. THE 12Z ECMWF/12Z UKMET AND 00Z NAM ALL SPLIT THE DIFF AND CLUSTER IN BETWEEN WITH TIMING. REGARDING DEPTH...THE 12Z UKMET APPEARS TO BE A LITTLE TOO WEAK WITH ITS SOLUTION ALOFT...BUT AT THE SURFACE THERE IS STRONGER AGREEMENT WITH THE DETAILS OF THE SURFACE LOW EVOLUTION. HOWEVER...THE 00Z GFS AFTER ABOUT 48 HOURS APPEARS TO AGAIN BE TOO PROGRESSIVE. THUS...WILL PREFER A BLEND OF THE 00Z GFS AND 12Z ECMWF THROUGH ABOUT 48 HOURS...AND THEN LEAN TOWARD THE 12Z ECMWF THEREAFTER. ...SHORTWAVE DROPPING SOUTHEAST TOWARD THE WEST COAST BY MON... ...LOW PRESSURE DEVELOPING IN THE LEE OF THE NORTHERN ROCKIES... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE THE 12Z UKMET REMAINS THE FASTEST SOLUTION WITH THE SYSTEM AS IT MOVES INTO THE NORTHWEST...WITH THE 12Z CMC AND 00Z NAM SOLUTIONS THE SLOWEST. STRONGER MODEL CLUSTERING AND ENSEMBLE SUPPORT RESIDES WITH THE 00Z GFS AND 12Z ECMWF WHICH SPLIT THE DIFFERENCE BETWEEN THE FASTER UKMET AND SLOWER CMC. A BLEND OF THE GFS AND ECMWF WILL BE PREFERRED AND THIS WILL ALSO APPLY TO THE DETAILS OF DEVELOPING SURFACE LOW PRESSURE IN THE LEE OF THE NORTHERN ROCKIES ON MON. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON