MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1236 AM EDT THU SEP 10 2015 VALID SEP 10/0000 UTC THRU SEP 13/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...MID LEVEL TROUGH OFF THE COAST OF CALIFORNIA BY SAT AND SUN... PREFERENCE: NON 12Z UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE NO MAJOR CHANGES FROM THE PREVIOUS THINKING...THE MODELS ARE GENERALLY IN GOOD AGREEMENT WITH THE EVOLUTION OF A MID LEVEL TROUGH JUST OFF THE COAST OF CA THIS WEEKEND. THE 12Z UKMET APPEARS OVERALL TO BE A LITTLE TOO WEAK WITH THE FEATURE THOUGH...AND SO A NON-UKMET CONSENSUS WILL BE PREFERRED. ...COLD FRONT MOVING INTO THE NORTHEAST/MID-ATLANTIC THROUGH THURS... ...FRONTAL WAVE MOVING FROM THE MID-ATLANTIC TO OFFSHORE NEW ENGLAND... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: ABOVE AVERAGE THE LATEST MODELS CONTINUE TO SHOW GOOD AGREEMENT WITH COLD FRONTAL TIMING ACROSS THE MID-ATLANTIC AND NORTHEAST THROUGH THURS. ALL THE WHILE...A WAVE OF LOW PRESSURE DEVELOPING ALONG THE FRONT OVER THE MID-ATLANTIC COASTAL PLAIN EARLY THURS IS FORECAST TO LIFT NORTHEAST AND OFFSHORE NEW ENGLAND ON FRI. THE 00Z NAM AND 12Z CMC TUCK THEIR RESPECTIVE SURFACE LOWS A TAD LEFT OF THE MULTI-MODEL CONSENSUS ON FRI. THE 00Z GFS AND 12Z ECMWF ARE A LITTLE FARTHER EAST WHICH THE 12Z UKMET TENDED TO SUPPORT AS WELL. OVERALL...THERE IS NOT A TREMENDOUS AMOUNT OF MASS FIELD SPREAD...BUT BASED ON STRONGER MODEL CLUSTERING...A BLEND OF THE 00Z GFS AND 12Z ECMWF WILL BE PREFERRED. ...CLOSED LOW SETTING UP OVER THE OHIO VALLEY BY SAT EVENING... ...LOW PRESSURE DEVELOPING OVER THE MID-ATLANTIC REGION... PREFERENCE: BLEND OF THE 12Z UKMET/12Z ECENS MEAN/18Z GEFS MEAN CONFIDENCE: BELOW AVERAGE ALL OF THE MODELS SHOW SHORTWAVE ENERGY DIGGING SOUTHEAST THROUGH THE MIDWEST AND AMPLIFYING INTO A CLOSED UPPER LOW ACROSS THE OH VALLEY SAT AND SUN. MEANWHILE...THE HEIGHT FALLS WILL BE DEVELOPING SURFACE LOW PRESSURE OVER THE MID-ATLANTIC REGION IN THE IMMEDIATE LEE OF THE CENTRAL APPALACHIANS. DIFFERENCES IN THE MODELS BECOME RATHER SIGNIFICANT AT THE SURFACE AND ALOFT BY THE END OF THE PERIOD...AS THE 12Z CMC SUGGESTS A NOTABLY STRONGER UPPER LOW OVER THE OH VALLEY COMPARED TO THE REMAINING GUIDANCE. THE STRONGER CMC ALSO WRAPS SURFACE LOW PRESSURE NORTHWEST BACK ACROSS THE UPPER OH VALLEY AND INTO THE LOWER GREAT LAKES REGION. MEANWHILE...THE 00Z NAM TENDS TO BE THE WEAKEST SOLUTION ALOFT AND HAS A WEAKER SURFACE LOW REFLECTION. IT IS ALSO A LITTLE MORE PROGRESSIVE. LIKE THE NAM...THE 00Z GFS IS ALSO A BIT MORE PROGRESSIVE AND A BIT WEAKER AS WELL. THE 12Z UKMET AND 12Z ECMWF ARE A BIT SLOWER AND IN BETWEEN THE SLOWER CMC AND FASTER NAM/GFS SOLUTIONS. HOWEVER...THE ECMWF WRAPS ITS SURFACE LOW CENTER WELL BACK TO THE NORTHWEST TOWARD THE LOWER GREAT LAKES REGION IN A SIMILAR WAY THAT THE CMC DOES. BASED ON THE LATEST ENSEMBLE OUTPUT...THE CMC AND ECMWF LOW PLACEMENTS ARE OUTLIER SOLUTIONS. THE GFS AND NAM BOTH APPEAR TOO PROGRESSIVE AND WEAK. THE LATEST GEFS MEAN AND ECENS MEAN CLUSTER TOGETHER QUITE WELL AND CLOSE TO THE UKMET SOLUTION...AND A BLEND OF THESE SOLUTIONS WILL BE PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON