MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1215 AM EDT FRI AUG 07 2015 VALID AUG 07/0000 UTC THRU AUG 10/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...SHORTWAVE TROUGH CROSSING THE MID-ATLANTIC/SOUTHEAST... ...SURFACE LOW IMPACTING THE EAST COAST... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE THE MODELS ARE IN GOOD AGREEMENT WITH THE SHORTWAVE CROSSING THE CAROLINAS ON FRI AND THEN MOVING OFFSHORE ON SAT. AN ACCOMPANYING AREA OF LOW PRESSURE WILL MOVE OFFSHORE BY SAT AND THEN LIFT NORTHEAST OFFSHORE NEW ENGLAND IN AN ELONGATED FASHION. THE 00Z NAM SUGGESTS A STRONGER SURFACE LOW EVOLUTION OFFSHORE. MEANWHILE...THE 12Z UKMET IS THE FASTEST TO LIFT ITS LOW CENTER TO THE NORTHEAST AND AWAY FROM THE EAST COAST. THE STRONGER MODEL CLUSTERING OVERALL FAVORS A BLEND OF THE 00Z GFS AND 12Z ECMWF...AND A BLEND OF THESE SOLUTION WILL BE PREFERRED GIVEN STRONGER ENSEMBLE SUPPORT FROM THE GEFS MEAN AND ECENS MEAN. ...SHORTWAVE EJECTING ACROSS THE UPPER MIDWEST/GREAT LAKES FRI/SAT... ...TROUGH ADVANCING INTO THE NORTHEAST... PREFERENCE: NON-ECMWF CONSENSUS CONFIDENCE: AVERAGE THE SHORTWAVE ENERGY AND ASSOCIATED SURFACE LOW CURRENTLY MOVING ACROSS THE UPPER MIDWEST WILL EVENTUALLY PLAY A ROLE IN THE REINFORCEMENT OF A TROUGH OVER THE NORTHEAST BY SAT. THE MODELS DIVERGE PRETTY QUICKLY ON THEIR EVOLUTION OF THE SURFACE WAVE AS IT APPROACHES THE UPPER GREAT LAKES REGION ON FRI. THE 00Z NAM AND TO A LESSER EXTENT THE 00Z GFS ARE QUICK TO DAMPEN THE SURFACE LOW OUT...BUT THE 12Z UKMET/12Z CMC AND ESPECIALLY THE 12Z ECMWF HANG ONTO A STRONGER WAVE AT LEAST INTO SAT BEFORE WEAKENING. THE ECMWF ACTUALLY TAKES ITS LOW CENTER DOWN ACROSS LOWER MI BEFORE DISSIPATING IT. ALL OF THE MODELS TAKE THE REMNANTS OF THE SHORTWAVE ENERGY INTO THE NORTHEAST ON SUN...WITH THE ECMWF THE SLOWEST AND DEEPEST. THE REMAINING MODELS ARE CLUSTERED AROUND A MORE PROGRESSIVE AND SOMEWHAT WEAKER TROUGH EVOLUTION. THE LATEST ECENS MEAN AND GEFS MEAN BOTH SUGGEST THE 12Z ECMWF IS TOO SLOW AND TOO DEEP. BASED ON THIS...A NON-ECMWF CONSENSUS WILL BE PREFERRED. ...UPPER TROUGH OVER THE NORTHWEST MOVING EAST ACROSS SOUTHERN CANADA FRI/SAT... ...TROUGH AMPLIFYING INTO THE GREAT LAKES ON SUN/MON... PREFERENCE: BLEND OF THE 18Z GEFS MEAN AND 12Z ECENS MEAN CONFIDENCE: AVERAGE THE MODELS TAKE THE CURRENT UPPER TROUGH SKIRTING THE NORTHERN HIGH PLAINS AND SOUTHERN ALBERTA/SASKATCHEWAN OFF TO THE EAST OVER THE NEXT COUPLE OF DAYS AND THEN DIG THE TROUGH INTO THE GREAT LAKES REGION SUN AND MON. THIS WILL DRIVE ONE SURFACE LOW EAST ACROSS SOUTHERN CANADA WHILE ANOTHER WAVE LIFTS NORTHEAST OUT OF THE CENTRAL PLAINS AND INTO THE UPPER OH VALLEY OR LOWER GREAT LAKES REGION BY EARLY MON. THE 12Z UKMET OVERALL IS THE WEAKEST AND A TAD MORE PROGRESSIVE WITH THE TROUGH EVOLUTION...WITH THE 00Z NAM THE SLOWEST BY MON. REGARDING THE SURFACE LOWS...THE 00Z NAM/12Z CMC AND 12Z UKMET ALL HAVE WELL-DEFINED LOWS MOVING EAST TOWARD LOWER MI BY EARLY MON. THE 00Z GFS AND 12Z ECMWF ARE WEAKER AND LESS DEFINED WITH THIS. HOWEVER...THE LATEST GEFS MEAN AND ECENS MEAN SUGGEST THE DETERMINISTIC GFS/ECMWF SOLUTIONS MAY BE A BIT TOO WEAK. WILL PREFER A COMPROMISE WITH THE ENSEMBLE MEANS AS A RESULT AT THIS POINT. ...UPPER TROUGH MOVING INTO CALIFORNIA/GREAT BASIN TODAY INTO THE WEEKEND... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: ABOVE AVERAGE OVERALL MINOR DIFFERENCES EXIST WITH REGARD TO TIMING/LOCATION OF THIS WAVE AS IT TRACKS ACROSS CALIFORNIA AND EVENTUALLY NORTHWEST INTO THE NORTHERN PLAINS BY SUNDAY...BUT THE 00Z NAM DOES TEND TO BE A TAD STRONGER THAN THE MULTI-MODEL CONSENSUS...AND SO A NON-NAM CONSENSUS WILL BE PREFERRED. ...UPPER TROUGH DIGGING TOWARD BRITISH COLUMBIA/PACIFIC NORTHWEST THIS WEEKEND... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN VERY GOOD AGREEMENT IN TAKING AN UPPER LOW SOUTHEAST FROM THE GULF OF AK TOWARDS COASTAL AREAS OF BRITISH COLUMBIA BY SUN WITH HEIGHT FALLS BEGINNING TO OVERSPREAD THE PACIFIC NORTHWEST. THE 12Z UKMET IS A BIT OF A FASTER OUTLIER BY THE END OF THE PERIOD...WITH THE REMAINING MODELS SHOWING BETTER AGREEMENT. THE BEST CLUSTERING FAVORS A BLEND OF THE 00Z GFS AND 12Z ECMWF...SO A BLEND OF THESE TWO SOLUTIONS WILL BE PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON