MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1252 AM EDT SAT MAY 16 2015 VALID MAY 16/0000 UTC THRU MAY 19/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...SHORTWAVE CLIPPING UPPER NEW ENGLAND BY SUNDAY MORNING... ...SURFACE WAVE DEVELOPING OFF THE COAST... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE MODELS SHOW A FEATURE IN THE NORTHERN STREAM WILL DIP DOWN GRAZING SECTIONS OF NORTHERN ME BY EARLY SUNDAY. THERE ARE SOME MINOR DIFFERENCES WITH THE POSITION OF THIS SHORTWAVE BUT THESE DO NOT APPEAR TO AFFECT THE FORECAST. LIKEWISE...PRETTY STRONG AGREEMENT EXISTS WITH THE SURFACE DEVELOPMENT THAT A GENERAL MODEL COMPROMISE IS WARRANTED HERE. ...DEEP UPPER TROF EXTENDING ACROSS THE WESTERN/CENTRAL U.S... ...STRONG SURFACE CYCLONE MOVING TOWARD THE UPPER GREAT LAKES BY 18/1800Z... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A FULL-LATITUDE TROF EXTENDING FROM THE WESTERN U.S. INTO THE ROCKIES WILL CONTINUE TO MOVE EASTWARD IN TIME CARRYING A SHARP AREA OF MID-LEVEL HEIGHT FALLS INTO THE PLAINS. THERE WILL BE A MULTITUDE OF SMALLER-SCALE IMPULSES CIRCULATING AROUND THIS UPPER LOW WITH THESE DETAILS NOT EASILY RESOLVED. THROUGH 18/0000Z...MODELS SHOW A FAIR AMOUNT OF AGREEMENT WITH THE UPPER AND SURFACE PATTERNS. THE EXCEPTION IS THE 00Z NAM WHICH IS WEAKER ALOFT NOT CARRYING A 558-DM HEIGHT CONTOUR BY SUNDAY EVENING ACROSS THE UPPER MIDWEST. EVENTUALLY THE 00Z NAM ALSO BECOMES QUICKER IN SLIDING THE SHORTWAVE TOWARD THE GREAT LAKES REGION THE FOLLOWING DAY. WHILE THE REMAINING MODELS LOOK REASONABLE...WILL FAVOR THE 00Z GFS/12Z ECMWF AS THEY DO STICK CLOSER TO THE ENSEMBLE MEANS THROUGHOUT THE DAY 2/3 TIME FRAME. ...BROAD UPPER LOW MOVING INTO THE SOUTHWESTERN CONUS BY 19/1200Z... PRELIMINARY PREFERENCE: NON-12Z UKMET MODEL CONSENSUS FORECAST CONFIDENCE: ABOVE AVERAGE TOWARD THE END OF THE PERIOD...ANOTHER UPPER TROF TAKES SHAPE ACROSS THE SOUTHWESTERN U.S. THE MODELS CLUSTER QUITE WELL WITH THIS FEATURE EXCEPT FOR THE 12Z UKMET WHICH IS DISPLACED TOWARD THE EAST. WILL LEAN ON A NON-12Z UKMET MODEL CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER