MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 237 AM EDT WED MAY 20 2015 VALID MAY 20/0000 UTC THRU MAY 23/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z MODEL GUIDANCE ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...PERSISTENT UPPER TROF ANCHORING THE NORTHEASTERN SECTOR OF THE CONTINENT... ...SURFACE LOW EMERGING OFF THE CAROLINAS BY LATE THURSDAY NIGHT... FINAL PREFERENCE: BLEND OF THE 00Z NAM/ECMWF FORECAST CONFIDENCE: AVERAGE THE HIGH-LATITUDE BLOCK FEATURING POSITIVE HEIGHT ANOMALIES ACROSS ALBERTA WILL ALLOW BELOW NORMAL HEIGHTS TO PERSIST ACROSS EASTERN CANADA. A SERIES OF VORTICITY MAXIMA ARE EXPECTED TO TREK SOUTHWARD TOWARD THE GREAT LAKES BEFORE MOVING TOWARD NEW ENGLAND. TOWARD THE END OF THE PERIOD...EARLY SATURDAY...THE CORE OF LOWER HEIGHTS IS FORECAST TO CROSS UPPER NEW ENGLAND. THE MODEL MOST DIVERGENT TO THE CONSENSUS IS THE 00Z UKMET WHICH IS QUICKER WITH THE UPPER LOW ON FRIDAY/SATURDAY. ITS SOLUTION DID TREND WEST BUT IT STILL SEEMS TO BE DISPLACED FROM A MAJORITY OF THE OTHER MODELS. REGARDING THE EVOLVING SURFACE WAVE ACROSS THE COASTAL CAROLINAS...THERE IS SPREAD...PARTICULARLY OFFSHORE. THE ECMWF ENSEMBLE MEMBERS CONTINUE TO FAVOR A MORE NORTHERN SOLUTION RELATIVE TO THE GEFS/CMC MEMBERS. THE 12Z ECMWF MEMBERS HAVE SHOWN GREAT CONTINUITY TO THE PREVIOUS MODEL CYCLE WHICH SHOWS IT IS A FAIRLY STABLE SOLUTION. THE 00Z NAM SEEMS TO SUPPORT THIS IDEA AS WELL AS OTHER RECENT GUIDANCE LIKE THE 00Z CMC/UKMET. GIVEN THE ASSESSMENT HERE...WILL MAINTAIN THE PREVIOUS PREFERENCE AS THE 00Z NAM/ECMWF HAVE GARNERED ADDITIONAL SUPPORT. PLAN ON REMOVING THE 12Z ECMWF ENSEMBLE MEAN FROM THE MIX GIVEN THE REDUCTION IN SPREAD. ...BROAD WESTERN U.S. TROF THROUGHOUT THE PERIOD... FINAL PREFERENCE: BLEND OF THE 00Z ECMWF/12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE THE OTHER PERSISTENT FEATURE ON THE MAP HAS BEEN THE GENERAL UPPER TROF POSITIONED ACROSS THE WESTERN U.S. DURING THIS PERIOD...A SERIES OF SHORTWAVES WILL NAVIGATE THROUGH THE DESERT SOUTHWEST AND INTO THE ROCKIES/GREAT PLAINS REGION. THE LEAD SYSTEM CURRENTLY MOVING TOWARD THE CENTRAL PLAINS IS EXPECTED TO DAMPEN AND EVENTUALLY MERGE WITH THE NORTHERN STREAM. ON ITS WINGS...MODELS SHOW A MUCH MORE PRONOUNCED UPPER TROF DIGGING INTO SOUTHERN CA WITH ADDITIONAL SHORTWAVE ENERGY LIFTING NORTHEASTWARD IN ADVANCE. THERE IS GENERAL CLUSTERING WITH THE INITIAL SHORTWAVE MOVING UP THE ROCKIES REACHING EASTERN WY BY 23/0000Z. HOWEVER...THERE ARE MUCH LARGER DETAIL DIFFERENCES WITH THE SUBSEQUENT UPPER TROF AS IT WORKS ITS WAY TOWARD THE FOUR CORNERS REGION. BUILDING HEIGHTS DOWNSTREAM ALLOWS THE FLOW TO BECOME MORE MERIDIONAL IN NATURE ACROSS THE ROCKIES/HIGH PLAINS. A VARIETY OF SOLUTIONS ARE PORTRAYED AS A SERIES OF SHORTWAVES SWING TOWARD THE CENTRAL ROCKIES ON SATURDAY MORNING. CONSIDERING THE SPAGHETTI PLOTS IN THE PAST FOUR MODEL CYCLES...THE ECMWF ENSEMBLE MEMBERS ARE QUITE STABLE. WILL FOCUS THE PREFERENCES ON ITS CONSISTENCY BUT FEEL THE DETERMINISTIC RUN IS USEFUL AS WELL. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER