MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 335 AM EDT FRI MAY 15 2015 VALID MAY 15/0000 UTC THRU MAY 18/1200 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. ...INITIAL SHORTWAVE MOVING FROM THE UPPER GREAT LAKES TOWARD NEW ENGLAND... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE A BROAD SHORTWAVE CURRENTLY MOVING TOWARD THE UPPER PENINSULA OF MI IS SPREADING A BROAD AXIS OF LIGHT RAINFALL TO THE UPPER GREAT LAKES REGION. THE PARENT SHORTWAVE WILL GRADUALLY SHEAR WHILE MOVING TOWARD NEW ENGLAND ON SATURDAY MORNING. THE MODELS ARE IN CLOSE ENOUGH AGREEMENT TO SUPPORT A GENERAL MODEL COMPROMISE. ...UPPER TROF SKIRTING NORTHERN NEW ENGLAND BY 17/1200Z... ...SURFACE LOW MOVING OFF THE COAST... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE MODELS SHOW A NORTHERN STREAM TROF GRAZING THE UPPER SECTIONS OF NEW ENGLAND BY SUNDAY MORNING. OVERALL THE GUIDANCE CLUSTER QUITE WELL WITH THE AMPLITUDE OF THIS FEATURE WITH SOME VARIABILITY IN THE SURFACE PATTERN. A GENERAL MODEL COMPROMISE APPEARS WARRANTED HERE. ...BROAD/ANOMALOUS CLOSED LOW EJECTING OUT OF THE SOUTHWESTERN U.S... ...SURFACE CYCLONE TRACKING ALONG THE NORTHERN TIER... FINAL PREFERENCE: BLEND OF THE 00Z GFS/ECMWF WITH THE 00Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: AVERAGE A FULL-LATITUDE UPPER TROF INITIALLY ANCHORING THE WESTERN HALF OF THE COUNTRY WILL TRANSLATE EASTWARD IN TIME CARRYING STRONG HEIGHT FALLS TOWARD THE PLAINS. THE 00Z CMC SEEMS TO HAVE ADJUSTED ITS PREVIOUS SOLUTION TRENDING A BIT SLOWER BRINGING IT BACK TOWARD THE STRONG MODEL CLUSTERING. DURING THE WEEKEND...THE MODELS SHOW SOME DIFFERENCES REGARDING THE PRECISE LOCATION OF THE UPPER LOW. THE 00Z CMC/ECMWF/UKMET ARE POSITIONED SOUTH OF WHERE THE ENSEMBLES CLUSTER ACROSS THE NORTHERN/CENTRAL PLAINS ON SUNDAY MORNING. LOOKING AT THE SURFACE...THE MODELS ARE RATHER CLOSE THROUGH 18/0000Z WITH THE EXCEPTION OF THE 00Z NAM/CMC WHICH ARE OFF TO THE SOUTHWEST WITH THEIR POSITION. OVERALL...THE 00Z ECMWF SEEMS TO HAVE IMPROVED ENOUGH UPON ITS PREVIOUS SOLUTION TO SUPPORT ITS INCLUSION INTO THE PREFERENCE. WILL RECOMMEND A 00Z GFS/ECMWF BLEND WITH THE ENSEMBLE MEANS TO ACCOUNT FOR UNCERTAINTY. ...NEXT UPPER TROF AFFECTING THE WESTERN U.S. BY SUNDAY/MONDAY... FINAL PREFERENCE: MODEL COMPROMISE BETWEEN THE 00Z NAM/GFS/ECMWF FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE TOWARD THE END OF THE PERIOD...ANOTHER BROAD UPPER TROF IS FORECAST TO APPROACH THE SOUTHWESTERN U.S. THE 00Z NAM/GFS/ECMWF ARE IN FAIRLY GOOD AGREEMENT WITH THIS FEATURE AND ARE SUPPORTED BY THE ENSEMBLE MEANS. WILL UTILIZE A COMPROMISE OF THESE SOLUTIONS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER