MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 256 PM EDT FRI APR 17 2015 VALID APR 17/1200 UTC THRU APR 21/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NOTE THAT THE 17/12Z CMC WAS NOT AVAILALBE FOR THIS DISCUSSION. NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. UPPER LOW CLOSING OFF IN NORTHERN MN EARLY MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/00Z ECMWF COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z GFS IS FASTER WITH THE UPPER TROUGH REACHING THE NRN PLAINS BY SUN MORNING...WITH THE 12Z UKMET SLOWEST/BACK TOWARD THE WEST. THE ENSEMBLE MEANS SUPPORT A MIDDLE GROUND...CLOSEST TO THE 12Z NAM AND 00Z ECMWF WHICH FIT THE MIDDLE OF THE DETERMINISTIC SPREAD. THE 12Z ECMWF MADE SOME SMALL AJUSTMENTS TO BE WEAKER ALOFT AND NOW DIGS THE SHORTWAVE ENERGY A BIT FARTHER SOUTH THAN ITS PREVIOUS CYCLE. THE 00Z ECMWF IS CONSIDERED A BETTER CYCLE THAN THE 12Z ECMWF. CLOSED LOW WEAKENING EWD FROM THE ROCKIES SURFACE LOW REACHING THE GREAT LAKES REGION SUN NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS/ECMWF/UKMET COMPROMISE CONFIDENCE: AVERAGE THE 12Z ECMWF/UKMET MADE ADJUSTMENTS TOWARD THE 12Z NAM/GFS AND NOW ONLY THE 00Z CMC APPEARS SIGNIFICANTLY DIFFERENT WITH THE EVOLUTION OF THE CLOSED LOW FROM THE WEST AND SHOTWAVE ORIGINATING FROM NRN MEXICO. ENSEMBLE SCATTER LOW PLOTS SUPPORT A NAM/GFS/ECMWF/UKMET POSITION WITH A BLEND IN POSITION/STRENGTH CLOSLY MATCHING THE ENSEMBLE MEANS. *ENERGY ALOFT DROPPING DOWN THE CA COAST SAT/SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z CMC COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE GUIDANCE SHOWS REASONABLY GOOD AGREEMENT WITH THIS SYSTEM OUTSIDE OF THE 00Z CMC WHICH IS FARTHER OFFSHORE. A BLEND IN STRENGTH OF THE NON 00Z CMC IS PREFERRED. SHORTWAVE CROSSING NEW ENGLAND SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM / 12Z ECMWF BLEND CONFIDENCE: ABOVE AVERAGE THE 12Z GFS TRENDED MUCH WEAKER ALOFT AND HAS AN ILL DEFINED SURFACE LOW NEAR MAINE...WHILE THE SREF/GEFS/EC MEANS SUPPORT MORE OF A LOW LEVEL REFLECTION FROM THE UPPER WAVE THAN THE GFS DEPICTS. THE 12Z UKMET IS WEAK...SIMILAR TO THE 12Z GFS AND WEAK COMPARED TO THE ENSEMBLE MEANS...BUT THE 12Z NAM AND 12Z ECMWF MAKE UP A GOOD COMPROMISE IN LINE WITH THE AGREEABLE ENSEMBLE MEANS. GIVEN THE SHORT TERM NATURE OF THIS FEATURE AND THE GOOD AGREEMENT SEEN IN THE ENSEMBLES...CONFIDENCE IS ABOVE AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO