MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 236 PM EDT THU MAY 21 2015 VALID MAY 21/1200 UTC THRU MAY 25/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GFS/NAM INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. SOUTHWEST U.S. TROF LIFTING INTO FRONT RANGE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FINAL PREFERENCE: BLEND 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN CONFIDENCE: AVERAGE MODELS AGREE THAT A BROAD LOW OVER WEST COAST WILL DIG CENTERING OVER LAS VEGAS BY EARLY SATURDAY. SOLUTIONS BEGIN TO DIVERGE IN TIMING AND STRENGTH WITH THE EJECTION TO THE PLAINS... PARTICULARLY IN THE SURFACE PATTERN. THE NCEP MODELS HAVE BEEN TENDING TO DEVELOP A MORE AGGRESSIVE AND FASTER SURFACE LOW IN NORTHEASTERN COLORADO WITH INVERTED SURFACE TROF ACROSS THE NORTHERN PLAINS WHILE THE 00Z ECMWF TENDS TO HOLD BACK THE ENERGY IN THE BASE...CURRENT PREFERENCE IS TIED TO THE ECWMF WITH ITS BETTER RUN TO RUN CONSISTENCY. THE 12Z NAM APPEARS TO BE GETTING IN BETTER AGREEMENT WITH A VIABLE SURFACE SOLUTION BY END OF THE PERIOD BUT WAS A BIT INCONSISTENT WITH THE INITIAL EJECTING SHORTWAVE WITH A DEEPER FURTHER NORTH SOLUTION. THE 12Z GFS CONTINUES TO BE CONSISTENT WITH ITS PRIOR RUNS AND LOOKS REASONABLE UP TO DAY TWO. THE 12Z ECMWF HAS TRENDED TOWARD THE EAST SLIGHTLY AND COMES INTO BETTER AGREEMENT WITH THE SUITE OF MODEL GUIDANCE PARTICULARLY THE 00Z ECMWF ENSEMBLE MEAN. LOOSELY DEFINED TROF OVER NORTHWEST U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FINAL PREFERENCE: BLEND OF 12Z ECMWF/00Z ECMWF ENSEMBLE MEAN CONFIDENCE: BELOW AVERAGE LARGE MODEL AND ENSEMBLE SOLUTION SPREAD EXISTS WITH A LOOSELY DEFINED TROF ACROSS COASTAL BRITISH COLUMBIA. THE EVOLUTION OF THIS FEATURE IS HIGHLY TIED TO THE UPSTREAM TROF DEVELOPING OVER THE GULF OF ALASKA. THE GFS/GEFS MEAN CONTINUE TO BE STRONGEST/FASTEST TO PULL ENERGY SOUTHWARD INTO OREGON AND CALIFORNIA BY THE END OF THE PERIOD...WHILE ECMWF SOLUTIONS HAVE BEEN LESS AGGRESSIVE...INFLUENCED BY THE SLOWER BUT ALSO MORE CONSISTENT RUN TO RUN UPSTREAM EVOLUTION. THE ECMWF EVENTUALLY KICKS THE TROF SOUTHWARD BY DAY 3 WHICH IS IN AGREEMENT WITH WPC MEDIUM-RANGE DISCUSSION...PMDEPD. GIVEN HIGH SPREAD CONFIDENCE IS QUITE LOW. SYSTEMS MOVING THROUGH THE NORTHEAST/MID-ATLANTIC ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FINAL PREFERENCE: BLEND OF GENERAL MODEL GUIDANCE CONFIDENCE: ABOVE AVERAGE LEADING WEAK SHORTWAVE ACROSS THE EASTERN GREAT LAKES ALONG WITH DEEPENING LARGE SCALE TROF ACROSS JAMES BAY INTO QUEBEC CONTINUE TO FOLLOW MODEL TRENDS AND REMAIN IN EXCELLENT AGREEMENT. THE SURFACE REFLECTIONS IN THE CAROLINA/COASTAL ATLANTIC AS WELL AS THE NEW ENGLAND LOW AND COLD FRONT ALSO SHOWS GOOD AGREEMENT BEFORE EXITING THE U.S. BY MIDDAY SATURDAY. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA/BURKE