MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1213 PM EDT SUN APR 19 2015 VALID APR 19/1200 UTC THRU APR 23/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...CENTRAL AND EASTERN U.S... PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH 60 HOURS BLEND OF THE 06Z GEFS MEAN AND 00Z ECENS MEAN...AFTER 60 HOURS CONFIDENCE: AVERAGE MERGING OF THE CLOSED LOW OVER THE CENTRAL PLAINS WITH A DIGGING NORTHERN STREAM SHORTWAVE WILL PRODUCE A CONSOLIDATED BROAD SCALE TROUGH OVER THE EASTERN U.S. BY TUES WITH A LARGE CLOSED LOW JUST NORTH OF THE GREAT LAKES BY WED. THERE IS GENERALLY GOOD MASS FIELD AGREEMENT ON THE LARGER SCALE WITH THE EVOLUTION OF THE HEIGHT FALLS AND ALSO WITH HOW SURFACE LOW PRESSURE LIFTS NORTH THROUGH THE GREAT LAKES ON MON AND INTO ONTARIO BY TUES. MOST OF THE DIFFERENCES ARE LATE IN THE SHORT RANGE ON WED WITH WHERE THE LOW IS POSITIONED. WILL PREFER A GENERAL MODEL COMPROMISE THROUGH 60 HOURS...AND THEN LEAN TOWARD A BLEND OF THE GEFS MEAN AND ECENS MEAN THEREAFTER WHICH SHOW REASONABLY GOOD CLUSTERING. ...UPPER TROUGH/CLOSED LOW OFFSHORE CALIFORNIA... PREFERENCE: BLEND OF THE 12Z NAM/00Z UKMET AND 00Z ECMWF CONFIDENCE: AVERAGE A BROAD TROUGH AND WEAK CLOSED LOW OFFSHORE CA WILL SLOWLY DROP SOUTHEAST AND OFFSHORE SOUTHERN CA BY TUES. MEANWHILE...ADDITIONAL NORTHERN STREAM SHORTWAVE ENERGY DIGGING SOUTHEAST OFFSHORE THE PACIFIC NORTHWEST IS EXPECTED TO SEPARATE OUT AND DROP SOUTH DOWN THE WEST COAST AND MERGE WITH THE EXISTING UPPER LOW LEADING TO A DEEPER OVERALL TROUGH/CLOSED LOW FEATURE OFFSHORE SOUTHERN CA BY WED. THE 12Z GFS BECOMES A STRONG OUTLIER SOLUTION WITH THIS SYSTEM...WITH THE 12Z NAM/00Z ECMWF AND 00Z UKMET ALL FAVORING A SOMEWHAT WEAKER/BROADER CLOSED LOW. THE 00Z GEM AGREE WITH THIS SCENARIO...BUT DISPLACES ITS CLOSED LOW/TROUGH A BIT NORTHEAST OF THE MULTI-MODEL CONSENSUS BY WED. WILL FAVOR A BLEND OF THE 00Z ECMWF/00Z UKMET AND 12Z NAM AS THESE SOLUTIONS ARE RELATIVELY WELL CLUSTERED AND SUPPORTED BY THE LATEST GEFS MEAN AND ECENS MEAN. ...SHORTWAVE TROUGH/FRONT MOVING INTO THE PACIFIC NORTHWEST TUESDAY... PREFERENCE: BLEND OF THE 00Z ECMWF AND 00Z GEM CONFIDENCE: AVERAGE THE 00Z UKMET IS THE FASTEST AND WEAKEST SOLUTION WITH THE SHORTWAVE MOVING INTO THE PACIFIC NORTHWEST BY TUES...WITH THE 12Z NAM THE SLOWEST AND DEEPEST. THE 12Z GFS/00Z GEM AND 00Z ECMWF ARE CLUSTERED IN BETWEEN...WITH THE 12Z GFS OF THIS GROUP IS A TAD SLOWER. THE LATEST GEFS MEAN AND ECENS MEAN TEND TO SUPPORT A CONSENSUS OF THE 00Z GEM AND 00Z ECMWF A BIT MORE THAN THE DETERMINISTIC GFS...SO A BLEND OF THE ECMWF AND GEM WILL BE PREFERRED FOR NOW. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON