MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1254 AM EDT WED APR 29 2015 VALID APR 29/0000 UTC THRU MAY 02/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...00Z NAM/GFS EVALUATION... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...DE-AMPLIFYING UPPER LOW MOVING ACROSS THE LOWER MS VALLEY/SOUTHEAST WED... ...SURFACE LOW OVER THE NORTHERN GULF OF MEX... CONFIDENCE: GENERAL MODEL COMPROMISE PREFERENCE: ABOVE AVERAGE LATEST OPERATIONAL MODEL RUNS SHOW GOOD AGREEMENT. ...UPPER LOW DROPPING THROUGH THE UPPER GREAT LAKES EARLY INTO THE OH VALLEY THU..ROTATING ACROSS THE MID ATLANTIC ON FRI... ...SURFACE LOW DEEPENING ALONG THE MID ATLANTIC COAST THU-FRI... CONFIDENCE: GFS/NAM PREFERENCE: AVERAGE THE MODELS APPEAR TO BE SETTLING A SOLUTION WITH BOTH THE 00Z NAM/GFS SHOWING FAIRLY GOOD RUN-TO-RUN CONTINUITY WITH THE THEIR 12Z RUNS. MODEL SPREAD APPEARS TO BE DECREASING AS WELL WITH THE NAM AND GFS SHOWING BETTER AGREEMENT...ESPECIALLY AT 500 MB. AT THE SURFACE...THE NAM LOW TRACK MOVES WEST OF THE GFS AS THE SYSTEM MOVES OFF OF THE MID ATLANTIC COAST...BUT OVERALL DIFFERENCES ARE RELATIVELY MINOR. STILL SOME UNCERTAINTY REMAINS HOWEVER...AS BOTH NCEP MODELS BECOME SLOWER/DEEPER ALOFT THAN THE 12Z ECMWF AS THE UPPER LOW MOVES ACROSS THE MID ATLANTIC EARLY FRI. AS A RESULT...BEGINNING LATE FRI...THE ECMWF TRACKS IT SURFACE LOW WELL EAST OF THE THE NCEP MODELS. THE 00Z UKMET SUPPORTS A SLOWER/MORE AMPLIFIED SOLUTION ALOFT AND WHILE NOT AS SLOW/AMPLIFIED AS THE NCEP MODELS...THE 12Z EC ENSMEAN WAS SLOWER THAN THE OPERATIONAL ECMWF. ...UPPER LEVEL SHORTWAVE TROUGH/SURFACE FRONT MOVING FROM THE PACIFIC NORTHWEST TO THE NORTHERN PLAINS WED-FRI... CONFIDENCE: NAM/GFS/12Z ECMWF PREFERENCE: AVERAGE OVERALL THE MODELS ARE IN GOOD AGREEMENT WITH ONE ANOTHER. AN EXCEPTION IS THE 00Z UKMET...WHICH FOR A PERIOD IS SLOWER THAN THE 00Z NAM/GFS AND 12Z ECMWF WITH THE UPPER TROUGH AND SURFACE FRONT AS IT MOVES ACROSS THE NORTHERN PLAINS LATE THU-FRI. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... PEREIRA