MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 230 AM EDT TUE APR 14 2015 VALID APR 14/0000 UTC THRU APR 17/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM AND GFS EVALUATION INCLUDING THE UKMET/CANADIAN/ECMWF AND PREFERENCES ...LOW PRESSURE OVER THE TENNESSEE VALLEY... PREFERENCE: NAM CONFIDENCE: ABOVE AVERAGE COMPARISONS OF 00-06Z GUIDANCE TO OBSERVATIONS SHOW THE NAM TO HAVE AN EARLY LEAD WITH THE PLACEMENT AND DEPTH OF THE LOW TRACKING NORTHEASTWARD FROM THE MEMPHIS AREA...COMPARED WITH THE GFS/ECMWF AND OTHER SOLUTIONS. GIVEN ITS GOOD AGREEMENT WITH OBSERVATIONS AND ITS HIGHER RESOLUTION...RECOMMEND THE NAM ...UPPER LOW OVER WEST TEXAS... THE NEW ECMWF HAS TRENDED WEAKER AND FARTHER NORTH WITH THE LOW CENTER...AND NOW SHOWS GOOD AGREEMENT WITH OTHER GUIDANCE. ...SPLITTING UPPER TROUGH OVER THE WEST THROUGH THE PERIOD... PREFERENCE: 12Z ECMWF ENSEMBLE MEAN CONFIDENCE: BELOW AVERAGE A LOT OF SPREAD CONTINUES TO BE SHOWN BY THE VARIOUS ENSEMBLE MEMBERS WITH THE EVOLUTION OF THE TROUGH AS IT MOVES INLAND...AND WHILE THE NAM AND GFS AGREE OVERALL...DECREASING CONFIDENCE IS ASSOCIATED WITH THEIR FORECASTS FROM WEDNESDAY INTO THURSDAY. BY THURSDAY...THE MAIN DIFFERENCES CONCERN IF AND HOW THE DEVELOPING UPPER LOW CENTER WILL REMAIN INTACT OR SPLIT ONCE AGAIN...WITH THE NAM/GFS SUGGESTING A GREATER CHANCE OF LOW SEPARATING COMPARED WITH THE UKMET/CANADIAN/ECMWF...WHICH ARE MORE CONSOLIDATED OVER THE S. ROCKIES. GIVEN THESE UNCERTAINTIES...THE SPREAD...AND DISTANCE FROM SHORE RESULTING IN MINIMAL SAMPLING OF THE TROUGH...RECOMMEND AN INTERMEDIATE SOLUTION THAT IS BEST REPRESENTED BY THE 12Z ECMWF ENSEMBLE MEAN. ...LOW PRESSURE POSSIBLY FORMING ALONG THE SC/NC COAST THU-FRI... PREFERENCE: GFS CONFIDENCE: BELOW AVERAGE WHETHER A LOW FORMS OR NOT WILL LARGELY DEPEND ON THE AMOUNT AND LOCATION OF CONVECTION ORIGINATING OVER THE GULF DUE TO PERTURBATIONS EMBEDDED IN THE PERSISTENT SOUTHWESTERLY FLOW ALOFT OVER THE NEXT COUPLE DAYS. MOST SOLUTIONS SHOW VARIOUS FORMS OF CONVECTIVE GRID-SCALE FEEDBACK. THUS...CONFIDENCE IN ANY PARTICULAR SOLUTION IS QUITE LOW. HOWEVER...HAVING A LOW ALONG THE COAST IN VICINITY OF THE RESIDUAL FRONTAL BOUNDARY IS QUITE REASONABLE. THE NEW ECMWF IS WEAKER THAN THE GFS AND ALSO QUITE POSSIBLE...WHILE THE NAM/CANADIAN ARE THE STRONGEST AND FARTHEST NORTH...THUS CONSIDERED MOST UNLIKELY AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES