MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1231 PM EDT TUE APR 29 2014 VALID APR 29/1200 UTC THRU MAY 03/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ...OCCLUDED CYCLONE OVER THE MIDDLE MISSISSIPPI VALLEY... PREFERENCE: 25 PERCENT EACH GFS/GEFS MEAN/ECMWF/ECMWF ENSEMBLE MEAN CONFIDENCE: AVERAGE OTHER THAN THE NAM WHICH IS FASTER TO PROGRESS THE BASE OF THE UPPER LOW'S TROUGH OUT OF THE OHIO VALLEY WHICH INFLUENCES THE SURFACE LOW ACROSS NEW YORK...THE MODELS SHOW REASONABLY GOOD AGREEMENT WITH SUBTLE DETAIL DIFFERENCES TYPICAL OF HIGHLY-STRUCTURED AND COMPLEX SYSTEMS. GIVEN THIS COMPLEXITY AND ASSOCIATED DIFFICULTY IN RESOLVING THE DETAILS...RECOMMEND A MULTI-MODEL OR ENSEMBLE APPROACH. ONE SUGGESTION IS TO USE A COMBINATION OF THE LATEST GFS/ECMWF AND THEIR RESPECTIVE ENSEMBLE MEANS. ...FRONTAL SYSTEM ACROSS THE CAROLINAS... PREFERENCE: EQUAL BLEND GFS/ECMWF CONFIDENCE: ABOVE AVERAGE THE NAM IS NEARLY A FAST AND NORTHERN OUTLIER WITH THE NORTHWARD PROGRESSION OF THIS FRONTAL SYSTEM ACROSS THE MID-ATLANTIC/NORTHEAST/NEW ENGLAND. GIVEN TIGHT CLUSTERING FOR A SLOWER SOLUTION... RECOMMEND DISCOUNTING THE NAM IN FAVOR OF AN EQUAL BLEND OF THE GFS/ECMWF. THIS PREFERENCE INCLUDES THE WEAKER SURFACE LOW ACROSS NEW YORK ON THURSDAY ALSO DEPICTED BY THE NAM. ...SHORTWAVE TROUGH AFFECTING THE FOUR CORNERS REGION WEDNESDAY/THURSDAY... PREFERENCE: EQUAL BLEND GFS/ECMWF CONFIDENCE: ABOVE AVERAGE THE NAM LIES NEAR WEAK EDGES OF THE GUIDANCE WITH ITS MID LEVEL CENTER AND IS MORE PROGRESSIVE WITH ITS MOST NORTHERN PORTION EXITING INTO THE PLAINS. THEREFORE...RECOMMEND DISCOUNTING THE NAM IN FAVOR OF AN EQUAL BLEND OF THE GFS/ECMWF TO ADDRESS ANY LINGERING UNCERTAINTIES AND REMAINING SOLUTION SPREAD. ...COLD FRONT CROSSING THE NORTHERN HIGH PLAINS THURSDAY NIGHT/FRIDAY... PREFERENCE: EQUAL BLEND GFS/ECMWF CONFIDENCE: ABOVE AVERAGE THE NAM LIES NEAR THE SLOW EDGE OF THE GUIDANCE...WHILE THE OTHER SOLUTIONS...INCLUDING THE GFS/ECMWF SHOW MODESTLY CLOSE CLUSTERING FOR A FASTER SOLUTION. THEREFORE...RECOMMEND DISCOUNTING THE NAM IN FAVOR OF AN EQUAL BLEND OF THE GFS/ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... JAMES