MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1136 AM EST TUE NOV 24 2015 VALID NOV 24/1200 UTC THRU NOV 28/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO BE SUFFICIENTLY LARGE TO IMPACT THEIR FORECAST OF LARGE-SCALE FEATURES ...CLOSED LOW FORMING OVER THE NORTHWEST AND MOVING INTO THE GREAT BASIN... PRELIMINARY PREFERENCE: GFS/00Z ECMWF COMPROMISE CONFIDENCE: AVERAGE SPREAD AMONG THE MODELS IS LOW WITH RESPECT TO THIS FEATURE THROUGH 12-18Z WED. AFTER THIS TIME THE NAM BECOMES AN OUTLIER WHEN IT AMPLIFIED A SHORTWAVE MOVING AROUND THE EASTERN SIDE OF THE UPPER-LOW...EVEN CLOSING OFF ANOTHER UPPER-LEVEL LOW BY LATE THURSDAY OVER UT/ID/WY...WHILE THE STRONGER UPPER LOW FARTHER WEST RETROGRADES EVEN FARTHER WEST. THE GFS AND THE 00Z ECMWF SOLUTIONS APPEAR TO REPRESENT THE BEST CONSENSUS ENVELOPE AT THIS TIME...SO WILL PRELIMINARILY PREFER A COMPROMISE BETWEEN THESE TWO SOLUTIONS. ...UPPER TROUGH CROSSING SOUTHERN CANADA/NORTHERN PLAINS ON WED AND THURS... ...STRONG COLD FRONT PUSHING INTO THE MIDWEST AND SOUTHERN PLAINS... PREFERENCE: GENERAL MODEL COMPROMISE THROUGH 12Z THURS...00Z ECMWF AFTER 12Z THURS CONFIDENCE: ABOVE AVERAGE MODEL AGREEMENT IS RELATIVELY GOOD WITH RESPECT TO THE UPPER-LEVEL TROUGH THROUGH 12Z THURS...WITH THE NAM AND GFS BOTH LYING WITHIN THE CONSENSUS. AFTER THIS TIME THE GFS BECOMES A LITTLE FASTER WITH THE TROUGH RELATIVE TO THE NAM AND 00Z ECMWF/00Z ECMWF ENSEMBLE MEAN. THE GFS IS ALSO A LITTLE FAST COMPARED TO THE 06Z GEFS MEAN. THIS DIFFERENCE MANIFESTS IN THE SURFACE COLD FRONT CROSSING THE CENTRAL U.S. AS WELL...WITH THE GFS SHOWING A FASTER TIMING RELATIVE TO MOST OTHER GUIDANCE FROM THURSDAY MORNING ONWARD. THE NAM SOLUTION IS GENERALLY CLOSE TO THE 00Z ECMWF AND ITS ENSEMBLE MEAN...BUT IT DOES APPEAR TOO QUICK TO BUILD SHORTWAVE RIDGING INTO THE CENTRAL U.S. ON FRIDAY...WHICH CAUSES THE SURFACE FRONT TO SLOW AND BECOME FARTHER WEST OVER THE SOUTHERN PLAINS. THEREFORE...WILL RECOMMEND A GENERAL MODEL COMPROMISE THROUGH 12Z THURSDAY...AND THE 00Z ECMWF...WHICH SEEMS TO LIE IN THE MIDDLE OF CONSENSUS...AFTER THAT TIME. ...COLD FRONT CROSSING THE NORTHEAST ON FRIDAY... PREFERENCE: 00Z ECMWF/UKMET COMPROMISE CONFIDENCE: AVERAGE INCLUDING THE COLD FRONT CROSSING THE NORTHEAST ON FRIDAY IN A SEPARATE SECTION HERE AS THE PREFERENCE DIFFERS SOMEWHAT FROM THAT FOR THE SAME FRONT ACROSS THE PLAINS (WHICH BY FRIDAY WILL BE INFLUENCED BY THE UPPER-LEVEL OVER OVER THE WEST). SIMILARLY TO ACROSS THE PLAINS...THE GFS SOLUTION IS ON THE FAST SIDE OF THE SPREAD AS THE FRONT CROSSES THE NORTHEAST. THE NAM IS SLOWER AND MORE SIMILAR TO THE 00Z ECMWF AND UKMET. THE 00Z ECMWF ENSEMBLE MEAN IS EVEN A LITTLE SLOWER THAN THE 00Z DETERMINISTIC ECMWF. AT THIS TIME...PREFER A SOLUTION WITH TIMING REPRESENTED BY A COMPROMISE BETWEEN THE 00Z ECMWF/UKMET. ...BROAD AND SLOW MOVING UPPER LOW FORMING OVER THE BAHAMAS... PREFERENCE: NON-NAM COMPROMISE CONFIDENCE: AVERAGE MODELS ALL SIMILARLY CLOSE OFF A BROAD UPPER-LEVEL LOW OVER THE BAHAMAS ON THURSDAY. THE NAM EVENTUALLY ENDS UP FARTHER NORTH WITH THE LOW CENTER RELATIVE TO OTHER GUIDANCE. THUS...WILL RECOMMEND A NON-NAM COMPROMISE AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RYAN