MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1157 AM EST THU NOV 20 2014 VALID NOV 20/1200 UTC THRU NOV 24/0000 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 SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...STRONG SOUTHERN STREAM TROUGH LEADING TO WIDESPREAD RAIN FROM THE PLAINS EASTWARD... PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF A DYNAMIC TROUGH OF SHORT TO MEDIUM WAVELENGTH WILL DIVE FROM CALIFORNIA TOWARD THE RIO GRANDE BASIN. THE SYSTEM WILL CONTINUE TO BE URGED ALONG TO THE EAST BY STRONG UPSTREAM FLOW...BUT THE NAM/GFS HAVE TRENDED TOWARD A SLOWER PROGRESSION FROM LATE SATURDAY INTO SUNDAY. THEY ARE ALSO A LITTLE DEEPER AND HAVE THE TRACK SUPPRESSED SOUTHWARD COMPARED TO THE 00Z ECMWF. THESE TRENDS APPEAR REASONABLE FOR A STRONG AND STILL DEEPENING WAVE. WHEN COMBINED WITH THE 00Z UKMET/CANADIAN SOLUTIONS...THE 12Z RUNS START TO MAKE THE ECMWF LOOK LIKE MORE OF AN OUTLIER...SO WE WOULD EXPECT A GOOD CHANCE OF SEEING SIMILAR TRENDS IN THE NEW ECMWF RUN WHEN IT ARRIVES. THE NAM IS WITHHELD FROM OUR PREFERENCE BECAUSE IT IS LESS PREFERRED BY THE QPF DESKS...BUT ITS MASS FIELD SOLUTION COULD BE USEFUL. ...NORTHERN STREAM TROUGH AFFECTING THE NORTHWEST/ROCKIES/NORTHERN PLAINS... PREFERENCE: BLEND OF 12Z NAM/GFS THE NAM AND GFS TRENDED SLIGHTLY FASTER WITHIN THE NORTHERN STREAM FLOW AFFECTING STATES FROM WA/OR EASTWARD TO THE DAKOTAS. NAM/GFS TRENDS IN THE SOUTHERN STREAM APPEARED REASONABLE. STRONG WESTERLY FLOW IN THE NORTHERN STREAM...ALONG WITH THE GEFS MEAN AND 00Z UKMET/CANADIAN SOLUTIONS LEND SUPPORT TO THE NOTION OF A SLIGHTLY FASTER SYSTEM. THE OLDER ECMWF AND ECMWF ENSEMBLE MEAN HAD SUGGESTED SOMETHING A LITTLE SLOWER. THE GFS MAY ERR A BIT TOO FAR ON THE FAST SIDE...WHICH WOULD BE CONSISTENT WITH ITS BIAS...BUT ALL OF THIS SEEMS TO HAVE LESS OF AN IMPACT TO THE LOW LEVEL OR SURFACE FORECAST. FOR NOW WE WILL SIDE WITH THE CONSENSUS AND THE TRENDS. ...PHASING RESULTING IN A DEEP CYCLONE OVER THE MIDWEST AND GREAT LAKES BY SUN/MON... PREFERENCE: BLEND OF 12Z NAM/GFS STREAM PHASING IS FORECAST TO YIELD THE BEGINNINGS OF A VERY DEEP MIDWESTERN U.S. CYCLONE BY SUNDAY. OVER SEVERAL MODEL CYCLES THE ENSEMBLE MEANS HAVE BEEN CONSISTENT IN THE PLACEMENT AND INTENSITY OF THE SURFACE LOW. EVEN WITH THE SLIGHT MID LEVEL VARIATION IN THE OPERATIONAL MODELS THEIR SURFACE FORECASTS HAVE NOT CHANGED VERY DRAMATICALLY FROM RUN TO RUN. THE 12Z NAM/GFS SEEM TO CAPTURE THE TRENDS...AND ARE PREFERRED...ALTHOUGH THE NAM IS LIKELY NOT QUITE DEEP ENOUGH WITH THE SURFACE LOW...WHICH MOST GUIDANCE HAS DROPPING BELOW 990 MB BY 24/00Z. ...NORTHEASTERN U.S... PREFERENCE: ANY OF THE OPERATIONAL MODELS A SHORTWAVE TROUGH WILL SWING THROUGH NEW ENGLAND BY FRIDAY...FOLLOWED BY WARM ADVECTION AND A TRANSITION TOWARD MILD AIR AND SOUTHWESTERLY FLOW ALOFT. THE MODELS HANDLE THIS SIMILARLY. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE