MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1153 PM EST WED NOV 23 2016 VALID NOV 24/0000 UTC THRU NOV 27/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... ...PROGRESSIVE SHORTWAVE MOVING FROM THE LOWER OH VALLEY INTO NEW ENGLAND... PRELIMINARY PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: ABOVE AVERAGE A GRADUALLY WEAKENING TROUGH SEEN ON WATER VAPOR IMAGERY TRAVERSING THROUGH THE OH/TN VALLEYS WILL MIGRATE NORTHEASTWARD DURING THE NEXT DAY OR SO. LIGHT TO MODERATE RAINFALL CONTINUES TO FALL ALONG THE ATTENDANT COLD FRONT WITH THE SYSTEM EXITING OFF THE EASTERN SEABOARD BY THANKSGIVING NIGHT. ANY DIFFERENCES DO NOT SEEM TO BE TOO IMPACTFUL ON THE FORECAST WHICH WOULD SUPPORT A GENERAL MODEL COMPROMISE HERE. ...SYSTEM TRACKING FROM THE CENTRAL GREAT BASIN TOWARD THE GREAT PLAINS... ...EVENTUAL LONGWAVE TROUGH EXTENDING OVER THE NORTHEASTERN U.S. BY THIS WEEKEND... ...AREA OF SURFACE CYCLOGENESIS OFF OF THE NEW ENGLAND COAST... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE WITHIN THE LOW AMPLITUDE FLOW REGIME ACROSS THE CONUS...A MODEST BAND OF HEIGHT FALLS CURRENTLY EXITING THE CENTRAL GREAT BASIN WILL CONTINUE TO MARCH EASTWARD REACHING THE UPPER GREAT LAKES BY 25/1200Z. AT THIS POINT THERE WILL BE SOME INTERACTION WITH THE NORTHERN STREAM WHICH SHOULD AID IN THE DEVELOPMENT OF A MORE PRONOUNCED UPPER TROUGH ACROSS THE NORTHEAST LATE IN THE PERIOD. IT APPEARS THE 00Z NAM/GFS ARE ON THE MORE PROGRESSIVE SIDE OF THE MODEL SPREAD WHILE THE 12Z ECMWF/UKMET CLUSTER BACK TO THE WEST A BIT. THE 00Z NAM BECOMES PARTICULARLY QUICK MOVING INTO THE DAY 3 REALM SO WILL DISCOUNT ITS SOLUTION AS AN OUTLIER AT THAT POINT. THE MEAN TROUGHING OVER THE NORTHEASTERN U.S. IS FORECAST TO ULTIMATELY DEVELOP A WAVE OF LOW PRESSURE OFF OF NEW ENGLAND WITH MANY SOLUTIONS FAVORING MORE THAN ONE WAVE. ENSEMBLE LOW PLOTS STILL SHOW QUITE A BIT OF SPREAD OVER THE REGION WITH MOST OF THE 12Z ECMWF MEMBERS TO THE NORTH OF THE GEFS/CMC SOLUTIONS. UNTIL FURTHER GUIDANCE ARRIVES...WPC WILL TAKE A SPLIT BETWEEN THE QUICKER 00Z GFS AND SLOWER 12Z ECMWF. ...INITIAL UPPER LOW ACROSS THE NORTHEASTERN PACIFIC... ...ASSOCIATED SHORTWAVE MOVING INTO COASTAL WA BY 25/0600Z... PRELIMINARY PREFERENCE: MODEL CONSENSUS BETWEEN THE 00Z NAM/GFS AND 12Z ECMWF FORECAST CONFIDENCE: ABOVE AVERAGE DEEP CYCLONIC FLOW ACROSS THE NORTHEASTERN PACIFIC WILL MAINTAIN A CORRIDOR OF LOWER HEIGHTS OVER THE REGION. ONE EMBEDDED SHORTWAVE WILL TAKE AIM AT THE WA COASTLINE BY 25/0600Z. SUBTLE DIFFERENCES ARE EVIDENT AS THIS OCCUR WITH THE 12Z UKMET A HAIR QUICKER OF THE CONSENSUS WHILE THE 12Z CMC LAG TO THE WEST. ULTIMATELY WILL FAVOR THE CONSENSUS OF THE 00Z NAM/GFS WITH THE 12Z ECMWF. ...SHARP BAND OF HEIGHT FALLS PUSHING THROUGH SOUTHERN/CENTRAL CA BY SATURDAY AFTERNOON... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE WITHIN THE MEAN UPPER TROUGH ANCHORING THE EASTERN PACIFIC...A SHARPENED AXIS OF LOWER HEIGHTS WILL WORK THEIR WAY TOWARD THE SOUTHERN/CENTRAL CA COAST EARLY THIS WEEKEND. COMPARING THE PAST FOUR SPAGHETTI PLOTS DATING TO 36 HOURS AGO...THERE IS A DECIDED SLOWING TREND...PARTICULARLY AMONG THE ECMWF ENSEMBLE MEMBERS. THE 00Z GFS ALSO MADE AN ADJUSTMENT WESTWARD RELATIVE TO THE 18Z CYCLE. THE 00Z NAM IS PERHAPS TOO FAR WEST BUT SHOULD NOT BE COMPLETELY DISCOUNTED GIVEN THE RECENT TRENDS IN THE GUIDANCE. MEANWHILE...THE 12Z CMC IS OFF TO THE RACES EARLY ON AND CONTINUES THAT IDEA THROUGHOUT THE SHORT RANGE PERIOD. A COMBINATION OF THE 00Z GFS/12Z ECMWF WOULD BE A GOOD STARTING POINT ALTHOUGH MAY MAKE SOME TWEAKS BASED ON ADDITIONAL GUIDANCE IN THE NEXT ISSUANCE. ...SECONDARY AXIS OF SHORTWAVE ENERGY TRAILING THE INITIAL SURGE INTO THE DESERT SOUTHWEST... PRELIMINARY PREFERENCE: BLEND OF THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: AVERAGE ON THE HEELS OF THE INITIAL SHORTWAVE PUSHING INTO THE DESERT SOUTHWEST...A SECONDARY BAND OF HEIGHT FALLS WORK THEIR WAY SOUTHWARD TOWARD THE CA COAST DURING THE WEEKEND. ONE SOLUTION WHICH IS COMPLETELY OUT OF THE PHASE IS THE 21Z SREF MEAN WHICH IS WELL TO THE EAST. ENSEMBLE SPAGHETTI PLOTS INDICATE THE GEFS MEMBERS ARE CLUSTERING WEST OF THE ECMWF ENSEMBLES. THE LATTER SEEMS TO HAVE SUPPORT FROM THE 12Z UKMET WHILE THE FORMER HAS THE 00Z NAM IN ITS CAMP. EITHER SCENARIO APPEARS PLAUSIBLE SO WILL TAKE A SPLIT BETWEEN THEIR TWO ENSEMBLE MEANS GIVEN THE UNCERTAINTY IN PLAY. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER