160  
FXUS10 KWNH 120435  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1234 AM EDT THU OCT 12 2017  
 
VALID OCT 12/0000 UTC THRU OCT 15/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
SYSTEM MOVING FROM THE PACIFIC NW INTO THE UPPER MIDWEST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NAM/CANADIAN/ECMWF COMPROMISE; CONFIDENCE AVE  
 
STARTING SATURDAY MORNING, DIFFERENCES EMERGE WITH THIS SYSTEM.  
THE 00Z GFS IS STRONGER AND THEN QUICKER/MORE CLOSED ALOFT WITH  
THIS SYSTEM -- FROM SATURDAY AFTERNOON ONWARD CONVECTIVE/GRIDSCALE  
FEEDBACK TAKES HOLD SO IT'S LIKELY TOO STRONG ALOFT AND TOO QUICK  
WITH THIS SYSTEM, WHICH IS ALSO BORNE OUT BY THE 12Z GLOBAL  
ENSEMBLE ENVELOPE WHICH ITS SURFACE LOW LIES OUTSIDE OF. THE 12Z  
UKMET SHOWS THE MOST POSITIVELY TILTED SYSTEM/FLATTEST WAVE WHICH  
ONE WOULD THINK WOULD HAVE LESS TILT ALOFT BECAUSE OF BROAD  
RIDGING UPSTREAM. THE 12Z UKMET SURFACE SOLUTION IS ALSO OUTSIDE  
THE 12Z GLOBAL ENSEMBLE ENVELOPE, SO IT WAS CONSIDERED A LOW  
PROBABILITY ALTERNATIVE SCENARIO. A COMPROMISE OF THE 00Z NAM,  
12Z CANADIAN, AND 12Z ECMWF DEFINES THE BORDERS OF THE BEST GLOBAL  
ENSEMBLE CLUSTERING, SO A COMPROMISE OF THESE SOLUTIONS IS  
PREFERRED WITH AVERAGE CONFIDENCE.  
 
SYSTEM MOVING THROUGH THE NORTHEAST THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CANADIAN BLEND; CONFIDENCE ABOVE AVERAGE  
 
THE 12Z CANADIAN IS INCREASINGLY WEAKER/SOMEWHAT QUICKER THAN THE  
REST OF THE GUIDANCE WITH THIS SYSTEM. WHILE IT IS EXPECTED TO  
SHEAR OUT WITHIN A QUASI-ZONAL FLOW REGIME, EVEN THE 18Z GEFS  
MEAN/12Z ECMWF ENSEMBLE MEAN SHOW GREATER AMPLITUDE. A COMPROMISE  
OF THE 12Z UKMET, 12Z ECMWF, 00Z NAM, AND 00Z GFS IS PREFERRED  
WITH ABOVE AVERAGE CONFIDENCE.  
 
FRONT MOVING INTO THE GREAT LAKES/NORTHEAST FRIDAY/SATURDAY  
TROPICAL WAVE/UPPER LOW MOVING THROUGH THE FL STRAITS FRIDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE SYSTEMS. PREFER A  
COMPROMISE OF THE 12Z ECMWF, 12Z CANADIAN, 12Z UKMET, 00Z NAM, AND  
00Z GFS TO IRON OUT ANY LINGERING DETAIL ISSUES WITH ABOVE AVERAGE  
CONFIDENCE.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ROTH  

 
 
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