697  
FXUS10 KWNH 180629  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
228 AM EDT WED OCT 18 2017  
 
VALID OCT 18/0000 UTC THRU OCT 21/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
...UPPER TROUGH DIGGING INTO THE PACIFIC NORTHWEST WEDNESDAY NIGHT  
WITH ASSOCIATED ATMOSPHERIC RIVER EVENT...  
LEADING SHORTWAVE MOVING FROM THE SOUTHWEST INTO THE PLAINS  
BROAD UPPER TROUGH/COLD FRONT REACHING THE PLAINS FRIDAY/SATURDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NAM/GFS/ECMWF BLEND; CONFIDENCE ABOVE AVERAGE  
 
DIFFERENCES IN THE GUIDANCE SHOWS UP AFTER THE UPPER TROUGH AXIS  
MOVES OVER THE INTERMOUNTAIN WEST ON FRIDAY. THE 12Z CANADIAN IS  
THE FASTEST WITH THIS SYSTEM WHILE THE 12Z UKMET IS THE SLOWEST.  
WHILE THE SYSTEM IS EMBEDDED WITHIN A QUASI-ZONAL FLOW REGIME --  
WHICH COULD SUPPORT A FASTER SOLUTION -- THE CANADIAN ISSUES  
APPEAR TO STEM FROM AN UPSTREAM DEEP CYCLONE SOUTH OF AK WHICH IS  
HANDLES DIFFERENTLY THAN THE OTHER GUIDANCE. THE 00Z NAM/00Z  
GFS/12Z ECMWF FORM AN INTERMEDIATE COMPROMISE WHICH IS MOST  
AGREEABLE WITH THE 12Z ECMWF/18Z GEFS MEAN SOLUTIONS.  
 
DEEP CYCLONE MOVING THROUGH SOUTHERN/EASTERN CANADA  
TRAILING COLD FRONT MOVING THROUGH THE NORTHERN U.S. WED-THU  
TROUGH MOVING OUT OF THE SOUTHEAST WEDNESDAY/THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS SYSTEM. A COMPROMISE  
OF THE 12Z UKMET, 12Z ECMWF, 12Z CANADIAN, 00Z NAM, AND 00Z GFS IS  
PREFERRED 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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