477  
FXUS10 KWNH 091831  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 PM EST SAT DEC 09 2017  
 
VALID DEC 09/1200 UTC THRU DEC 13/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL PREFERENCES AND CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
ERRORS WITHIN THE GFS/NAM INITIALIZATIONS DO NOT SEEM TO DEGRADE  
THEIR SHORT RANGE FORECASTS.  
 
 
SYSTEM SIDESWIPING THE PACIFIC NORTHWEST MONDAY AFTERNOON  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: ECMWF/UKMET/CANADIAN BLEND; CONFIDENCE AVERAGE  
 
THE 12Z GFS/TO SOME DEGREE THE 12Z NAM WAS QUICKER THAN THE OTHER  
GUIDANCE MOVING THIS SYSTEM THROUGH WESTERN CANADA INTO ALBERTA BY  
LATE TUESDAY. THE 00Z ECMWF/ITS ENSEMBLE MEAN LOOK TOO  
STRONG/SLOW WITH THE SYSTEM THEY MAINTAIN AS A CLOSED LOW MOVING  
OVER THE TOP OF THE RIDGE -- IT SHOULD END UP WEAKER DUE TO THE  
SUPERGEOSTROPHIC FLOW IN THE REGION. IT SHOULD PROBABLY MOVE ON A  
MORE NORTHERLY TRAJECTORY AS WELL BASED ON THE POSITION OF THE  
NORTHERNMOST EXTENT OF THE RIDGE NORTH OF AK. A COMPROMISE OF THE  
12Z ECMWF, 12Z UKMET, AND 12Z CANADIAN IS PREFERRED TO TAKE CARE  
OF THE ECMWF ISSUE WITH AVERAGE CONFIDENCE.  
 
UPPER LOW PARKING ACROSS NORTHWEST MEXICO MONDAY ONWARD  
SECOND STRONGER CLIPPER MOVING ACROSS GREAT LAKES MON/TUE  
CLIPPER DIVING INTO THE UPPER MIDWEST SUNDAY  
SYSTEM MOVING BY THE NORTHEAST TODAY/SUNDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE SYSTEMS. A  
COMPROMISE OF THE 12Z GFS, 12Z NAM, 12Z ECMWF, 12Z UKMET, AND 12Z  
CANADIAN IS PREFERRED TO DEAL WITH LINGERING DETAIL ISSUES WITH  
ABOVE AVERAGE CONFIDENCE.  
 
THE NEXT COMPLETE MODEL DIAGNOSTIC DISCUSSION (PMDHMD) WILL BE  
ISSUED BY 1645Z SUNDAY.  
 
ROTH  
 
PREVIOUS MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
PREVIOUS 500 MB FORECASTS AT  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 

 

 
 
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