368  
FXUS10 KWNH 081623  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1122 AM EST FRI DEC 08 2017  
 
VALID DEC 08/1200 UTC THRU DEC 12/0000 UTC  
 
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
ERRORS WITHIN THE GFS/NAM INITIALIZATIONS DO NOT SEEM TO DEGRADE  
THEIR SHORT RANGE FORECASTS.  
 
 
SYSTEM SIDESWIPING THE PACIFIC NORTHWEST MONDAY AFTERNOON  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CANADIAN BLEND; CONFIDENCE AVERAGE  
 
THERE'S SIGNIFICANT SPREAD WITH THIS SYSTEM, WITH THE 00Z CANADIAN  
WELL TO THE SOUTH/SLOW -- ITS USUAL BIAS. THE 06Z GEFS/00Z ECMWF  
ENSEMBLE MEAN SOLUTIONS SUPPORT SOMETHING FASTER, TOWARDS THE  
QUICKER 12Z GFS, 12Z NAM, 00Z ECMWF, AND 00Z UKMET CONSENSUS. A  
COMPROMISE OF THESE FOUR PIECES OF GUIDANCE IS PREFERRED WITH  
CONFIDENCE NO BETTER THAN AVERAGE.  
 
SHORTWAVE DROPPING INTO THE NORTHERN PLAINS SUNDAY NIGHT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: ECMWF/UKMET/GFS BLEND; CONFIDENCE AVERAGE  
 
THE GUIDANCE SHOWS ABOVE NORMAL DISPERSION ALOFT AND AT THE  
SURFACE. ALOFT, THE 00Z ECMWF/00Z UKMET SOLUTIONS ARE THE BEST  
FIT WITH THE TIMING OF THIS SHORTWAVE WITH THE 00Z CANADIAN THE  
FASTEST/DEEPEST. BECAUSE OF ISSUES ALOFT, SURFACE LOW POSITION  
ISSUES ARE VAST MONDAY EVENING, WITH THE 00Z CANADIAN AND 00Z  
UKMET/00Z ECMWF DEFINING THE NORTHEAST AND NORTHWEST SIDES OF THE  
BROAD 00Z GLOBAL ENSEMBLE SPREAD RESPECTIVELY. WITH A VERY STRONG  
UPSTREAM RIDGE, A MORE AMPLIFIED/SOUTHERN SOLUTION IS QUITE  
POSSIBLE, RULING OUT THE CANADIAN FROM CONSIDERATION. A  
COMPROMISE OF THE 00Z ECMWF, 00Z ECMWF, AND 12Z GFS IS ADVISED TO  
HELP DEAL WITH MODEL ISSUES AND TO ACCOUNT FOR EXPECTED PATTERN  
WITH AVERAGE CONFIDENCE.  
 
UPPER LOW MOVING INTO NORTHERN BAJA CA MONDAY  
PHASING SHORTWAVES ACROSS THE MID-ATLANTIC LATE SATURDAY  
SURFACE LOW MOVING OFFSHORE THE EAST COAST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
ANY DIFFERENCES SEEN IN THE GUIDANCE WITH THESE SYSTEMS ARE WITHIN  
THE NOISE LEVEL. A COMPROMISE OF THE 00Z CANADIAN, 00Z UKMET, 00Z  
ECMWF, 12Z GFS, AND 12Z NAM IS ADVISED WITH ABOVE AVERAGE  
CONFIDENCE. FOR PRECIPITATION/SNOW AMOUNT FORECAST THOUGHTS, SEE  
OUR QUANTITATIVE PRECIPITATION FORECAST (QPFPFD) AND PROBABILISTIC  
HEAVY SNOW AND ICING DISCUSSIONS (QPFHSD).  
 
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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