630   
FXUS10 KWNH 260423  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1122 PM EST WED DEC 25 2019  
  
VALID DEC 26/0000 UTC THRU DEC 29/1200 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
00Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
  
SYSTEM APPROACHING PACIFIC NORTHWEST SUNDAY MORNING  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE:  GFS/UKMET COMPROMISE  
CONFIDENCE:  ABOVE AVERAGE  
  
THERE ARE COMPETING FACTORS CLOUDING THE FORECAST PICTURE ACROSS  
THE PACIFIC NORTHWEST AND PLAINS/MIDWEST BY SUNDAY.  A SYSTEM  
APPROACHING THE PACIFIC NORTHWEST AT THAT TIME HAS A BUILDING  
RIDGE SEEN IN ALL THE GUIDANCE IN ITS WAKE, WHICH SHOULD YIELD A  
STRENGTHENING SYSTEM ALOFT MOVING TOWARDS THE REGION.  THE 12Z  
ECMWF WAS OUT OF TOLERANCE WITH THIS SYSTEM AS IT MOVED A SHARP  
SHORTWAVE OUT IN ADVANCE OF IT WHICH WAS NOT SEEN IN ANY OF THE  
OTHER GUIDANCE AND LIKELY LED TO TOO WEAK OF A LOOK WITH THE  
SYSTEM NEAR 47N 130W SUNDAY MORNING (EVEN WHEN COMPARED TO ITS  
ENSEMBLE MEAN).  A COMPROMISE OF THE 00Z GFS/12Z UKMET LOOKS IDEAL  
WITH THE NORTHWEST SYSTEM WITH ABOVE AVERAGE CONFIDENCE.  
  
SYSTEM MOVING FROM THE WEST INTO THE MIDWEST FRI-SUN  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE:  ECMWF/UKMET/CANADIAN COMPROMISE  
CONFIDENCE:  AVERAGE  
  
DOWNSTREAM, THE GUIDANCE IS PLAGUED WITH STREAM INTERACTION AS THE  
SYSTEM MOVING FROM THE WEST INTO THE PLAINS STARTS OUT UNPHASED  
BUT BECOMES PHASED WITH TIME AS A SHARPLY AMPLIFIED RIDGE BUILDING  
INTO WESTERN CANADA.  THE QUICKEST SOLUTIONS WITH THE  
PLAINS/MIDWEST SYSTEM ARE THE 00Z GFS AND 00Z NAM.  SINCE THE FLOW  
OVERALL IS BECOMING MORE AMPLIFIED, A SLOWER SOLUTION IN THE  
PLAINS/MIDWEST IS PREFERRED BY SUNDAY MORNING SINCE THE KICKING  
INFLUENCE OF THE SYSTEM APPROACHING THE PACIFIC NORTHWEST  
SHOULDN'T BE FELT QUITE YET (OVER 15 DEGREES LATITUDE/900 MILES  
AWAY).  PREFER A COMPROMISE OF THE 12Z ECMWF/12Z UKMET/12Z  
CANADIAN WITH THE PLAINS/MIDWESTERN SYSTEM WITH AVERAGE CONFIDENCE.  
  
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
  
ROTH  
  
 
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