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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