625  
FXUS10 KWNH 230441  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1141 PM EST SUN DEC 22 2019  
 
VALID DEC 23/0000 UTC THRU DEC 26/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH PREFERENCE AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z GFS, 12Z CMC, 12Z UKMET  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH TUESDAY NIGHT (AROUND  
25.06Z) AND A GENERAL MODEL BLEND FOR THIS TIME PERIOD WOULD BE A  
REASONABLE FORECAST PREFERENCE ACROSS MOST OF THE COUNTRY. AN  
IMPORTANT DIVERGENCE IN MODEL GUIDANCE OCCURS WITH THE TROUGH  
ALONG THE WEST COAST ON WEDNESDAY. A REINFORCING SHORTWAVE IS  
FORECAST TO DIG SHARPLY SOUTHEAST FROM THE GULF OF ALASKA AND LEAD  
TO CLOSED LOW DEVELOPMENT SOMEWHERE IN THE VICINITY OF CALIFORNIA.  
 
THE 12Z ECMWF -- AND THE VAST MAJORITY OF ITS ENSEMBLE MEMBERS --  
DIGS THE WAVE WITH MORE OF A SOUTHERLY COMPONENT RELATIVE TO MANY  
OF THE OTHER MODELS. THIS EVENTUALLY LEADS TO A MID-UPPER LEVEL  
CLOSED LOW FURTHER TO THE WEST BY 26.12Z, A SURFACE LOW FURTHER  
OFFSHORE OF THE SOUTHERN CALIFORNIA COAST, AND HEIGHT FALLS ALOFT  
CONSTRAINED CLOSER TO THE COAST. THE QPF IN THE INTERIOR WEST IS  
ALSO LOWER.  
 
MEANWHILE, THE 00Z GFS IS FASTER WITH SPREADING HEIGHT FALLS INTO  
THE WEST AND HAS A SURFACE LOW CLOSER TO THE CALIFORNIA COAST. IT  
IS JOINED BY THE 00Z NAM, 12Z CMC AND 12Z UKMET. NORMALLY AS AN  
EVENT DRAWS NEARER IN TIME, DIFFERENT MODELS WILL BEGIN TO  
CONVERGE ON A COMMON SCENARIO. IN THIS CASE, INDIVIDUAL ENSEMBLES  
HAVE SEEN THEIR SPREAD NARROW, BUT THE GAP BETWEEN THE ECMWF, GEFS  
AND CMC HAS NOT NARROWED SUBSTANTIALLY OVER THE PAST COUPLE MODEL  
CYCLES.  
 
IN THIS CASE, THE PREFERENCE IS TO LEAN TOWARD THE GFS, CMC AND  
UKMET, GIVEN GREATER SUPPORT FROM A VARIETY OF DIFFERENT MODELS.  
THIS ALSO ALIGNS MORE CLOSELY WITH THE WPC MEDIUM RANGE FORECAST  
PREFERENCE, WHICH APPLIED SLIGHTLY GREATER WEIGHT TO THE GFS AND  
UKMET AT THE BEGINNING OF THE MEDIUM RANGE PERIOD.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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