793  
FXUS10 KWNH 041643  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1143 AM EST THU JAN 04 2018  
 
VALID JAN 04/1200 UTC THRU JAN 08/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..DEEP CYCLONE PUSHING INTO THE CANADIAN MARITIMES BY FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS ARE GENERALLY IN GOOD AGREEMENT ON THE PROGRESSION OF THE  
DEEP OCCLUDED CYCLONE TO THE NORTHEAST...AND THE OVERALL PATTERN  
AS IT BEGINS TO FILL OVER THE CANADIAN MARITIMES INTO THE WEEKEND.  
THEREFORE A GENERAL MODEL BLEND IS PREFERRED.  
 
   
..UPPER LEVEL TROUGH APPROACHING WEST COAST ON FRIDAY
 
 
...SPLITTING INTO NORTHERN AND SOUTHERN STREAM WAVES AND PUSHING  
INTO THE PLAINS THIS WEEKEND...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: THROUGH 48H -- GENERAL MODEL BLEND  
AFTER 48H -- BLEND OF 12Z GFS AND 00Z UKMET/ECMWF  
CONFIDENCE: AVERAGE  
 
MODELS HAVE MOVED INTO SOMEWHAT BETTER AGREEMENT THROUGH THE FIRST  
48 HOURS OF THE FORECAST (THROUGH 05/12Z) AS THE TROUGH APPROACHES  
THE PACIFIC NORTHWEST...AND A GENERAL BLEND AT THE EARLY HOURS OF  
THE FORECAST IS THE PREFERENCE. AFTER THAT...GREATER DIFFERENCES  
EMERGE WITH VARIABILITY LIKELY DUE TO THE COMPLEXITIES OF EMBEDDED  
+PV ANOMALIES IN THE APPROACHING TROUGH AND THAT THIS WILL BE THE  
BEGINNING OF A PATTERN CHANGE. HOWEVER...THE MODELS ALL DO SHOW  
THE SAME GENERAL IDEA OF THE TROUGH SPLITTING INTO TWO PRIMARY  
WAVES -- THE FIRST MOVING ACROSS SOUTHERN CANADA AND THE SECOND  
DIGGING THROUGH THE INTERMOUNTAIN WEST INTO THE SOUTHERN PLAINS.  
 
WITH THE NORTHERN WAVE...PRIMARY DIFFERENCES APPEAR TO BE RELATED  
TO TIMING. THE 12Z NAM IS FASTER AND FURTHER SOUTHEAST WITH THE  
WAVE BY SATURDAY NIGHT...WHILE THE 00Z CMC IS SLOWER. BETTER  
AGREEMENT ON TIMING EXISTS WITH THE 12Z GFS...00Z ECMWF...AND 00Z  
UKMET...WHICH ALSO ALIGN BETTER WITH THE ENSEMBLE MEANS.  
 
FOR THE SOUTHERN WAVE...THE GFS...UKMET...AND ECMWF ALSO APPEAR TO  
BE THE MOST SIMILAR...WITH THE CMC DEPICTING A MUCH BROADER WAVE  
AND THE NAM STRONGER AND FURTHER SOUTH. THE PREFERENCE IS FOR A  
BLEND OF THE GFS...ECMWF...AND UKMET AS THESE ARE CLOSEST TO THE  
ENSEMBLE MEANS AND THUS REPRESENT A MORE LIKELY COMPROMISE  
SOLUTION AT THIS TIME.  
 
...NEXT UPPER LEVEL TROUGH APPROACHING THE PACIFIC NORTHWEST  
BEGINNING LATER ON SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS AND 00Z UKMET/ECMWF  
CONFIDENCE: AVERAGE  
 
THE 00Z CMC SHOWS A MORE CONCENTRATED WAVE FURTHER NORTH WITH THIS  
APPROACHING TROUGH...AND THE DEEPEST SURFACE LOW OFF BRITISH  
COLUMBIA. THIS IS NOT SUPPORTED BY OTHER MODELS...AND DOES AFFECT  
ITS PLACEMENT OF SENSIBLE WEATHER IMPACTS. THE 12Z NAM SHOWS A  
BROADER TROUGH ALOFT AND ONLY HAS A VERY WEAK REFLECTION AT THE  
SURFACE...WHICH IS DIFFERENT FROM THE GFS...UKMET...AND ECMWF  
WHICH ALL HAVE A SUB-1000MB LOW OFFSHORE OF CENTRAL BRITISH  
COLUMBIA BY 08/00Z. THEREFORE...THE PREFERENCE IS TO LEAN TOWARD A  
BLEND OF THE GFS...UKMET...AND ECMWF WHICH ARE MOST SIMILAR AND  
HAVE A SURFACE LOW POSITION CLOSEST TO THE ECMWF ENSEMBLE MEAN.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page