180  
FXUS10 KWNH 081716  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1216 PM EST THU MAR 08 2018  
 
VALID MAR 08/1200 UTC THRU MAR 12/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
 
 
...COASTAL LOW CURRENTLY NEAR COASTAL MAINE, WEAKENING WESTWARD  
INTO SOUTHERN QUEBEC THROUGH FRIDAY MORNING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
   
..SECONDARY SURFACE LOW NEAR NOVA SCOTIA FRIDAY NIGHT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-00Z CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
BY 00Z/10, THE 00Z CMC STILL REMAINS A LITTLE BIT FARTHER EAST  
THAN THE REMAINING DETERMINISTIC CONSENSUS WITH THE SURFACE LOW.  
THE LATEST ENSEMBLE SCATTER LOW PLOTS CONTINUE TO SHOW A MODEST  
AMOUNT OF SPREAD BETWEEN 00Z-12Z/10, WITH THE 00Z CMC ON THE  
EASTERN END OF THE ENSEMBLES. THE NON-00Z CMC MODELS SHOW MINOR  
DIFFERENCES WITH LOCATION AND STRENGTH, BUT A BLEND OF THESE IS  
CONSIDERED A REASONABLE COMPROMISE WITH THIS SYSTEM.  
 
...SHORTWAVE DROPPING SOUTH ACROSS BRITISH COLUMBIA THURSDAY NIGHT  
WITH THE SOUTHERN PORTION REACHING INTO THE PLAINS SATURDAY...  
...SURFACE LOW DEVELOPING OVER THE SOUTHERN PLAINS LATE SATURDAY  
AND MOVING TOWARD THE SOUTHEAST ON SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/06Z GEFS/00Z ECMWF/00Z CMC BLEND  
CONFIDENCE: BELOW AVERAGE  
 
THE SHORTWAVE COMING THROUGH SOUTHWESTERN CANADA SHOWS SOME  
DIFFERENCES IN THE MODELS EARLY ON WITH THE 12Z NAM AND 00Z ECMWF  
LESS AMPLIFIED ACROSS THE SOUTHERN PORTION OF THE TROUGH COMPARED  
TO THE 12Z GFS/00Z UKMET/00Z CMC. THESE DIFFERENCES GROW  
DOWNSTREAM INTO THE PLAINS WITH LITTLE AGREEMENT SEEN AMONG THE  
MODELS. MOST MODEL RUN TO RUN CONTINUITY IS POOR, WITH PERHAPS THE  
GFS SHOWING THE MOST CONSISTENCY. HOWEVER, THE 12Z GFS APPEARS TO  
BE A STRONGER OUTLIER WITH ITS SURFACE LOW AS IT DEVELOPS AND  
TRACKS ACROSS THE SOUTH.  
 
AT 500 MB, ENSEMBLES AND THE MAJORITY OF DETERMINISTIC GUIDANCE  
SHOWS A TREND TOWARD WITH THE MID-LEVEL TROUGH EAST OF THE  
MISSISSIPPI RIVER ON SUNDAY INTO MONDAY. WHILE ENSEMBLE SCATTER  
LOW PLOTS SHOW A MODERATE TO LARGE DEGREE OF SPREAD ON SUNDAY, A  
CENTER POINT OF THE LOWS, WHEN CONSIDERING TRENDS, IS NEAREST THE  
POSITION OF THE 12Z GFS AND 00Z CMC. THE 00Z ECMWF APPEARS TOO  
WEAK WITH THE SYSTEM AND THE 12Z NAM SIGNIFICANT FASTER, WHILE THE  
00Z UKMET APPEARS TOO FAR TO THE SOUTH.  
 
NO SINGLE MODEL OR TWO-WAY BLEND IS PREFERRED HERE GIVEN THE LARGE  
DIFFERENCES AND POOR RUN TO RUN CONSISTENCY. THEREFORE, A  
MULTI-MODEL BLEND OF THE 12Z GFS/06Z GEFS/00Z ECMWF/00Z CMC IS  
PREFERRED WITH HOPEFULLY THE STRENGTHS OF EACH MODEL BEING  
MAXIMIZED WHILE MINIMIZING APPARENT WEAKNESSES.  
 
...WEAK SHORTWAVE APPROACHING CALIFORNIA FROM THE WEST SATURDAY  
EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/00Z ECMWF/00Z UKMET BLEND  
CONFIDENCE: AVERAGE  
 
THE 00Z ECMWF IS MUCH FASTER WITH THE SHORTWAVE COMING INTO  
CALIFORNIA THAN MANY OF THE LATEST ENSEMBLE GUIDANCE, WHILE THE  
12Z GFS IS SLOWER BUT WEAKER. THE 00Z UKMET IS ALSO ON THE SLOW  
SIDE BUT APPEARS TO BE A FAVORABLE AMPLITUDE. GIVEN THE SOUTHERN  
STREAM JET STREAM IS RATHER ZONAL ACROSS THE PACIFIC WITH A  
MERIDIONAL NORTHERN STREAM, THE PREFERENCE IS NOT BE TOWARD THE  
SLOWER SIDE OF THE MODELS. WITH A WEAKER AMPLITUDE SYSTEM LIKE THE  
12Z GFS, A SLOWER/WEAKER SOLUTION DOES NOT FIT THE CONCEPTUAL  
MODEL, SO A MIDDLE GROUND BETWEEN THE 12Z GFS/00Z ECMWF/00Z UKMET  
IS RECOMMENDED AT THIS TIME.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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