448  
FXUS10 KWNH 081838  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
137 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 MODEL EVALUATION WITH FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
 
 
...COASTAL LOW CURRENTLY NEAR COASTAL MAINE, WEAKENING WESTWARD  
INTO SOUTHERN QUEBEC THROUGH FRIDAY MORNING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
   
..SECONDARY SURFACE LOW NEAR NOVA SCOTIA FRIDAY NIGHT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z CMC ADJUSTED TOWARD THE MODEL CONSENSUS SO THAT BY 00Z/10,  
THE 12Z CMC NO LONGER APPEARS TO BE FARTHER EAST COMPARED TO THE  
REMAINING DETERMINISTIC CONSENSUS WITH THE SURFACE LOW, LIKE THE  
00Z CMC. THE LATEST ENSEMBLE SCATTER LOW PLOTS CONTINUE TO SHOW A  
MODEST AMOUNT OF SPREAD BETWEEN 00Z-12Z/10, WITH THE 12Z CMC AND  
REMAINING 12Z GUIDANCE AGREEING TOWARD THE MIDDLE OF THOSE  
ENSEMBLE DIFFERENCES.  
 
...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/12Z GEFS/00Z ECMWF/12Z CMC BLEND  
CONFIDENCE: BELOW AVERAGE  
 
THE SHORTWAVE COMING THROUGH SOUTHWESTERN CANADA SHOWS SOME  
DIFFERENCES IN THE MODELS EARLY ON WITH THE 12Z NAM LESS AMPLIFIED  
ACROSS THE SOUTHERN PORTION OF THE TROUGH COMPARED TO THE 12Z  
GFS/ECMWF/UKMET/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 OVER THE WEEKEND. 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 STRONGER WITH THE MID-LEVEL TROUGH EAST OF  
THE MISSISSIPPI RIVER ON SUNDAY INTO MONDAY. THE IS CONTRARY TO  
THE 12Z ECMWF WHICH TRENDED MUCH WEAKER FOR SUNDAY ACROSS THE  
SOUTH. 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 12Z  
CMC VALID 00Z/11 TO 00Z/12. THE 12Z ECMWF APPEARS TOO WEAK WITH  
THE SYSTEM AT 500 MB WHILE BEING TOO FAR SOUTH AT THE SURFACE,  
SOUTH OF MOST OF THE LATEST ENSEMBLE LOW PLOTS AND APPEARING WORSE  
THAN THE 00Z ECMWF. THE 12Z NAM IS SIGNIFICANT FASTER AT THE  
SURFACE WHILE THE 12Z UKMET ALSO APPEARS TOO FAR TO THE SOUTH LIKE  
THE ECMWF, APPEARING WORSE-OFF THAN ITS 00Z CYCLE.  
 
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/12Z GEFS/00Z ECMWF/12Z 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/ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
THE 00Z ECMWF IS MUCH FASTER WITH THE SHORTWAVE COMING INTO  
CALIFORNIA THAN MANY OF THE LATEST ENSEMBLE GUIDANCE BUT THE 12Z  
ECMWF SLOWED DOWN SOME. THE 12Z GFS/UKMET ARE SLOWER AND WEAKER  
THAN THE ECMWF BUT THE 12Z UKMET SPLITS THE DIFFERENCE BETWEEN THE  
STRONGER ECMWF AND WEAKER GFS. GIVEN THE SOUTHERN STREAM JET IS  
RATHER ZONAL ACROSS THE PACIFIC WITH A MERIDIONAL NORTHERN STREAM  
JET, 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/ECMWF/UKMET IS RECOMMENDED AT  
THIS TIME WHICH IS REASONABLY CLOSE TO THE LATEST ENSEMBLE MEANS.  
 
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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