189  
FXUS10 KWNH 111837  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
236 PM EDT WED MAR 11 2020  
 
VALID MAR 11/1200 UTC THRU MAR 15/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..CLOSED LOW AFFECTING THE SOUTHWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/ECMWF/CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
   
..19Z UPDATE
 
 
ONLY VERY MINOR CHANGES WERE NOTED WITH THE 12Z ECMWF/UKMET/CMC  
COMPARED TO THEIR PREVIOUS 00Z CYCLES, SO NO CHANGES ARE  
RECOMMENDED FOR THE FINAL PREFERENCE.  
   
..PREVIOUS DISCUSSION FOLLOWS
 
 
ENSEMBLE SPAGHETTI PLOTS SUGGEST THE 00Z UKMET IS TOO SLOW, ALONG  
WITH THE 12Z NAM REGARDING THE WEAKENING MID-LEVEL CLOSED LOW AS  
IT TRACKS ACROSS THE SOUTHWEST THROUGH SATURDAY MORNING. DURING  
THE DAY ON SATURDAY, THE 12Z NAM BECOMES A SIGNIFICANTLY SLOWER  
OUTLIER WITH THE MID-LEVEL SHORTWAVE, BECOMING 500-600 MILES  
SLOWER THAN THE REMAINING MODEL CONSENSUS LATER IN THE DAY ON  
SATURDAY. THE 12Z GFS, 00Z ECMWF AND 00Z CMC AGREE REASONABLY WELL  
WITH ONE ANOTHER AND THE ENSEMBLE MEANS.  
 
...NORTHERN STREAM TROUGH TRACKING FROM THE NORTHERN ROCKIES,  
UPPER MIDWEST TOWARD THE NORTHEAST THROUGH FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
   
..19Z UPDATE
 
 
ONLY VERY MINOR CHANGES WERE NOTED WITH THE 12Z ECMWF/UKMET/CMC  
COMPARED TO THEIR PREVIOUS 00Z CYCLES, SO NO CHANGES ARE  
RECOMMENDED FOR THE FINAL PREFERENCE.  
   
..PREVIOUS DISCUSSION FOLLOWS
 
 
TIMING DIFFERENCES APPEAR WITH AN AMPLIFYING MID-LEVEL TROUGH  
EXPECTED TO TRACK ACROSS THE GREAT LAKES REGION THURSDAY NIGHT.  
THE 12Z NAM IS NOTABLY SLOWER WITH THE 00Z ECMWF/CMC A TOUCH  
SLOWER AS WELL COMPARED TO THE ENSEMBLE MEANS. MEANWHILE, THE 12Z  
GFS IS A LITTLE FASTER THAN THE ENSEMBLE MEANS REGARDING THE 500  
MB TROUGH AND ASSOCIATED SPEED SHEAR ENHANCED VORTICITY MAX  
ROUNDING THE BASE OF THE TROUGH.  
 
ENSEMBLE SCATTER LOW PLOTS SHOW A FAIR DEGREE OF NORTH/SOUTH  
SPREAD WITH THE SURFACE LOW CROSSING THE GREAT LAKES REGION INTO  
ONTARIO. THE 00Z UKMET/CMC ARE TOWARD THE SOUTHERN SIDE OF THE LOW  
TRACK SPREAD, ESPECIALLY THE 00Z UKMET. A BLEND OF THE 12Z GFS AND  
00Z ECMWF APPEARS TO BE THE BEST COMPROMISE FOR THIS SYSTEM.  
 
   
..CLOSED LOW DEVELOPING OVER PACIFIC NW FRIDAY/SATURDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
   
..19Z UPDATE
 
 
ONLY VERY MINOR CHANGES WERE NOTED WITH THE 12Z ECMWF/UKMET/CMC  
COMPARED TO THEIR PREVIOUS 00Z CYCLES, SO NO CHANGES ARE  
RECOMMENDED FOR THE FINAL PREFERENCE.  
   
..PREVIOUS DISCUSSION FOLLOWS
 
 
THE 12Z NAM IS THE ONLY MODEL TO SIGNIFICANTLY STAND OUT WITH AN  
EVENTUAL CLOSED LOW TO AFFECT THE NORTHWESTERN U.S. FOR THE END OF  
THE WEEK, WITH A DEEPER AND SLOWER PROGRESSION. THE NON 12Z-NAM  
GUIDANCE IS REASONABLY SIMILAR BUT THE 12Z GFS IS NOTED TO BE  
WEAKER WITH THE 700 MB LOW IN THE NORTHWEST COMPARED TO THE RATHER  
AGREEABLE 00Z ECMWF/UKMET/CMC. DESPITE THE DIFFERENCES OF THE 12Z  
GFS, AND COLDER LOW LEVEL AIR INTO MONTANA BY SATURDAY  
MORNING/AFTERNOON, WHEN BLENDED WITH THE 00Z ECMWF/UKMET/CMC, A  
PREFERRED BLEND IS REACHED.  
 
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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