757  
FXUS10 KWNH 311656  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1155 AM EST WED JAN 31 2018  
 
VALID JAN 31/1200 UTC THRU FEB 04/0000 UTC  
   
.SEE NOUS42 KWNO (ADMNFD) FOR UPPER AIR INGEST STATUS
 
 
   
..12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...COLD FRONT MOVING THROUGH THE GREAT LAKES TODAY AND THE LOWER  
MISSISSIPPI VALLEY TO THE MID-ATLANTIC THURSDAY NIGHT...  
...POSSIBLE SURFACE LOW DEVELOPMENT ALONG FRONT OVER SOUTHEASTERN  
QUEBEC EARLY FRIDAY MORNING WITH IMPACTS TO NORTHERN NEW ENGLAND...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/CMC BLEND  
CONFIDENCE: AVERAGE  
 
EXCEPT FOR THE GFS, THE DETERMINISTIC GUIDANCE HAS BEEN TRENDING  
SLOWER WITH LEADING EDGE OF THE 500 MB TROUGH MOVING INTO THE  
NORTHERN MID-ATLANTIC AND NORTHEAST U.S. EARLY FRIDAY MORNING. THE  
12Z NAM/GFS REMAIN A BIT FASTER THAN THE 00Z ECMWF/UKMET/CMC WITH  
THE TIMING OF THE COLD FRONT TO THE EAST COAST, BUT THESE TIMING  
DIFFERENCES ARE SOMEWHAT MINOR.  
 
REGARDING POSSIBLE SURFACE LOW DEVELOPMENT OVER EASTERN QUEBEC  
BETWEEN 00Z-12Z FEB 2, ECMWF ENSEMBLE MEMBERS ARE WELL CLUSTERED  
NEAR THE 00Z ECMWF, BUT THE GEFS AND CMC MEMBERS ARE SPARSE AND  
SPACED OUT. THE 00Z UKMET APPEARS ON ITS OWN WITH A SURFACE LOW  
FARTHER SOUTH OVER NORTHERN MAINE BY 12Z02, BUT THIS IDEA IS  
MOSTLY UNSUPPORTED IN THE ENSEMBLE GUIDANCE.  
 
THEREFORE, A 00Z ECMWF/CMC BLEND IS BEST FITTED TO THE TRENDS AND  
ENSEMBLE CLUSTERING.  
 
...WEAKENING MID-LEVEL SHORTWAVE APPROACHING THE NORTHWEST ON  
FRIDAY ALONG WITH PRECEDING ONSHORE FLOW...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/CMC BLEND  
CONFIDENCE: AVERAGE  
 
THROUGH 00Z/03, MODELS TRENDED TOWARD THE CONSISTENT GFS/ECMWF  
SOLUTION. HOWEVER, ENSEMBLE TRENDS SHOW TOWARD A BIT MORE  
AMPLIFIED WITH THE SHORTWAVE AS IT REACHES THE INTERMOUNTAIN WEST  
ON 12Z/03. THE 12Z GFS AND 00Z UKMET ARE ON THE MORE AMPLIFIED  
SIDE OF THE ENSEMBLE SPREAD, WHILE THE 12Z NAM IS MUCH  
FLATTER/WEAKER WITH THIS FEATURE. THE ENSEMBLE MEANS SUPPORT A  
MIDDLE GROUND IDEA, BEST SUPPORTED BY A 00Z ECMWF/CMC BLEND.  
 
...WEAK LOW LEVEL WAVE TRACKING THROUGH THE UPPER MIDWEST EARLY  
SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 70% 12Z GFS / 30% 00Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
DIFFERENCES ARE RATHER SIGNIFICANT WITH THE AMPLITUDE OF A WEAK  
LOW LEVEL WAVE FORECAST TO TRANSLATE ACROSS THE MIDDLE TO UPPER  
MISSISSIPPI VALLEY ON SATURDAY. THE 00Z CMC IS UNSUPPORTED WITH A  
RATHER DEVELOPED WAVE APPROACHING THE SOUTHERN ONTARIO/QUEBEC  
BORDER BY 00Z04, WITH ENSEMBLE SCATTER LOW PLOTS EXTENDING FROM  
NEAR JAMES BAY TO EASTERN NEBRASKA. THE 00Z ECMWF AND 00Z UKMET  
ARE LESS DEVELOPED WITH THE LOW LEVEL WAVE AND DO NOT DROP THE  
COLD FRONT EXTENDING WEST OF THE LOW FAR TO THE SOUTH.  
 
ENSEMBLE MEANS ARE SIMILAR VERSIONS OF THEIR DETERMINISTIC  
COUNTERPARTS AND SHOW REASONABLY CLOSE AGREEMENT BY 00Z/04, BUT  
THE 00Z ECMWF ENSEMBLE MEAN IS MORE AMPLIFIED THAN THE 00Z ECMWF.  
THEREFORE, A BLEND OF THE 00Z ECMWF AND 12Z GFS, WEIGHTED MORE TO  
THE 12Z GFS APPEARS BEST. THE 12Z NAM IS ON THE MORE  
AMPLIFIED/SLOWER SIDE FOR WHAT IT'S WORTH.  
 
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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