572  
FXUS10 KWNH 311843  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
142 PM 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 MODEL EVALUATION WITH FINAL 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: 12Z ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
ALTHOUGH THE 12Z ECMWF?UKMET/CMC TRENDED FASTER WITH THEIR 12Z  
RUNS, TRENDS HAD BEEN SLOWER PREVIOUSLY AND THE 12Z GFS REMAINS  
THE FASTEST WITH THE 500 MB TROUGH MOVING INTO THE NORTHERN  
MID-ATLANTIC AND NORTHEAST U.S. EARLY FRIDAY MORNING. WHILE THE  
12Z GFS IS QUICKEST, ANY LINGERING 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/12Z ECMWF, BUT THE GEFS AND CMC MEMBERS ARE SPARSE  
AND SPACED OUT. THE 12Z UKMET TRENDED NEAR THE ECMWF BUT LIES A  
LITTLE NORTH OF IT, A MORE SUPPORTED SOLUTION COMPARED TO THE 00Z  
UKMET. THE 12Z CMC IS A BIT MORE DEVELOPED AND SOUTH WITH THE  
SURFACE LOW EARLY ON FRIDAY, HOLDING LITTLE SUPPORT.  
 
THEREFORE, A 12Z ECMWF/UKMET 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: 12Z ECMWF/UKMET/CMC BLEND  
CONFIDENCE: AVERAGE  
 
THROUGH 00Z/03, MODELS TRENDED TOWARD THE CONSISTENT GFS/ECMWF  
SOLUTION COMPARED TO TUESDAY'S RUNS. HOWEVER, ENSEMBLE TRENDS SHOW  
TOWARD A BIT MORE AMPLIFIED WITH THE SHORTWAVE AS IT REACHES THE  
INTERMOUNTAIN WEST ON 12Z/03. THE 12Z GFS IS 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/UKMET/CMC BLEND.  
WHILE THERE IS A DECENT AMOUNT OF CONSISTENCY FOR THE 12Z  
ECMWF/UKMET/CMC IDEA, THERE IS STILL ENOUGH SPREAD IN THE ENSEMBLE  
GUIDANCE AND RUN TO RUN CHANGES TO ONLY KEEP CONFIDENCE AVERAGE.  
 
...WEAK LOW LEVEL WAVE TRACKING THROUGH THE UPPER MIDWEST EARLY  
SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z 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 12Z 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 12Z ECMWF AND 12Z UKMET,  
LIKE THEIR 00Z CYCLES, REMAIN LESS DEVELOPED WITH THE LOW LEVEL  
WAVE AND DO NOT DROP THE COLD FRONT EXTENDING WEST OF THE LOW FAR  
AS QUICKLY TO THE SOUTH WHEN COMPARED TO THE REMAINING  
DETERMINISTIC GUIDANCE. HOWEVER, THE 12Z ECMWF/UKMET DID TREND  
TOWARD THE REMAINING QUICKER MODEL CONSENSUS.  
 
ENSEMBLE MEANS ARE SIMILAR VERSIONS OF THEIR DETERMINISTIC  
COUNTERPARTS AND SHOW REASONABLY CLOSE AGREEMENT BY 00Z/04, AND  
THE 12Z ECMWF IS NOW CLOSER TO THE 00Z ECMWF ENSEMBLE MEAN WITH  
THE COLD FRONT AND LOW LEVEL WAVE. THEREFORE, A 50/50 BLEND OF THE  
12Z ECMWF AND 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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