136  
FXUS10 KWNH 071658  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1157 AM EST THU DEC 07 2017  
 
VALID DEC 07/1200 UTC THRU DEC 11/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..STALLED FRONT ACROSS THE SOUTHERN CONUS / GULF COAST
 
 
...DIGGING SHORTWAVE IN NM/TX ROUNDING THE BASE OF THE TROUGH AND  
MOVING ALONG THE GULF COAST FRI NGT AND SAT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z NAM / 12Z UKMET / 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
DESPITE THE MAIN IMPACTS FROM THIS SYSTEM ONLY BEING ABOUT 12-36  
HOURS AWAY...THERE IS STILL A FAIR AMOUNT OF MODEL DISAGREEMENT ON  
SOME OF THE SPECIFICS -- PRIMARILY RELATED TO THE INTENSITY OF THE  
CORE OF THE SHORTWAVE AND TIMING. THE 12Z GFS HAS TRENDED VERY  
SLIGHTLY SLOWER WITH THE EJECTING SHORTWAVE...BUT STILL REMAINS ON  
THE FAST END OF GUIDANCE AND APPEARS TO INCREASINGLY BE AN OUTLIER  
IN THAT REGARD. MORE OF THE MODELS SEEM TO SHOW A TIMING ABOUT 6  
HOURS SLOWER...SO THE PREFERENCE IS TO LEAN IN THAT DIRECTION WITH  
RESPECT TO TIMING.  
 
OVERALL THERE HAS BEEN A CONVERGENCE OF MODEL SPREAD IN TERMS OF  
THE EXPECTED AMPLITUDE OF THE WAVE AS IT EJECTS EAST ALONG THE  
GULF COAST. THE NAM AND CMC WERE ON THE MORE AMPLIFIED END OF  
GUIDANCE SEVERAL MODEL CYCLES AGO AND HAVE SLIGHTLY TRENDED TOWARD  
THE CONSENSUS. MEANWHILE THE GFS WAS ON THE LESS AMPLIFIED END OF  
GUIDANCE AND HAS ALSO TRENDED TOWARD THE CONSENSUS. THAT BEING  
SAID...THERE STILL REMAINS SOME DISAGREEMENT IN THIS RESPECT IN  
ADDITION TO THE TIMING DIFFERENCES. THE NEW 12Z UKMET...12Z NAM  
AND 00Z ECMWF ARE VERY SIMILAR IN THEIR TIMING...BUT OFFER A  
REASONABLE SPREAD OF POSSIBLE SOLUTIONS WITH RESPECT TO THE  
STRENGTH OF THE WAVE AS IT TRENDS EAST...IN ADDITION TO OTHER MASS  
FIELDS. THE NAM IS CURRENTLY THE MOST AMPLIFIED WITH COLDEST  
LOW-MID LEVEL TEMPERATURE PROFILE...THE UKMET IN THE MIDDLE...AND  
THE ECMWF ON THE LESS AMPLIFIED END OF GUIDANCE.  
 
...SHORTWAVE DIGGING FROM THE ARCTIC CIRCLE IN NW CANADA TO THE  
WESTERN GREAT LAKES BY SATURDAY MORNING...   
..PHASING WITH SHORTWAVE EJECTING UP THE EAST COAST
 
   
..SURFACE LOW DEVELOPMENT JUST OFF THE EASTERN SEABOARD
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z NAM / 00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE AFOREMENTIONED SYSTEM ALONG THE GULF COAST WILL PLAY A ROLE UP  
THE EAST COAST AS THE ASSOCIATED EJECTING WAVE TRANSLATES  
NORTHEAST AND BEGINS TO PHASE WITH A DIGGING SHORTWAVE THROUGH THE  
GREAT LAKES REGION. THE RESULT SHOULD BE SURFACE CYCLOGENESIS  
ABOUT 250-300KM OFF THE EAST COAST. THE OVERALL TREND WITH THIS  
LOW OVER THE PAST SEVERAL MODEL CYCLES HAS BEEN TO NUDGE THE LOW  
TRACK CLOSER TO THE COAST. THIS IS EVIDENT IN THE GEFS AND ECMWF  
ENSEMBLE MEANS...AS WELL AS THE OPERATIONAL MODELS. ALL OF THE 12Z  
OPERATIONAL RUNS THAT ARE AVAILABLE SO FAR (NAM, GFS, UKMET) LOOK  
VERY SIMILAR IN TERMS OF LOW TRACK...BUT THE GFS IS STILL FASTER  
WITH TIMING BY APPROXIMATELY 6 HOURS. THE 00Z CMC AND 00Z ECMWF  
ARE STILL ABOUT A DEGREE OR TWO OF LONGITUDE EAST...BUT GIVEN THE  
OVERALL TRENDS...THEY MAY SHOW MORE SIMILARITY ON THE 12Z RUNS  
WHEN THEY ARRIVE. THE PREFERENCE WILL BE FOR A BLEND OF THE  
NAM...UKMET...AND ECMWF...WITH A SLIGHTLY HIGHER WEIGHT GIVEN TO  
THE NAM/UKMET SOLUTION OVERALL AS THE TREND IS IN THAT DIRECTION.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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