869  
FXUS10 KWNH 070638  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
137 AM EST TUE NOV 07 2017  
 
VALID NOV 07/0000 UTC THRU NOV 10/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..LINGERING COLD FRONT OVER THE SOUTH AND SOUTHEAST
 
 
...WEAK SURFACE LOW DEVELOPING OVER THE TENNESSEE VALLEY AND  
PROGRESSING ENE OVER THE WESTERN ATLANTIC...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
WITH RESPECT TO THE MASS FIELDS RELATED TO THE STALLED FRONT OVER  
THE SOUTH...THE MODELS SHOW QUITE A BIT OF SIMILARITY...AND A  
GENERAL MODEL BLEND IS RECOMMENDED WITH HIGH CONFIDENCE.  
 
06Z UPDATE: NONE. MODELS CONTINUE TO BE IN GOOD AGREEMENT.  
 
...POSITIVELY TILTED TROUGH TRANSLATING FROM THE INTERIOR WEST  
TODAY...TO THE PLAINS BY WEDNESDAY...SOUTHEAST BY THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z GFS / 00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ENSEMBLE CLUSTERS (GEFS AND ECMWF) FROM THE 12Z MODEL CYCLE  
INDICATE THAT THE VAST MAJORITY OF SOLUTIONS ARE CLOSEST TO THE  
00Z GFS AND 12Z ECMWF. A BLEND OF THE GFS AND ECMWF WAS THE  
PREVIOUS PREFERENCE...AND GIVEN THE SUPPORT FROM THE ENSEMBLE  
MEMBERS...A CONSISTENT APPROACH APPEARS REASONABLE. THE SPREAD  
ASSOCIATED WITH THIS DIGGING TROUGH APPEARS TO PRIMARILY BE  
RELATED TO TIMING. THE 00Z NAM IS NOTABLY SLOW WITH THE  
PROGRESSION OF THE TROUGH...AND LIES ON THE EXTREME OF AVAILABLE  
GLOBAL ENSEMBLE MEMBERS. MEANWHILE...THE 12Z CMC IS ON THE  
OPPOSITE END OF THE SPECTRUM AND SHOWS A MUCH FASTER PROGRESSION  
(BY ABOUT 6HR RELATIVE TO THE 00Z GFS AND 12HR RELATIVE TO THE 12Z  
ECMWF). THE 00Z UKMET SHOWS TIMING ROUGHLY IN BETWEEN THAT OF THE  
GFS AND ECMWF...BUT IS FAR STRONGER WITH THE VORT MAX ALOFT...AND  
DOES SHOW SOME EFFECTS FROM THIS IN THE LOW LEVELS...WITH EARLIER  
AND STRONGER CYCLOGENESIS NEAR THE EASTERN GULF COAST ON THURSDAY  
MORNING. NO OTHER MODEL IS SHOWING THIS. THEREFORE...THE  
PREFERENCE IS TO CONTINUE TO LEAN TOWARD A BLEND OF THE GFS AND  
ECMWF AS THEY BETTER FIT THE HIGHER PROBABILITY OUTCOMES PROPOSED  
BY ENSEMBLES.  
 
06Z UPDATE: MODEL PREFERENCE REMAINS THE SAME -- A GFS AND ECMWF  
BLEND. THE 00Z ECMWF HAS TRENDED TOWARD THE GFS IN TERMS OF TIMING  
OF THIS WAVE. THE 00Z UKMET HAS AS WELL...BUT IS FAR STRONGER WITH  
A SECONDARY WAVE FURTHER TO THE SOUTHWEST...WHICH IS A SUBSTANTIAL  
OUTLIER.  
 
...DEEP CYCLONE DROPPING FROM THE GULF OF ALASKA TO OFFSHORE OF  
THE PACIFIC NORTHWEST...   
..OPENING INTO A TROUGH OVER THE NORTHWEST BY FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z NAM / 00Z UKMET / 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
MODELS ARE IN FAIRLY GOOD AGREEMENT THROUGH ABOUT 48 HOURS...BUT  
DIFFERENCES BEGIN TO EMERGE AS THE CYCLONE APPROACHES THE COAST  
LATE IN THE WEEK. THE MAIN DIFFERENCE APPEARS TO BE RELATED TO HOW  
QUICKLY THE MODELS DEVOLVE THE CYCLONE INTO AN OPEN WAVE AND THEN  
DEAMPLIFY THAT WAVE AS IT MOVES INTO THE NORTHWEST. THE 00Z GFS  
AND 12Z CMC ARE FASTEST WITH THAT PROCESS...BRINGING A WEAKER WAVE  
ONSHORE SOONER THAN THE OTHER MODELS. HOWEVER...THE 00Z NAM...00Z  
UKMET...AND 12Z ECMWF MAINTAIN A STRONGER TROUGH OFFSHORE FOR A  
LITTLE LONGER. THE LATTER SOLUTION GENERALLY KEEPS THE TROUGH AXIS  
OFFSHORE THROUGH 12Z FRIDAY. THIS IS SUPPORTED BY A MAJORITY OF  
THE ECMWF AND GEFS ENSEMBLE MEMBERS...SO THE PREFERENCE IS TO LEAN  
IN THAT DIRECTION AS WELL. WITH SUCH A STRONG CYCLONE INITIALLY  
(AND THROUGH 36-48 HOURS)...IT MAY ALSO TAKE SOME TIME TO DEVOLVE  
INTO AN OPEN WAVE.  
 
06Z UPDATE: MODEL PREFERENCE REMAINS THE SAME. MODELS HAVE  
GENERALLY REMAINED CONSISTENT WITH PRIOR SOLUTIONS...AND THE 00Z  
CMC IS PERHAPS SLIGHTLY SLOWER AND STRONGER WITH THE TROUGH AS IT  
MOVES ASHORE.  
 
...SOUTHERN END OF DEEP UPPER TROUGH LOCATED OVER THE NORTH  
CENTRAL U.S. BY THU MORNING...   
..COLD FRONT SWEEPING INTO THE NORTHERN STATES WED-FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z GFS / 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
OVERALL...THE MODEL AGREEMENT WITH THIS SYSTEM IS FAIRLY GOOD.  
THERE ARE DIFFERENCES IN THE PRECISE STRUCTURE OF THE  
TROUGH...HOWEVER. THE 00Z GFS AND 12Z ECMWF DEPICT A SHARPER  
TROUGH OVERALL...WITH THE CORE OF THE TROUGH DIGGING FURTHER SOUTH  
AND SOUTHEAST INTO PORTIONS OF THE US. THIS BECOMES EVIDENT BY  
FRIDAY IN THE MID-UPPER LEVEL HEIGHT FIELDS AND THICKNESS  
FIELDS...WITH THE 00Z UKMET...12Z CMC...AND 00Z NAM GENERALLY  
SHOWING A BROADER WAVE AND KEEPING THE CORE OF THE TROUGH A LITTLE  
FURTHER NORTH INTO CANADA. THE GFS AND ECMWF ARE CLOSER TO THE  
ENSEMBLE MEANS (INCLUDING THE 12Z CANADIAN ENSEMBLE MEAN) SO THE  
PREFERENCE IS TO LEAN IN THAT DIRECTION.  
 
06Z UPDATE: MODEL PREFERENCE REMAINS THE SAME. THE 00Z ECMWF  
CONTINUES TO SHOW A SHARPER TROUGH...ALTHOUGH IT HAS BACKED OFF A  
BIT ON HOW FAR SOUTHEAST THE WAVE DIGS. OVERALL...MODELS CONTINUE  
TO BE IN FAIRLY GOOD AGREEMENT. THE PREFERENCE REMAINS THE SAME AS  
THE GFS AND ECMWF HAVE BEEN CLOSER TO THE ENSEMBLE MEANS AND THE  
CHANGES ON THE 00Z MODEL CYCLE WERE NOT SUBSTANTIAL.  
 
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