687  
FXUS10 KWNH 100650  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
249 AM EDT TUE OCT 10 2017  
 
VALID OCT 10/0000 UTC THRU OCT 13/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..00Z MODEL EVALUATION...INCLUDING FINAL PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...PLAINS TROUGH DEAMPLIFYING AND ACCELERATING TO THE NORTHEAST  
U.S. BY THURSDAY AND ACCOMPANYING WEAK SURFACE LOW IN THE UPPER  
MIDWEST / OHIO VALLEY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS / 12Z ECMWF ENS MEAN  
CONFIDENCE: AVERAGE  
 
THERE APPEAR TO BE TWO DISTINCT CAMPS WITH THIS SYSTEM: (1) THE  
00Z ECMWF...00Z UKMET AND MANY OF THE 12Z ECMWF ENSEMBLE MEMBERS  
WHICH CONTINUE TO SHOW A STRONGER VORT MAX AT THE CORE OF THE  
TROUGH -AND- (2) MOST OF THE REMAINING OPERATIONAL MODELS AND GEFS  
ENSEMBLE MEMBERS. DIFFERENCES ARE NOT SUBSTANTIAL IN THE MASS  
FIELDS THROUGH THE FIRST 24-36 HOURS...BUT AFTER THAT THE  
ECMWF/UKMET SHOW A SLOWER PROGRESSION TO THE WAVE...HAVE A SURFACE  
LOW STRONGER AND FURTHER TO THE NORTHWEST...AND DONT DEAMPLIFY THE  
WAVE AS QUICKLY AS A NEW RIDGE EXPANDS IN THE EASTERN CONUS. THIS  
DOES LEAD TO SOME DIFFERENCE IN THE SENSIBLE WEATHER IMPACTS IN  
THE GREAT LAKES REGION. GIVEN THE STRONG SUPPORT FROM THE ECMWF  
ENSEMBLE MEMBERS FOR THE OPERATIONAL RUN...THIS SOLUTION CANNOT BE  
DISCOUNTED. HOWEVER...GIVEN THE CONSENSUS BETWEEN THE OTHER  
MODELS...THESE SHOULD BE ACCOUNTED FOR AS WELL. IN FACT...THE 00Z  
NAM AND 00Z GFS TRENDED A LITTLE FASTER WITH THE DEAMPLIFICATION  
OF THE WAVE ALOFT.  
 
TO TRY TO ACCOUNT FOR THESE TWO SOLUTIONS AS REASONABLY AS  
POSSIBLE...WILL RECOMMEND A BLEND OF THE 12Z ECMWF ENSEMBLE MEAN  
AND THE 00Z GFS. THE GFS TENDED TO BE STRONGER WITH THE WAVE THAN  
THE GEFS MEAN (OR CLOSER TO THE EURO CAMP)...WHILE THE ECMWF  
ENSEMBLE MEAN WAS MORE SUBDUED THAN THE OPERATIONAL RUN.  
 
CHANGES FROM PRELIMINARY PREFERENCE: NONE. THE ONLY MAJOR SHIFT IN  
THE 00Z MODEL CYCLE (WITHOUT THE ECMWF ENSEMBLE MEMBERS AVAILABLE  
YET) IS THAT THE UKMET HAS TRENDED TOWARD THE ECMWF SOLUTION.  
THEREFORE...THE PREVIOUS REASONING WAS HELD...WITH SOME MINOR  
TWEAKS TO THE LANGUAGE ABOVE TO ACCOUNT FOR THE NEW UKMET SOLUTION.  
 
...UPPER TROUGH DIGGING SOUTHEAST INTO THE PACIFIC NORTHWEST ON  
TUESDAY WITH LEE CYCLOGENESIS IN THE VICINITY OF MONTANA...   
..COLD FRONT CROSSING THE NW REACHING NRN PLAINS ON THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS / 00Z ECMWF / 00Z CMC  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 00Z NAM WAS CONSIDERABLY STRONGER WITH THE MID-LEVEL LOW OVER  
BRITISH COLUMBIA TONIGHT AS COMPARED TO THE OTHER MODELS.THIS LED  
TO SOME GROWING DIFFERENCES IN THE DAY 2-3 PERIOD OVER THE  
NORTHWEST. OTHER MODELS WERE IN BETTER AGREEMENT...ALTHOUGH THE  
00Z UKMET STILL HAS SOME DIFFERENT STRUCTURE TO THE OVERALL TROUGH  
AS IT DOES DIFFERENT THINGS WITH THE EMBEDDED SHORTWAVES. FOR  
EXAMPLE...THE LEAD SHORTWAVE IS MORE SHEARED OUT AND LIFTS  
NORTHEAST INTO MANITOBA FASTER THAN THE OTHER MODELS. THIS WAS A  
DIFFERENCE IN THE 12Z CYCLE AS WELL...ALTHOUGH IT DID TREND A BIT  
CLOSER TO THE OTHER MODELS. GIVEN THAT THE 00Z NAM AND 00Z UKMET  
ARE THE MORE NOTABLE OUTLIERS...THEY WERE NOT INCLUDED IN THE  
PREFERENCE FOR THIS SYSTEM...ALTHOUGH IT SHOULD BE NOTED THAT THE  
OVERALL DIFFERENCES ARE STILL FAIRLY SMALL.  
 
CHANGES FROM PRELIMINARY PREFERENCE: ADD CANADIAN MODEL. THE  
PRELIMINARY PREFERENCE WAS FOR A GFS/ECMWF BLEND...BUT THE CMC WAS  
INCLUDED IN THE FINAL PREFERENCE AS ITS 00Z RUN HAS COME INTO  
BETTER AGREEMENT WITH THE GFS AND ECMWF.  
 
   
..SHORTWAVE DROPPING SOUTH TOWARD THE PAC NW LATE THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS GENERALLY SHOW A SECONDARY SHORTWAVE DIGGING SOUTH THROUGH  
THE WESTERN PERIPHERY OF THE TROUGH...REINFORCING THE LONGWAVE  
TROUGH OVER THE WESTERN CONUS AND PERHAPS LEADING TO SOME  
ADDITIONAL SLIGHT AMPLIFICATION. THE 00Z ECMWF AND 00Z UKMET  
DEPICT THE STRONGER MID-LEVEL VORTICITY AND STRONGER MID-UPPER  
LEVEL JET WITH THIS WAVE...WHILE THE 00Z GFS...CMC...AND NAM ARE  
SLIGHTLY LESS VIGOROUS. THIS DOES SEEM TO LEAD TO A DIFFERENCE IN  
SENSIBLE WEATHER...WITH THE MODELS SHOWING A STRONGER WAVE  
GENERALLY ALSO BEING WETTER SOLUTIONS. WHILE THERE ARE STILL  
DIFFERENCES ON THE 00Z CYCLE...THEY ARE NOT SUBSTANTIALLY LARGE  
ENOUGH TO DISCOUNT EITHER WAY. THEREFORE...WILL RECOMMEND A  
GENERAL MODEL BLEND.  
 
CHANGES FROM PRELIMINARY PREFERENCE: CHANGE TO GENERAL BLEND. THE  
00Z MODELS HAVE COME INTO A LITTLE BETTER AGREEMENT. WITH NO  
OBVIOUS OUTLIERS (JUST NARROWING SPREAD IN SOLUTIONS)...A GENERAL  
BLEND IS RECOMMENDED.  
 
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