969  
FXUS10 KWNH 100436  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1235 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 PRELIMINARY 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  
12Z ECMWF AND MANY OF ITS ENSEMBLE MEMBERS WHICH CONTINUE TO SHOW  
A STRONGER VORT MAX AT THE CORE OF THE TROUGH -AND- (2) MOST OF  
THE REMAINING OPERATIONAL MODELS. DIFFERENCES ARE NOT SUBSTANTIAL  
IN THE MASS FIELDS THROUGH THE FIRST 24-36 HOURS...BUT AFTER THAT  
THE ECMWF SHOWS A SLOWER PROGRESSION TO THE WAVE...HAS ITS SURFACE  
LOW STRONGER AND FURTHER TO THE NORTHWEST...AND DOESN'T 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.  
 
...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 / 12Z ECMWF  
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...WHEREAS  
THE 12Z CMC WAS NOTABLY WEAKER. THESE LED TO SOME GROWING  
DIFFERENCES IN THE DAY 2-3 PERIOD OVER THE NORTHWEST. OTHER MODELS  
WERE CLOSER...ALTHOUGH THE 12Z UKMET LIFTED THE LEAD SHORTWAVE  
FASTER TO THE EAST-NORTHEAST OVER SOUTHERN CANADA (THE CANADIAN  
DID THIS TOO ALBEIT TO A LESSER EXTENT). THE 00Z GFS WAS  
RELATIVELY CLOSE TO THE 12Z GFS AND BOTH WERE FAIRLY  
REPRESENTATIVE OF MODEL CONSENSUS (CLOSE TO THEIR ENSEMBLE MEANS  
AS WELL)...THEREFORE A BLEND OF THE TWO IS RECOMMENDED.  
 
   
..SHORTWAVE DROPPING SOUTH TOWARD THE PAC NW LATE THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GFS / 12Z ECMWF  
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 LARGEST OUTLIER WITH THIS  
SYSTEM WAS THE 12Z UKMET WHICH SHOWED A SIGNIFICANTLY STRONGER AND  
SLOWER WAVE THAN THE OTHER MODELS. SMALLER DIFFERENCES EXISTED  
OTHERWISE...WITH THE PRIMARY DIFFERENCE APPEARING TO BE TIMING  
BETWEEN THE SLOWER 00Z GFS AND 12Z ECMWF...AND FASTER 00Z NAM AND  
12Z CMC. PREFER A BLEND OF THE 00Z GFS AND 12Z ECMWF AS THE NAM  
HAS HAD LESS RUN-TO-RUN CONSISTENCY WITH THE TIMING.  
 
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