876  
FXUS10 KWNH 131702  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1201 PM EST MON NOV 13 2017  
 
VALID NOV 13/1200 UTC THRU NOV 17/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...UPPER LEVEL LOW DEVOLVING TO A SHORTWAVE AND EJECTING THROUGH  
THE PACIFIC NORTHWEST INTO SOUTHERN CANADA BY TUESDAY...  
...EASTWARD TROUGH PROGRESSION OVER THE GREAT LAKES  
WEDNESDAY...AND THE NORTHEAST BY THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z NAM / 00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
DIFFERENCES BEGIN TO APPEAR AS THE UPPER TROUGH NEARS THE N-CNTRL  
U.S. BY WED MORNING WITH SOME TIMING DIFFERENCES REGARDING TWO  
SMALLER WAVELENGTH SHORTWAVES WITHIN THE BROADER TROUGH AXIS  
TRANSLATING EAST. THE 00Z UKMET/CMC ARE ALSO FARTHER SOUTH WITH  
THE UPPER TROUGH WHICH IMPACTS SURFACE LOW PLACEMENT. AS THE  
TROUGH AXIS REACHES THE NORTHEAST...THE LATEST ENSEMBLES SHOW THE  
00Z UKMET/CMC AS NEAR OUTLIERS. THE 00Z UKMET IS A DEEPER OUTLIER  
WITH THE STRENGTH AND SOUTHWARD PLACEMENT OF STRONGER VORTICITY  
NEAR NEW ENGLAND...WHEREAS THE 00Z CMC IS WEAKER BUT ALSO A BIT  
SOUTH.  
 
A BLEND OF THE 12Z GFS/NAM AND 00Z ECMWF FITS WELL WITH THE LATEST  
ENSEMBLE CLUSTERING AND MEANS THROUGH THURSDAY WITH THIS SYSTEM.  
THE DIFFERENCE WITH THE 12Z GFS IS THAT IT SHOWS A STRONGER  
VORTICITY MAX OVER COASTAL NEW ENGLAND BY LATE THURSDAY WHICH IS  
SUPPORTED IN THE ENSEMBLES BUT THE GFS COULD BE TOO STRONG. A  
BLEND WITH THE WEAKER 12Z NAM OR 00Z ECMWF SHOULD TEMPER THE  
STRENGTH OF THIS FEATURE.  
 
...LEADING SHORTWAVE OF LONGWAVE TROUGH AXIS ALONG THE WEST COAST  
WED INTO THU...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 00Z UKMET  
CONFIDENCE: AVERAGE  
 
THE 12Z ECWMF STANDS OUT WITH THE LEADING EDGE OF THE TROUGH AXIS  
AS A NEAR OUTLIER WITH SHORTWAVE RIDGING BEHIND THE LEADING  
SHORTWAVE INTO SRN ALBERTA/SASKATCHEWAN THU MORNING AND THE  
REMAINING LARGER TROUGH AXIS JUST OFFSHORE OF THE WEST COAST. THE  
12Z NAM/GFS ARE SLOWER BUT MUCH MORE AMPLIFIED WITH THIS LEADING  
TROUGH AXIS THAN THE NON-NCEP MODELS...BUT A BLEND OF THE 12Z  
GFS/NAM AND 00Z UKMET SHOULD WORK WELL WITH THE LEADING EDGE OF  
THE TROUGH AXIS MOVING INLAND...AGREEING WELL WITH THE BETTER  
CLUSTERING OF ENSEMBLE MEMBERS...GIVEN THE 00Z UKMET IS DEFINED  
BUT NOT AS STRONG AS THE 12Z GFS OR 12Z NAM.  
 
...TRAILING LONGWAVE TROUGH AXIS PROGRESSING ACROSS THE WEST COAST  
ON THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM / 00Z ECMWF  
CONFIDENCE: BELOW AVERAGE  
 
THE ECMWF ENSEMBLE MEAN HAS BEEN CONSISTENT WITH A SLOWER TROUGH  
AXIS PROGRESSING ACROSS THE WEST COAST WHILE THE GEFS HAS BEEN  
CONSISTENTLY FASTER BY 00Z/17. WHILE THE 12Z GFS MATCHES THE  
GEFS...THE 00Z UKMET IS A SLOWER NEAR OUTLIER WITH ITS SLOWER  
PROGRESSION. GIVEN THE GFS HAS A KNOWN BIAS FOR PROGRESSING THESE  
TYPES OF SYSTEMS TOO QUICKLY TOWARD THE EAST AND THE ABUNDANCE OF  
ENSEMBLE GUIDANCE THAT IS SLOWER THAN THE GFS/GEFS...THE  
PREFERENCE IS TO BE SOMEWHERE IN THE MIDDLE. THE 00Z ECMWF MEAN IS  
FASTER THAN THE 00Z ECMWF...AND NEARER TO THE 12Z NAM. THE MIDDLE  
GROUND IS BEST REPRESENTED BY A 12Z NAM / 00Z ECMWF BLEND BUT  
CONFIDENCE IS BELOW AVERAGE GIVEN LARGER THAN AVERAGE SPREAD IN  
THE GUIDANCE.  
 
...TROUGH CROSSING OVER NEW ENGLAND TODAY WITH SURFACE LOW  
DEVELOPMENT WELL OFF THE EAST COAST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
   
..SHORTWAVE AMPLIFYING OVER THE NORTHEAST BY LATE TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
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