248  
FXUS10 KWNH 131853  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 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 MODEL EVALUATION WITH FINAL 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: 12Z GFS/ECMWF/CMC BLEND  
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 12Z UKMET REMAINS FARTHEST SOUTH OF THE  
DETERMINISTIC MODELS WITH THE BASE OF THE MEAN UPPER TROUGH AXIS  
WHICH IS STILL ON THE DEEPER SIDE WITH RESPECT THE  
LATEST...00Z/13...ENSEMBLE GUIDANCE. THE 12Z ECMWF TRENDED DEEPER  
COMPARED TO ITS 00Z RUN BUT IS WITHIN REASON...ALONG WITH THE 12Z  
CMC GIVEN IT TRENDED DEEPER THAN ITS PREVIOUSLY WEAKER 00Z CYCLE.  
 
THE ENSEMBLE MEANS SUPPORT A 12Z NAM/GFS/ECMWF BLEND WITH THE  
PRIMARY SURFACE LOW TRACKING ACROSS SRN CANADA THROUGH THU.  
HOWEVER...THE 12Z NAM IS FASTER WITH THE ENERGY IN THE BASE OF THE  
TROUGH SWEEPING ACROSS LAKES ERIE AND ONTARIO...WHICH RESULTS IN  
LESS OF A SURFACE REFLECTION ALONG THE NEW ENGLAND COAST BY THU  
EVENING...WITH A NON 12Z NAM CONSENSUS SUPPORTING MORE DEVELOPMENT  
BY 00Z/17.  
 
OVERALL...A 12Z GFS/ECMWF/CMC BLEND WORKS FOR THIS SYSTEM WITH THE  
12Z CMC WEAKEST OF THE THREE MODELS. THE 12Z UKMET IS THOUGHT TO  
BE TOO STRONG WITH ITS SURFACE LOW NEAR NEW ENGLAND BY LATE THU.  
 
...LEADING SHORTWAVE OF LONGWAVE TROUGH AXIS ALONG THE WEST COAST  
WED INTO THU...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z UKMET  
CONFIDENCE: AVERAGE  
 
THE 00Z 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 BUT  
THE 12Z ECMWF APPEARS TO HAVE STARTED A POSSIBLE TREND TO BE MORE  
SIMILAR TO THE NON ECMWF GUIDANCE HERE. 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 12Z UKMET  
SHOULD WORK WELL WITH THE LEADING EDGE OF THE TROUGH AXIS MOVING  
INLAND...AGREEING WELL WITH THE BETTER CLUSTERING OF ENSEMBLE  
MEMBERS. THE 12Z UKMET TRENDED DEEPER BUT IS A LITTLE SLOWER THAN  
THE 12Z NAM/GFS BY 00Z/17. THE 12Z CMC APPEARS TOWARD THE FASTER  
SIDE OF THE MODELS AND IS CONSIDERED UNLIKELY.  
 
...TRAILING LONGWAVE TROUGH AXIS PROGRESSING ACROSS THE WEST COAST  
ON THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM / 00Z ECMWF / 12Z UKMET  
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.  
 
19Z UPDATE: THE 12Z ECMWF/CMC TRENDED SLOWER BY 00Z/17 ALONG THE  
WEST COAST COMPARED TO THEIR 00Z CYCLES AND THE 12Z UKMET TRENDED  
FASTER. GIVEN THEIR CURRENT PLACEMENT WITH RESPECT TO THE  
PREFERRED MIDDLE GROUND MENTIONED IN THE PREVIOUS PARAGRAPH...THE  
12Z NAM...00Z ECMWF AND 12Z UKMET APPEAR TO BE THE BEST FIT TO  
THIS IDEA WHEREAS THE 12Z ECMWF AND 12Z CMC ARE CONSIDERED TOO  
SLOW. CONFIDENCE REMAINS BELOW AVERAGE.  
 
...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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