362  
FXUS10 KWNH 291833  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
133 PM EST FRI DEC 29 2017  
 
VALID DEC 29/1200 UTC THRU JAN 02/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...EXITING NEGATIVELY TILTED MID-LEVEL TROUGH CURRENTLY OVER THE  
NORTHEAST THIS MORNING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
...CLOSED MID-LEVEL LOW CENTERED OVER SOUTHERN ONTARIO/QUEBEC ON  
SAT MORNING...REACHING NORTHERN NEW ENGLAND SAT NIGHT...  
...INDUCED SURFACE CYCLOGENESIS OFF OF THE NEW ENGLAND COAST LATE  
SAT WITH ACCOMPANYING TROUGH AXIS EXTENDING TO THE NEW ENGLAND  
COAST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
...ROBUST PACIFIC SHORTWAVE IMPACTING THE NORTHWEST FRI INTO SAT  
WITH ATTENDANT SURFACE FRONT...  
...WEAKENING SHORTWAVE TRACKING FROM THE NORTHWEST ON SAT TO THE  
MS VALLEY ON SUN...   
..FRONTAL WAVE NEAR THE CNTRL GULF COAST ON SUN
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
TIMING OF THE WEAKENING UPPER TROUGH APPEARS REASONABLE IN THE  
LATEST MODELS GIVEN ONLY MINOR DIFFERENCES WERE NOTED. THE BIGGEST  
DIFFERENCES ARE NOTED ALONG THE GULF COAST WHERE THE 12Z NAM IS  
STRONGER ALOFT AND AT THE SURFACE RESULTING IN A SURFACE WAVE  
LOCATED FARTHER EAST THAN THE REMAINING DETERMINISTIC GUIDANCE  
THROUGH SUNDAY NIGHT. THE 12Z GFS IS A BIT SOUTHWEST AND THE 12Z  
ECMWF MORE TO THE NORTH BUT IN THE MIDDLE OF THE MODEL SPREAD.  
ENSEMBLE MEANS SHOW DECENT AGREEMENT WITH THIS FEATURE WHICH  
REPRESENTS A BLEND BETWEEN THE 12Z GFS/ECMWF/UKMET. THE 12Z UKMET  
REMAINS A BIT STRONG COMPARED TO THE REMAINING GUI9DANCE BUT IT  
DID TREND SOUTH A BIT FROM ITS 00Z RUN AND HAS BEEN INCLUDED IN  
THE PREFERRED BLEND THROUGH F084 HOURS OR 00Z/02.  
 
...SECOND MID-LEVEL SHORTWAVE PROGGED TO REACH THE NORTHERN  
ROCKIES LATE SUN INTO MON...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/ECMWF/UKMET  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ENSEMBLE DATA SUPPORTS A 12Z GFS/ECMWF/UKMET BLEND GIVEN IT SHOWS  
BETTER AGREEMENT TO THE LATEST ENSEMBLE SPAGHETTI HEIGHT PLOTS.  
THE 12Z NAM AND 12Z CMC ARE CONSIDERED TOO FLAT ALTHOUGH  
DIFFERENCES ARE NOT VERY LARGE THROUGH MON.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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