283  
FXUS10 KWNH 291647  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1147 AM 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 NAM/GFS EVALUATION ALONG WITH PRELIMINARY 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/00Z ECMWF/00Z UKMET BLEND THROUGH 00Z/01  
12Z GFS/00Z ECMWF BLEND 00Z/01 - 00Z/02  
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 ALONG THE GULF COAST. THE 12Z GFS IS A BIT  
SOUTHWEST AND THE 00Z ECMWF MORE TO THE NORTH. ENSEMBLE MEANS SHOW  
DECENT AGREEMENT WITH THIS FEATURE WHICH REPRESENTS A BLEND  
BETWEEN THE 12Z GFS...00Z ECMWF AND 00Z UKMET THROUGH ABOUT  
00Z/01. BEYOND 00Z/01...THE 00Z UKMET BECOMES A BIT STRONGER AS  
THE LOW REACHES THE EASTERN GULF AND A 50/50 12Z GFS/00Z ECMWF  
BLEND IS PREFERRED.  
 
...SECOND MID-LEVEL SHORTWAVE PROGGED TO REACH THE NORTHERN  
ROCKIES LATE SUN INTO MON...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS...00Z ECMWF AND 00Z UKMET  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ENSEMBLE DATA SUPPORTS A NON 00Z UKMET BLEND GIVEN IT LIES ON THE  
FAR EDGE OF THE ENSEMBLE SPAGHETTI HEIGHT PLOTS. THE 12Z NAM IS  
CONSIDERED A FLATTER SOLUTION WITH BETTER AGREEMENT SEEN TOWARD  
THE 12Z GFS...00Z ECMWF AND 00Z UKMET.  
 
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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