088  
FXUS10 KWNH 281656  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 AM EST THU DEC 28 2017  
 
VALID DEC 28/1200 UTC THRU JAN 01/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...DEAMPLIFYING MID-LEVEL VORTICITY MAX REACHING SOUTHERN BRITISH  
COLUMBIA TODAY AND SHEARING SOUTHEASTWARD WITH TIME...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 00Z CMC IS THE ONLY DETERMINISTIC MODEL TO WEAKEN THE  
VORTICITY MAX QUICKLY AFTER MAKING LANDFALL INTO BRITISH COLUMBIA  
TONIGHT...WITH THE REMAINING GUIDANCE STILL SHOWING A MORE DEFINED  
FEATURE AS THE REMNANT SYSTEM CROSSES THE MIDWEST LATE FRI AND  
TOWARD THE NORTHEAST COAST EARLY SAT. THERE HAS BEEN A TREND  
TOWARD A MORE DEFINED VORTICITY MAX OVER THE EASTERN U.S. COMPARED  
TO YESTERDAY. GIVEN DECENT AGREEMENT OUTSIDE OF THE WEAKER 00Z  
CMC...A NON 00Z CMC BLEND IS RECOMMENDED.  
 
...NEGATIVELY TILTED MID-LEVEL TROUGH CROSSING THE UPPER MS VALLEY  
TODAY AND REACHING THE NORTHEAST ON FRI...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
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: BLEND OF THE 12Z NAM...12Z GFS AND 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
TRENDS IN THE ENSEMBLE SCATTER LOW PLOTS HAVE SHOWN A WESTWARD  
MOVEMENT OVER THE PAST FOUR 12/00Z CYCLES VALID 00Z/31 REGARDING A  
SURFACE LOW LOCATED EAST OF THE MID-ATLANTIC COAST. THE 00Z UKMET  
IS THE MOST PROGRESSIVE WITH THE UPPER TROUGH WHICH APPEARS  
CONTRARY TO TRENDS AND THE 00Z CMC IS STRONGEST WITH THE SURFACE  
LOW...A BIT DEEPER THAN THE LATEST ENSEMBLE MEANS. A BLEND OF THE  
12Z NAM...12Z GFS AND 00Z ECMWF APPEARS BEST FOR THIS SYSTEM WITH  
THE BEST AGREEMENT TO EACH OTHER AND THE ENSEMBLE MEAN DATA.  
 
...ROBUST PACIFIC SHORTWAVE IMPACTING THE NORTHWEST FRI INTO SAT  
WITH ATTENDANT SURFACE FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/00Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
OVERALL MODEL TRENDS HAVE BEEN FASTER WITH THE POSITIVELY TILTED  
TROUGH AXIS AS IT CROSSES THE MS RIVER VALLEY ON SUN.  
CURRENTLY...THE 12Z NAM/GFS ARE FASTER WITH THIS SYSTEM WHILE THE  
00Z ECMWF/UKMET/CMC ARE SLOWER. THE ENSEMBLE MEANS ARE IN THE  
MIDDLE...WHICH IS WHERE THE PREFERENCE LEANS. A BLEND OF THE 12Z  
GFS AND 00Z ECMWF ARE CLOSEST TO THE PLACEMENT OF THE GEFS/EC  
MEANS WITH THIS SYSTEM.  
 
REGARDING THE PLACEMENT OF A FRONTAL BOUNDARY NEAR THE GULF COAST  
AND POSSIBLE SURFACE LOW FOR SUN...THE 12Z NAM IS UNSUPPORTED WITH  
ITS FRONTAL LOW/BOUNDARY PLACEMENT WITH A BLEND OF THE STRONGER  
00Z ECMWF AND WEAKER 12Z GFS PREFERRED.  
 
...SECOND MID-LEVEL SHORTWAVE PROGGED TO REACH THE NORTHERN  
ROCKIES SUN EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS...00Z ECMWF AND 00Z UKMET  
CONFIDENCE: AVERAGE  
 
ENSEMBLE DATA SUPPORTS A BLEND CLOSEST TO THE 12Z GFS...00Z ECMWF  
AND 00Z UKMET WITH THE 12Z NAM FASTER/WEAKER AND THE 00Z CMC  
WEAKER AS THE SYSTEM APPROACHES THE ID PANHANDLE AND MT.  
 
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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