484  
FXUS10 KWNH 281853  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 PM 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 MODEL EVALUATION ALONG WITH FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...DEAMPLIFYING MID-LEVEL VORTICITY MAX REACHING SOUTHERN BRITISH  
COLUMBIA TODAY AND SHEARING SOUTHEASTWARD WITH TIME...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
COMPARED TO ITS 00Z RUN...THE 12Z CMC ADJUSTED MORE IN LINE WITH  
THE REMAINING DETERMINISTIC CONCERNING A MORE DEFINED VORTICITY  
MAX AS THE REMNANT SYSTEM CROSSES THE MIDWEST LATE FRI AND TOWARD  
THE NORTHEAST COAST EARLY SAT. SINCE YESTERDAY...THERE HAS BEEN A  
TREND TOWARD A MORE DEFINED VORTICITY MAX OVER THE EASTERN U.S.  
COMPARED TO YESTERDAY. GIVEN DECENT AGREEMENT IN THE 12Z  
GUIDANCE...A GENERAL MODEL 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: NON 12Z UKMET BLEND  
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 12Z UKMET  
TRENDED LESS PROGRESSIVE WITH THE UPPER TROUGH WHICH APPEARS TO BE  
A GOOD MOVE CONSIDERING AGREEMENT FROM THE REMAINING MODELS BUT  
THE 12Z UKMET IS A BIT STRONG COMPARED TO THE REMAINING GUIDANCE.  
REGARDING POSITION...THE 12Z UKMET IS A LITTLE CLOSER TO THE  
COAST...AND CONSIDERING IT IS ALSO STRONGER...A NON 12Z UKMET  
BLEND SHOWS MORE SUPPORT FOR THIS SYSTEM GIVEN GOOD AGREEMENT TO  
THE LATEST ENSEMBLE GUIDANCE.  
 
...ROBUST PACIFIC SHORTWAVE IMPACTING THE NORTHWEST FRI INTO SAT  
WITH ATTENDANT SURFACE FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/12Z 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  
12Z 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 12Z 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 AND THE 12Z GFS IS FARTHER WEST  
WITH THE FRONTAL BOUNDARY/SURFACE LOW COMPARED TO THE REMAINING  
GUIDANCE. GIVEN SIMILAR UPPER TROUGH PLACEMENT ACROSS NORTHERN MX  
AT THIS TIME...A BLEND OF THE FASTER 12Z ECMWF AND SLOWER 12Z GFS  
PREFERRED WITH REDUCED CONFIDENCE.  
 
...SECOND MID-LEVEL SHORTWAVE PROGGED TO REACH THE NORTHERN  
ROCKIES SUN EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z NAM BLEND  
CONFIDENCE: AVERAGE  
 
ENSEMBLE DATA SUPPORTS A BLEND CLOSEST TO A NON 12Z NAM  
BLEND...WITH THE 12Z NAM A BIT FASTER/WEAKER WITH THE SYSTEM AS IT  
APPROACHES THE ID PANHANDLE AND MT ON SUN.  
 
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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