474  
FXUS10 KWNH 261846  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
146 PM EST SUN NOV 26 2017  
 
VALID NOV 26/1200 UTC THRU NOV 30/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...BROAD UPPER TROUGHING OVER THE EASTERN GULF OF MEXICO THROUGH  
TUE NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/GFS/ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WHILE DIFFERENCES ARE NOT TREMENDOUS...THE 12Z UKMET AND 12Z CMC  
ARE A BIT STRONGER AND DISPLACED WITH ONE OR TWO MAIN VORTICITY  
CENTERS COMPARED TO THE 12Z NAM/GFS/ECMWF AND THE LATEST ENSEMBLE  
MEANS.  
 
   
..UPPER TROUGH CROSSING THE NORTHEAST U.S. EARLY MON
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
...DEEP UPPER TROUGH OFFSHORE THE WEST COAST SPLITTING WITH  
.NORTHERN STREAM TROUGH AXIS AND ASSOCIATED SURFACE LOW/COLD FRONT  
TRACKING ACROSS SOUTHERN CANADA FROM MON TO WED...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NEAR THE 12Z GFS  
CONFIDENCE: AVERAGE  
 
THE 12Z NAM WAS MORE WRAPPED UP/STRONGER WITH THE MID-LEVEL  
REFLECTION OF THIS SYSTEM AS IT TRACKED INTO MANITOBA WHICH  
AFFECTED THE TIMING OF THE RELATED SURFACE COLD FRONT. THE 12Z  
UKMET WAS A BIT FASTER...12Z CMC DISPLACED SOUTH WITH THE CORE OF  
THE UPPER TROUGH ALOFT AND THE 12Z ECMWF A TAD SLOWER WITH THE  
TROUGH PROGRESSION INTO THE NORTHEAST. THE 12Z GFS APPEARS TO BE  
THE BEST MIDDLE GROUND GIVEN ITS AGREEMENT TO A MAJORITY OF THE  
LATEST ENSEMBLE GUIDANCE.  
 
...SOUTHERN STREAM TROUGH AXIS/CLOSED LOW INTO THE SOUTHWEST MON  
AND INTO THE SOUTHERN PLAINS LATE TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/UKMET/NAM BLEND  
CONFIDENCE: AVERAGE  
 
THE ENSEMBLE SPREAD IS RATHER LARGE WITH THIS SYSTEM AND THE GEFS  
MEMBERS HAVE TRENDED MUCH FASTER SINCE YESTERDAY.  
HOWEVER...SMALLER CHANGES WERE SEEN IN THE REMAINING MODELS WHICH  
MAKES THE GEFS AND THE SIMILAR 12Z GFS APPEAR TOO QUICK AND TOO  
WEAK WITH THE 500 MB REFLECTION OF THIS SYSTEM AS IT REACHES THE  
PLAINS. THE 12Z ECMWF/UKMET/NAM APPEARS TO BE THE BEST COMPROMISE  
HERE GIVEN THEIR SIMILAR AND IN-THE-MIDDLE-TIMING WITH THE 12Z CMC  
CONTINUING TO BE SLOWER. GIVEN SOME OF THE ENSEMBLE TRENDS TO BE  
QUICKER...DO NOT WANT TO GO TOWARD THE SLOWEST GUIDANCE...WITH THE  
MIDDLE GROUND AND MODE APPEARING BEST.  
 
...POSITIVELY TILTED UPPER TROUGH AXIS AND ASSOCIATED COLD FRONT  
IMPACTING THE WEST COAST ON TUE AND REACHING THE CENTRAL/NORTHERN  
PLAINS ON WED...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS/12Z UKMET/12Z CMC BLEND  
CONFIDENCE: AVERAGE  
 
MODEL CONVERGENCE WAS SEEN WITH THE 12Z GUIDANCE RESOLVING EARLIER  
TIMING AND AMPLITUDE DIFFERENCES WITH THIS SYSTEM UNTIL IT MOVES  
INLAND FOR WED. THE 12Z ECMWF STANDS OUT THE GREATEST WITH A LESS  
AMPLIFIED TROUGH AND A FASTER PROGRESSION INTO THE PLAINS. THE  
ENSEMBLES SUPPORT A TIMING CLOSER TO THE 12Z UKMET/CMC AND  
SOMEWHAT SLOWER 12Z GFS THROUGH 00Z/30 WITH THIS SYSTEM. THE NAM  
APPEARS SIMILAR TO THESE MODELS AS WELL UNTIL 00Z/30 WHEN IT LEANS  
TOWARD THE DEEPER SIDE OF THE LATEST AVAILABLE ENSEMBLE  
GUIDANCE...WHICH LEAVES THE 12Z NAM OUT OF THE PREFERENCE.  
 
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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