592  
FXUS10 KWNH 261658  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1157 AM 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 NAM/GFS EVALUATION...WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...BROAD UPPER TROUGHING OVER THE EASTERN GULF OF MEXICO THROUGH  
TUE NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WHILE DIFFERENCES ARE NOT TREMENDOUS...THE 00Z UKMET CONTINUES TO  
LOOK DIFFERENT WITH ITS HANDLING OF THE 500 MB PATTERN COMPARED TO  
THE OTHER MODELS ACROSS THE SOUTHEAST U.S...SO A NON 00Z UKMET  
BLEND IS PREFERRED.  
 
   
..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: BLEND OF THE 12Z GFS/00Z ECMWF/00Z UKMET  
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. DIFFERENCES  
IN THE LATEST GUIDANCE ARE RELATIVELY MINOR BUT A 12Z GFS/00Z  
ECMWF/00Z UKMET BLEND APPEARED BEST FOR THIS SYSTEM GIVEN  
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: 00Z ECMWF/12Z 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 00Z ECMWF AND 12Z NAM APPEAR THE BEST COMPROMISE HERE  
GIVEN THEIR SIMILAR AND IN-THE-MIDDLE-TIMING WITH THE 00Z UKMET  
SLIGHTLY SLOWER THAN THE 00Z ECMWF/12Z NAM AND 00Z CMC EVEN SLOWER  
THAN THE 00Z UKMET. GIVEN SOME OF THE ENSEMBLE TRENDS TO BE  
QUICKER...DO NOT WANT TO GO TOWARD THE SLOWEST GUIDANCE...WITH THE  
MIDDLE GROUND 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/00Z UKMET BLEND  
CONFIDENCE: AVERAGE  
 
TIMING AND AMPLITUDE DIFFERENCES BEGIN RATHER EARLY WITH THIS  
SYSTEM AS THE UPPER TROUGH NEARS THE PACIFIC NORTHWEST MON NIGHT.  
THE 12Z NAM/GFS ARE INITIALLY A LITTLE FASTER THAN THE REMAINING  
MODELS BUT THE 00Z UKMET CATCHES UP. THE 00Z ECMWF/CMC ARE SLOWER  
WITH THE CMC SLOWEST. THE 00Z ECMWF ALSO APPEARS FLATTER COMPARED  
TO THE REMAINING DETERMINISTIC AND AVAILABLE ENSEMBLE MEMBERS. THE  
12Z NAM...12Z GFS AND 00Z UKMET APPEAR MOST SIMILAR BUT THE 12Z  
NAM APPEARS TOWARD THE DEEPER SIDE OF THE LATEST ENSEMBLE GUIDANCE  
BY 00Z/30 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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