239  
FXUS10 KWNH 281651  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1150 AM EST TUE NOV 28 2017  
 
VALID NOV 28/1200 UTC THRU DEC 02/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...DEAMPLIFYING UPPER LEVEL TROUGH OVER THE EASTERN GULF OF MEXICO  
AND IN VICINITY OF FLORIDA...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 00Z CMC DEAMPLIFIES THE WAVE MORE RAPIDLY THAN THE OTHER  
AVAILABLE MODELS...AND ITS ENSEMBLE MEMBERS ALSO ALL HAVE HIGHER  
HEIGHT FIELDS ALOFT THROUGH THIS REGION THAN MOST OF THE OTHER  
OPERATIONAL MODELS OR ENSEMBLE MEMBERS. GIVEN THAT THIS SEEMS TO  
BE A CONSISTENT BIAS WITH THE MODEL...IT HAS BEEN EXCLUDED FROM  
THE PREFERENCE FOR THIS SYSTEM. THE OTHER MODELS SHOW SIMILARITY.  
 
...PROGRESSIVE TROUGH MOVING FROM UPPER MISSISSIPPI VALLEY THROUGH  
THE NORTHEAST BY WEDNESDAY EVENING...   
..ACCOMPANYING SURFACE LOW IN CANADA AND TRAILING COLD FRONT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
DESPITE SOME SMALL DETAIL DIFFERENCES...THE MODELS SHOW GOOD  
AGREEMENT WITH MANY OF THE MASS FIELDS ASSOCIATED WITH THIS  
SYSTEM. THE 00Z CMC AND 00Z UKMET SHOW SLIGHTLY HIGHER HEIGHTS  
THROUGH THE BASE OF THE TROUGH IN THE NORTHEAST...AND DEVIATE MORE  
FROM ENSEMBLE MEANS THAN THE OTHER MODELS. HOWEVER...DESPITE THESE  
POTENTIALLY BEING LESS LIKELY SOLUTIONS...THEY ARE CLOSE ENOUGH  
(REASONABLE POSSIBILITIES) TO BE INCLUDED FOR THIS SYSTEM.  
 
   
..MID-UPPER LEVEL LOW EXITING THE FOUR CORNERS TODAY
 
 
...DEVOLVING INTO AN OPEN WAVE AND DEAMPLIFYING AS IT PROGRESSES  
EAST TO THE CAROLINAS BY THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z NAM IS CLOSE TO THE OTHER MODELS IN ITS POSITION AND  
TIMING OF THE TROUGH AND ASSOCIATED MID-UPPER LEVEL VORT MAX.  
HOWEVER...IT DOES HAVE A STRONGER SYSTEM OVERALL (HIGHER VORTICITY  
VALUES, ETC.) AND THE SURFACE LOW AND TROUGH OVER THE SOUTHERN  
PLAINS ARE DISPLACED ABOUT 50-60MI NORTHEAST OF THE OTHER MODELS.  
FOR THIS REASON...PREFER A BLEND OF THE OTHER MODELS FOR THIS  
SYSTEM...WHICH OTHERWISE SHOW SIMILAR SOLUTIONS.  
 
...NORTHERN STREAM TROUGH MOVING INTO PACIFIC NORTHWEST  
TODAY...AND CROSSING NORTHERN TIER OF STATES THROUGH FRIDAY...   
..WEAK CYCLOGENESIS OVER THE CANADIAN PRAIRIES LATE WED
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF / 00Z CMC  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS SHOW GOOD SIMILARITY WITH THIS SYSTEM THROUGH THE FIRST  
36-48 HOURS OF THE FORECAST...WITH SOME DIVERGING SOLUTIONS  
THEREAFTER...PRIMARILY RELATED TO TIMING. THE 12Z NAM AND 00Z  
UKMET SHOW A SLIGHTLY SLOWER PROGRESSION OF THE TROUGH AXIS...WITH  
LOWER HEIGHTS ALOFT THROUGH THE OHIO RIVER VALLEY AND MID SOUTH  
FROM THURSDAY INTO EARLY FRIDAY. THE NAM IN PARTICULAR SHOWS A  
STRONGER SECONDARY WAVE TRAILING THROUGH THE BASE OF THE  
TROUGH...WHICH LIKELY LEADS TO THE LOWER HEIGHTS AND IMPACTS ON  
OTHER FIELDS IN THE MODEL. HOWEVER...THE 12Z GFS AND 00Z ECMWF/CMC  
ARE MUCH CLOSER TO THE ENSEMBLE MEANS AND FALL MORE CLEANLY WITHIN  
THE ENVELOPE OF ENSEMBLE MEMBER SPREAD. THEREFORE...THE PREFERENCE  
IS FOR A BLEND OF THESE THREE MODELS.  
 
...SOUTHERN STREAM WAVE DEVELOPING FROM APPROACHING PACIFIC TROUGH  
THROUGH WEDNESDAY...   
..EVOLVING CLOSED LOW AND SUBTROPICAL JET
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GEFS MEAN / 00Z ECMWF ENS MEAN  
CONFIDENCE: BELOW AVERAGE  
 
MODELS DIVERGE SUBSTANTIALLY WITH THIS SYSTEM...PARTICULARLY IN  
RELATION TO THE POSITION OF THE CLOSED LOW ALOFT AND OTHER MASS  
FIELDS IN THE MIDDLE TO UPPER TROPOSPHERE. DURING THIS PORTION OF  
THE FORECAST PERIOD (THROUGH FRIDAY)...THE IMPACTS ON SENSIBLE  
WEATHER MAY BE MORE LIMITED GIVEN A LACK OF QPF ON ANY MODEL  
SOLUTION ACROSS THE ENTIRE AREA UNDER AND NEAR THIS TROUGH. THERE  
IS QUITE A BIT OF SPREAD ON THE ENSEMBLES AS WELL...WITH A LACK OF  
CLEAR BIASES BASED ON MODEL TYPE. FOR EXAMPLE...THE GEFS HAS SOME  
MEMBERS WITH AN UPPER LEVEL LOW CLOSER TO THE DESERT  
SOUTHWEST...AND SOME AS FAR AS 1500MI AWAY WELL OVER THE PACIFIC  
OCEAN. GIVEN THE AMOUNT OF SPREAD AT THIS TIME...WILL PREFER A  
BLEND OF THE 12Z GEFS AND 00Z ECMWF ENSEMBLE MEAN MASS FIELDS.  
SOME MODELS (SUCH AS THE 00Z CMC AND UKMET) SHOW SEVERAL MID-UPPER  
LEVEL LOWS...BUT CONFIDENCE IS FAIRLY LOW IN THE PLACEMENT OF ANY  
OF THESE UNTIL MODELS BEGIN TO CLUSTER AROUND MORE COHERENT  
SOLUTIONS.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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