785  
FXUS10 KWNH 291712  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1211 PM EST WED NOV 29 2017  
 
VALID NOV 29/1200 UTC THRU DEC 03/0000 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 CONTINUED TO SHOW A HIGH HEIGHT BIAS IN AND AROUND THE  
DEAMPLIFYING TROUGH...WHICH WAS A CONSISTENT BIAS THROUGH THE CMC  
ENSEMBLE MEMBERS AS WELL. THERE IS A LACK OF SUPPORT FOR THIS FROM  
OTHER MODELS...SO THE CMC IS EXCLUDED FROM THE PREFERENCE FOR THIS  
SYSTEM. OTHER MODELS SHOWED VERY GOOD AGREEMENT WITH THE MASS  
FIELDS FOR THIS SYSTEM.  
 
   
..PROGRESSIVE TROUGH EXITING THE NORTHEAST TODAY
 
   
..OCCLUDING LOW NEAR THE LABRADOR SEA AND TRAILING COLD FRONT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS SHOW A GREAT DEGREE OF SIMILARITY WITH THIS SYSTEM...AND A  
GENERAL MODEL BLEND IS PREFERRED FOR THAT REASON.  
 
   
..SHORTWAVE ACCELERATING TO THE COASTAL CAROLINAS BY THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS SHOW SIMILARITY WITH THIS SYSTEM. THE 00Z CMC HAS MID-UPPER  
LEVEL HEIGHTS THAT ARE SLIGHTLY HIGHER...BUT THE BIAS IS NOT AS  
NOTABLE AS WITH THE DEAMPLIFYING TROUGH NEAR FLORIDA. THE 12Z NAM  
HAS MID-UPPER LEVEL HEIGHTS THAT ARE SLIGHTLY LOWER...BUT AGAIN  
THE BIAS IS NOT TOO LARGE. ADDITIONALLY...THE SHORTWAVE BECOMES  
DISASSOCIATED WITH PRECIPITATION POTENTIAL WITH TIME...SO MINOR  
MODEL DIFFERENCES SHOULD NOT HAVE A LARGE IMPACT ON SENSIBLE  
WEATHER. THEREFORE...A GENERAL MODEL BLEND IS PREFERRED WITH THIS  
SYSTEM.  
 
   
..NORTHERN STREAM TROUGH EXITING NORTHERN ROCKIES TODAY
 
AND  
CROSSING NORTHERN TIER OF STATES THROUGH FRIDAY NIGHT...   
..CONTINUED WEAK CYCLOGENESIS INTO ONTARIO THROUGH THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: THROUGH 01/00Z - GENERAL MODEL BLEND  
AFTERWARD - BLEND OF 00Z ECMWF / 00Z CMC  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THERE IS GOOD AGREEMENT IN THE MASS FIELDS AMONG THE MODELS  
THROUGH THE FIRST 36 HOURS OF THE FORECAST. DIFFERENCES BEGIN TO  
EMERGE AFTER THAT POINT RELATED TO THE AMPLIFICATION OF THE TROUGH  
AS IT REACHES THE EAST COAST. THE 12Z NAM AND GFS BOTH SHOW THE  
WAVE MAKING MORE PROGRESS EAST BY 03/00Z...WHILE THE 00Z ECMWF/CMC  
SHOW SLIGHTLY LESS PROGRESS AND THE 00Z UKMET MUCH SLOWER. ALL  
MODELS SHOW SOME DEGREE OF CYCLOGENESIS OFFSHORE ASSOCIATED WITH  
WAVE AMPLIFICATION. THE USUAL EXPECTATION IN THESE SCENARIOS WOULD  
BE FOR THE ASSOCIATED WAVE ALOFT TO BEGIN TO SLOW...AND FOR THIS  
REASON WILL EXCLUDE THE FASTEST SOLUTIONS ON THE TABLE AT THIS  
TIME (NAM/GFS). THE 00Z UKMET IS A SLOW OUTLIER...AND DOES NOT  
HAVE AS MUCH ENSEMBLE SUPPORT. FOR THIS REASON...THE PREFERENCE  
AFTER 36 HOURS WILL LEAN TOWARD A BLEND OF THE ECMWF AND CMC. THE  
12Z GFS DID SHOW SLIGHTLY SLOWER PROGRESSION TO THE TROUGH AS  
COMPARED TO ITS 06Z RUN...AND IN THE BASE OF THE TROUGH IT WAS  
SLOWER AS COMPARED TO ITS 12Z RUN 24 HOURS AGO. THESE TRENDS ALSO  
SUPPORT A GREATER WEIGHT TO SLOWER TROUGH PROGRESSION.  
 
...ELONGATING SOUTHERN STREAM TROUGH AND DEVELOPING CLOSED LOW  
NEAR NORTHERN BAJA CALIFORNIA BY FRIDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z ECMWF / 00Z ECMWF ENS MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
ALTHOUGH THERE IS STILL A FAIR AMOUNT OF MODEL SPREAD WITH THE  
POSITIONING OF THE MID-UPPER LEVEL LOW NEAR BAJA CALIFORNIA...THE  
SPREAD HAS DIMINISHED CONSIDERABLY OVER THE PAST SEVERAL MODEL  
CYCLES. BY 01/00Z THERE IS QUITE A BIT OF OVERLAP BETWEEN THE LOW  
POSITIONS FROM ALL THE AVAILABLE MODELS. THE 00Z CMC IS SHOWING  
ITS HIGH HEIGHT BIAS AGAIN AT LOWER LATITUDES WITH THIS SYSTEM  
THROUGH MUCH OF THE TROUGH. THE 12Z NAM AND 00Z  
UKMET...HOWEVER...SEEM TO SHOW A STRONGER LOW EVOLVING. THE 12Z  
NAM HAS THE LOWEST HEIGHTS AT THE CENTER OF THE LOW OVERALL AMONG  
AVAILABLE MODELS...AND THE 00Z UKMET SHOWS A BROADER EXTENT OF LOW  
HEIGHTS THAN OTHER AVAILABLE MODELS. THE 12Z GFS SHOWS A FASTER  
PROGRESSION OF THE LOW INTO THE BAJA CALIFORNIA REGION...WITH A  
MUCH STRONGER SECONDARY LOW FURTHER SOUTHWEST OVER THE PACIFIC.  
THERE IS LIMITED MODEL SUPPORT FOR THE STRENGTH OF THE SECONDARY  
LOW...AND ONLY THE 00Z CMC SHOWS AS FAST A PROGRESSION INTO THE  
PACIFIC COAST WITH THE PRIMARY LOW. FOR THESE REASONS...PREFER TO  
LEAN TOWARD THE MORE CONSISTENT 00Z ECMWF ENSEMBLE MEAN...WHICH  
HAS SHOWN A SIMILAR POSITION OF THE LOW OVER THE PAST COUPLE MODEL  
CYCLES AND REPRESENTS A COMPROMISE OF THE INTENSITY AND  
PROGRESSION OF THE LOW ALOFT. THE 00Z OPERATIONAL ECMWF IS FAIRLY  
CLOSE TO THIS...SO IT IS INCLUDED IN THE PREFERENCE AS WELL.  
 
...LOW AMPLITUDE SHORTWAVE REACHING THE PACIFIC NORTHWEST THURSDAY  
AND PROGRESSING NEAR US-CANADA BORDER THROUGH SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
THERE ARE DETAIL DIFFERENCES WITH THIS SYSTEM...PRIMARILY RELATED  
TO THE AMPLIFICATION AND STRENGTH OF THE WAVE. THE 00Z ECMWF/CMC  
AND 12Z NAM TEND TO SHOW SLIGHTLY MORE AMPLIFICATION WITH THE 12Z  
GFS AND 00Z UKMET SHOWING A FLATTER AND WEAKER WAVE. HOWEVER...THE  
MASS FIELDS ARE CLOSE ENOUGH THAT A GENERAL BLEND IS PREFERRED FOR  
NOW...AND THE IMPACTS ON SENSIBLE WEATHER SHOULD BE RELATIVELY  
MINOR.  
 
   
..GULF OF ALASKA TROUGH DIGGING INTO PACIFIC NORTHWEST BY SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND THAT INCORPORATES ECMWF ENS MEAN  
CONFIDENCE: AVERAGE  
 
THE 12Z NAM IS FASTER WITH THE PROGRESSION OF THIS WAVE THAN THE  
OTHER MODELS AND MOST ENSEMBLE MEMBERS. THE OPERATIONAL RUNS OF  
THE GLOBAL MODELS APPEAR TO GENERALLY SHOW GOOD AGREEMENT ON THE  
TIMING AND OVERALL AMPLITUDE. THEREFORE...A GENERAL MODEL BLEND IS  
RECOMMENDED AT THIS TIME. HOWEVER...MANY OF THE OPERATIONAL RUNS  
SHOW CONSIDERABLY LOWER HEIGHTS IN THE CORE OF THE TROUGH  
(AFFECTING WA/OR) THAN THE 00Z ECMWF ENSEMBLE MEAN...SUGGESTING A  
HIGHER PROBABILITY OF A WEAKER WAVE THAN MAY BE INDICATED BY JUST  
LOOKING AT THE OPERATIONAL MODEL RUNS. THEREFORE...PREFER A  
GENERAL BLEND THAT INCORPORATES THE ECMWF ENS MEAN TO ACCOUNT FOR  
THIS POSSIBILITY.  
 
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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