176  
FXUS10 KWNH 291853  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
152 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 FINAL 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.  
 
18Z UPDATE: NO CHANGE TO PRELIMINARY PREFERENCE. THE 12Z CMC HAS  
MOVED A LITTLE CLOSER TO OTHER MODELS AT SOME LEVELS...BUT AT  
OTHERS REMAINS A CLEAR OUTLIER. FOR INSTANCE...AT 250MB IT SHOWS A  
RIDGE NEAR 67W BY 01/00Z...WHILE ALL THE OTHER MODELS SHOW A  
SUBTLE TROUGH REMAINING. FOR THIS REASON...THE CMC IS EXCLUDED  
FROM THE PREFERENCE.  
 
   
..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 SIMILARITY WITH THIS SYSTEM...AND A GENERAL MODEL  
BLEND IS PREFERRED FOR THAT REASON.  
 
18Z UPDATE: NO CHANGE TO PRELIMINARY PREFERENCE.  
 
   
..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.  
 
18Z UPDATE: NO CHANGE TO PRELIMINARY PREFERENCE OR REASONING.=  
 
   
..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 12Z ECMWF / 12Z GFS  
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.  
 
18Z UPDATE: CHANGE OF THE BLEND AFTER 36 HOURS. THE 12Z GLOBAL  
MODELS HAVE TRENDED TOWARD THE FASTER PROGRESSION SHOWN BY THE GFS  
AND ARE NOW VERY SIMILAR WITH TIMING OF THE TROUGH.  
HOWEVER...THERE REMAIN DIFFERENCES IN THE AMPLITUDE AND STRENGTH  
OF THE TROUGH. THERE IS ACTUALLY GOOD AGREEMENT BETWEEN THE 12Z  
GFS AND 12Z ECMWF ON MANY OF THE DETAILS...AND THEY ARE THE MODELS  
WITH THE CLOSEST MATCH TO THE 00Z ECMWF ENSEMBLE MEAN.  
THEREFORE...THE PREFERENCE IS ADJUSTED TOWARD A BLEND OF THE GFS  
AND ECMWF GIVEN IMPROVING AGREEMENT AND RELATIVELY GOOD AGREEMENT  
WITH THE ENSEMBLE MEANS.  
 
...ELONGATING SOUTHERN STREAM TROUGH AND DEVELOPING CLOSED LOW  
NEAR NORTHERN BAJA CALIFORNIA BY FRIDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 40 PERCENT 00Z ECMWF ENSEMBLE MEAN  
60 PERCENT SPLIT BETWEEN 12Z ECMWF/CMC/UKMET/NAM  
CONFIDENCE: 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.  
 
18Z UPDATE: CHANGE TO THE BLEND. THE 12Z GLOBAL MODELS CONTINUE TO  
SHOW IMPROVED AGREEMENT WITH THIS SYSTEM...AND NOW HAVE VERY  
SIMILAR PLACEMENT OF THE MID-UPPER LEVEL LOW. THIS HAS CONVERGED  
TO NEAR THE ECMWF ENSEMBLE MEAN...WHICH HAS BEEN MOST CONSISTENT  
OVER THE PAST SEVERAL MODEL CYCLES. THEREFORE...WILL CONTINUE TO  
WEIGHT THE BLEND TOWARD THE ECMWF ENSEMBLE MEAN...BUT WILL  
INCORPORATE SOME OF THE MORE REASONABLE MODEL SOLUTIONS. THE  
PRIMARY OUTLIER AT THIS POINT APPEARS TO BE THE 12Z GFS WITH A  
FASTER PROGRESSION OF THE PRIMARY LOW...AND A STRONGER SECONDARY  
LOW TO THE SOUTHWEST. OTHER MODELS NOW INDICATE A STRONGER LOW  
(CLOSER TO THE NAM SOLUTION)...AND GIVEN THIS TREND THE NAM IS  
INCORPORATED NOW...AS WELL AS THE CMC AND UKMET.  
 
...LOW AMPLITUDE SHORTWAVE REACHING THE PACIFIC NORTHWEST THURSDAY  
AND PROGRESSING NEAR US-CANADA BORDER THROUGH SATURDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z ECMWF / 12Z GFS / 12Z NAM  
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.  
 
18Z UPDATE: CHANGE TO THE BLEND TO REMOVE UKMET AND CMC. THE  
DETAIL DIFFERENCES WITH THIS SHORTWAVE REMAIN...AND THE IMPACTS ON  
SENSIBLE WEATHER CONTINUE TO LOOK RELATIVELY MINOR. HOWEVER...THE  
12Z CMC APPEARS TO BE MUCH BROADER AND STRONGER WITH THE SHORTWAVE  
THAN OTHER MODELS...AND THE 12Z UKMET HAS IT SPLIT INTO SEVERAL  
WAVES WHICH IS NOT SUPPORTED BY OTHER MODELS. ULTIMATELY THE  
DIFFERENCE ON THE UKMET EXTENDS TO THE LOW LEVELS WITH A LACK OF  
DEVELOPMENT OF A SURFACE LOW...WHICH IS SHOWN BY ALL OTHER MODELS.  
THEREFORE...THESE TWO MODELS WERE EXCLUDED FROM THE FINAL  
PREFERENCE.  
 
   
..GULF OF ALASKA TROUGH DIGGING INTO PACIFIC NORTHWEST BY SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF OPERATIONAL 12Z ECMWF / 12Z GFS / 12Z CMC  
ENSEMBLE 12Z GEFS MEAN / 00Z 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.  
 
18Z UPDATE: CHANGE TO THE BLEND TO REMOVE THE 12Z UKMET AND 12Z  
NAM. THE NAM CONTINUES TO SHOW THE FASTEST PROGRESSION OF THE  
APPROACHING WAVE...AND NOW APPEARS TO BE A BIT OF AN OUTLIER SO IT  
WAS EXCLUDED FROM THE FINAL PREFERENCE. THE 12Z UKMET NOW SHOWS  
MUCH MORE AMPLIFICATION OF THE TROUGH ALONG THE WEST COAST THAN  
OTHER AVAILABLE MODELS...SO IT WAS ALSO EXCLUDED. THE OPERATIONAL  
MODELS CONTINUE TO BE MORE AMPLIFIED THAN THE ENSEMBLE  
MEANS...SUGGESTING THAT THERE IS STILL A DECENT CHANCE THAT THE  
TROUGH COMES IN LESS AMPLIFIED THAN THE OPERATIONAL MODELS  
CURRENTLY HAVE. THEREFORE...THE FINAL PREFERENCE IS FOR THE  
ECMWF...GFS...AND CMC OPERATIONAL RUNS...TO BE BLENDED WITH THE  
12Z GEFS AND 00Z ECWMF ENSEMBLE MEANS.  
 
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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