022  
FXUS10 KWNH 130502  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1202 AM EST MON NOV 13 2017  
 
VALID NOV 13/0000 UTC THRU NOV 16/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION WITH LATEST MODEL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...UPPER LEVEL LOW DEVOLVING TO A SHORTWAVE AND EJECTING THROUGH  
THE PACIFIC NORTHWEST INTO SOUTHERN CANADA BY TUESDAY...  
...EASTWARD TROUGH PROGRESSION OVER THE GREAT LAKES  
WEDNESDAY...AND THE NORTHEAST BY THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z GFS / 00Z NAM / 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS ARE GENERALLY IN GOOD AGREEMENT THROUGH THE FIRST 36 HOURS  
OF THE FORECAST AS THE UPPER LEVEL LOW OPENS UP INTO A TROUGH AND  
PUSHES INTO THE PACIFIC NORTHWEST...AND THE ACCOMPANYING OCCLUDING  
SURFACE LOW APPROACHES VANCOUVER ISLAND BEFORE DISSIPATING.  
GREATER DIFFERENCES BEGIN TO EMERGE AS THE TROUGH REACHES CENTRAL  
CANADA AND THE NORTHERN PLAINS AND EVENTUALLY AS GRADUAL  
AMPLIFICATION TAKES PLACE INTO THE GREAT LAKES AND NORTHEAST.  
 
ON THE 12Z MODEL CYCLE...THE GFS AND UKMET WERE CLEARLY SLOWER  
WITH THE TROUGH AS IT MOVED INTO THE GREAT LAKES...AND WERE NEAR  
THE EXTREME END OF THE GEFS...CMC...AND ECMWF ENSEMBLE MEMBERS.  
THE GEFS MEMBERS DID HAVE A SLOWER BIAS OVERALL AS WELL...WITH THE  
MAJORITY OF CMC AND ECMWF ENSEMBLE MEMBERS FASTER. THE 00Z GFS HAS  
TRENDED FASTER THAN PREVIOUS RUNS OF THE MODEL...WHICH LENDS MORE  
CONFIDENCE TO THE SCENARIO DEPICTED BY THE ECMWF AND CMC ENSEMBLE  
MEANS.  
 
THE 12Z UKMET IS STILL SLOWER...SO THAT IS EXCLUDED FROM THE  
PREFERENCE AT THIS TIME. ADDITIONALLY...THE 12Z OPERATIONAL CMC IS  
WEAKER WITH THE TROUGH SHOWING HIGHER HEIGHTS THAN THE OTHER  
MODELS...AND HAS WEAKER MID-UPPER LEVEL VORTICITY AS WELL.  
THEREFORE...THE PREFERENCE IS FOR A NON-CMC AND NON-UKMET BLEND AT  
THIS TIME...AND MODEL AGREEMENT IS SUCH THAT A GENERAL BLEND COULD  
PROBABLY BE USED PRIOR TO 36 HOURS (12Z TUESDAY).  
 
   
..DEEP CYCLONE REFORMING OFFSHORE BRITISH COLUMBIA BY TUESDAY
 
 
...OPENING INTO A TROUGH AND PUSHING INTO THE PACIFIC NORTHWEST  
LATE WEDNESDAY AND INTO THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z ECMWF ENSEMBLE NORMALIZED STANDARD DEVIATION FOR MUCH OF  
THE CORE OF THE TROUGH AND ASSOCIATED SURFACE CYCLONE ON WEDNESDAY  
AND THURSDAY IS LESS THAN 1...INDICATING LESS-THAN-USUAL MODEL  
SPREAD. ALTHOUGH THERE ARE DIFFERENCES ARISING FROM SMALL EMBEDDED  
WAVES ROTATING AROUND THE PRIMARY CYCLONE...AND THESE DO HAVE SOME  
IMPACT ON THE MASS FIELDS...THE MODELS ARE OVERALL IN VERY GOOD  
AGREEMENT. THERE IS NOT A SUBSTANTIAL ENOUGH INDIVIDUAL MODEL BIAS  
THAT ANY CAN BE EXCLUDED FROM THE PREFERENCE FOR THIS SYSTEM.  
THEREFORE...A GENERAL MODEL BLEND IS RECOMMENDED AS THIS WILL  
ACCOUNT FOR THE SMALL DETAIL DIFFERENCES THAT ARE REASONABLE  
POSSIBILITIES.  
 
...TROUGH CROSSING THE EASTERN CONUS THROUGH TONIGHT WITH SURFACE  
LOW DEVELOPMENT WELL OFF THE EAST COAST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 12Z CMC CONTINUES TO SHOW CONSISTENTLY HIGHER HEIGHTS THROUGH  
MUCH OF THE TROUGH OVER THE EASTERN CONUS...AND IS THE ONLY MODEL  
THAT SHOWS THIS. THIS HAS BEEN CHARACTERISTIC OF THE PAST SEVERAL  
MODEL CYCLES. OTHERWISE...
MODELS ARE IN VERY GOOD AGREEMENT WITH  
THIS SYSTEM. THEREFORE A NON-CMC BLEND IS THE PREFERENCE.  
 
   
..SHORTWAVE AMPLIFYING OVER THE NORTHEAST BY LATE TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z GFS / 00Z NAM / 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 12Z CMC AND 12Z UKMET SHOW A LESS AMPLIFIED AND WEAKER WAVE  
OVERALL IN THE NORTHEAST...WHILE THE 00Z NAM...00Z GFS...AND 12Z  
ECMWF ARE MORE AMPLIFIED AND EVEN GENERATE A CLOSED LOW ALOFT FOR  
A BRIEF TIME. THE PREVIOUS PREFERENCE WAS FOR THE STRONGER  
SOLUTION...AND THIS DOES HAVE MORE SUPPORT FROM THE GEFS AND ECMWF  
ENSEMBLE CLUSTERS. AROUND 75 PERCENT OF THE ENSEMBLE MEMBERS FAVOR  
THE STRONGER SOLUTION. THEREFORE THE PREFERENCE IS TO CONTINUE  
WITH THE BLEND OF THE NAM...GFS...AND ECMWF.  
 
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WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
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