069  
FXUS10 KWNH 121853  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
153 PM EST SUN NOV 12 2017  
 
VALID NOV 12/1200 UTC THRU NOV 16/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH LATEST MODEL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..LEAD SHORTWAVE CROSSING SOUTHERN QUEBEC/NORTHERN MAINE
 
   
..REACHING THE CANADIAN MARTIMES BY MONDAY MORNING
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THERE ARE NO APPRECIABLE DIFFERENCES IN THE MODEL MASS FIELDS FOR  
THIS SYSTEM AND THUS A GENERAL MODEL BLEND WILL BE PREFERRED.  
 
   
..BROAD SECONDARY TROUGH OVER THE MIDWEST PUSHING EAST
 
 
...AMPLIFICATION OVER THE EASTERN CONUS THROUGH MONDAY WITH  
SURFACE WAVE DEVELOPMENT OFF THE EAST COAST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET...12Z CMC AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM THROUGH TONIGHT  
AS IT CROSSES THE MIDWEST AND OH VALLEY. AS THE ENERGY REACHES THE  
MID-ATLANTIC AND NORTHEAST ON MONDAY IT WILL BEGIN TO AMPLIFY  
SOMEWHAT AND SHOULD FOSTER A WAVE OF LOW PRESSURE EAST OF NEW  
ENGLAND LATER MONDAY NIGHT BEFORE THEN LIFTING NORTHEAST AND OUT  
TO SEA ON TUESDAY. THE 12Z NAM OVERALL IS THE DEEPEST SOLUTION  
WITH RESPECT TO THE LEVEL OF TROUGH AMPLIFICATION...HOWEVER THE  
12Z GFS WHICH HAD BEEN WEAKER HAS TRENDED A BIT STRONGER AND  
ACTUALLY BECOMES THE MOST AMPLIFIED SOLUTION AS THE SYSTEM EXITS  
OFFSHORE. THE 12Z UKMET/12Z CMC AND 12Z ECMWF ARE ALL WEAKER BY  
COMPARISON. THE LATEST THINKING IS THAT THE NAM AND GFS ARE BOTH  
NOW A TAD TOO DEEP AS THE WEAKER CONSENSUS LED PARTICULARLY BY THE  
ECMWF HAS BEEN QUITE CONSISTENT. ADDITIONALLY...THERE IS RATHER  
LIMITED ENSEMBLE SUPPORT FOR THE STRONGER GFS OFFSHORE. SO WILL  
PREFER THE WEAKER CONSENSUS.  
 
   
..UPPER TROUGH/CLOSED LOW OFFSHORE OF THE PACIFIC NORTHWEST
 
 
...UPPER LEVEL LOW DEVOLVING TO A SHORTWAVE AND EJECTING EAST TO  
THE NORTHERN PLAINS/MIDWEST BY WEDNESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE GUIDANCE ALLOWS A DEEP UPPER TROUGH AND ASSOCIATED CLOSED LOW  
TO DROP SOUTH THROUGH TODAY OFFSHORE THE PACIFIC NORTHWEST BEFORE  
THEN PIVOTING EAST AND INLAND ACROSS THE NORTHWEST THROUGH MONDAY.  
THIS WILL DRIVE LOW PRESSURE ACROSS VANCOUVER ISLAND AND A COLD  
FRONT INLAND ACROSS THE COASTAL RANGES OF WA/OR AND INTERIOR  
SECTIONS OF THE NORTHWEST. BY TUESDAY...THIS ENERGY WILL BE  
RAPIDLY MOVING DOWNSTREAM ACROSS THE NORTHERN PLAINS AS A  
PROGRESSIVE SHORTWAVE TROUGH. ON WEDNESDAY THE ENERGY WILL BE  
TENDING TO AMPLIFY A BIT ACROSS THE UPPER MIDWEST AND GREAT LAKES  
REGION.  
 
THE 12Z NAM APPEARS TO BE A LITTLE SLOW AND PERHAPS A TAD TOO FAR  
SOUTH WITH THE ARRIVAL SURFACE LOW PRESSURE NEAR THE OLYMPIC  
PENINSULA AND THE SOUTHERN TIP OF VANCOUVER ISLAND. THE 12Z CMC  
FOR ITS PARTS ALSO IS PROBABLY TOO SLOW BUT APPEARS TOO FAR NORTH.  
THE 12Z GFS AND 12Z UKMET AND 12Z ECMWF ARE CLUSTERED TOGETHER IN  
BETWEEN THE NAM AND CMC BUT ARE A TAD MORE PROGRESSIVE. DOWNWIND  
AS THE ENERGY OPENS UP INTO A PROGRESSIVE TROUGH ALOFT CROSSING  
THE NORTHERN PLAINS AND MIDWEST...THE 12Z NAM BECOMES LIKELY TOO  
WEAK AND TOO FAR NORTH WITH ITS SURFACE LOW EVOLUTION...AND THE  
12Z UKMET ALSO APPEARS A BIT TOO WEAK PROBABLY A BIT TOO SLOW.  
BETTER MODEL CLUSTERING AND ENSEMBLE SUPPORT RESIDES WITH THE GFS  
AND ECMWF...AND THUS A BLEND OF THESE SOLUTIONS WILL BE PREFERRED.  
 
   
..DEEP CYCLONE REFORMING OFFSHORE BRITISH COLUMBIA BY TUESDAY
 
   
..ENERGY IMPACTING THE PACIFIC NORTHWEST BY WEDNESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: AVERAGE  
 
A NEW DEEP CLOSED LOW WILL BE FORMING AND DROPPING SOUTH OFFSHORE  
BRITISH COLUMBIA BY TUESDAY...AND SETTING THE STAGE FOR DEEP LAYER  
CYCLONIC AND ONSHORE FLOW TO IMPACT THE COASTAL RANGES OF THE  
PACIFIC NORTHWEST. THE 12Z NAM IS THE SLOWEST IN BRINGING THE  
HEIGHT FALLS/ENERGY TOWARD THE PACIFIC NORTHWEST BY WEDNESDAY AND  
IS ALSO PROBABLY BIT TOO WEAK WITH ITS SURFACE LOW. THE REMAINING  
MODELS ARE RATHER WELL CLUSTERED TOGETHER WITH TIMING AND  
DEPTH...AND SO WILL PREFER A NON-NAM BLEND AS A RESULT.  
 
   
..SHORTWAVE AMPLIFYING OVER THE NORTHEAST BY LATE TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM...12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE COLLECTIVELY BEGINNING TO TREND TOWARD THE STRONGER  
GFS SOLUTION WITH ITS MORE AMPLIFIED TROUGH DIGGING SOUTHEAST  
ACROSS SOUTHERN QUEBEC AND THE NORTHEAST BY LATE TUESDAY. THE CMC  
AND TO A LESSER EXTENT THE UKMET ARE THE WEAKEST SOLUTIONS...BUT  
THEY HAVE BOTH TRENDED STRONGER WITH THEIR 12Z RUNS. THE ECMWF IS  
CLOSE TO THAT OF THE NAM SOLUTION AND ONLY A TAD WEAKER THAN THE  
GFS. THE LATEST GEFS MEAN FROM 12Z SUPPORTS THE STRONGER  
CONSENSUS. WILL THEREFORE TREND STRONGER WITH THE PREFERENCE AND  
FAVOR A NAM/GFS AND ECMWF BLEND.  
 
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ORRISON  
 

 
 
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