020  
FXUS10 KWNH 090457  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 PM EST WED NOV 08 2017  
 
VALID NOV 09/0000 UTC THRU NOV 12/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH LATEST MODEL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...POSITIVELY TILTED TROUGH WITH MULTIPLE EMBEDDED SHORTWAVES  
CROSSING THE SOUTHEAST TODAY AND TONIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: NON-CMC BLEND  
70 PERCENT WEIGHT TO 12Z ECMWF AND 00Z GFS  
30 PERCENT WEIGHT TO 00Z NAM AND 00Z UKMET  
CONFIDENCE: ABOVE AVERAGE  
 
OTHER THAN THE 12Z CMC...WHICH IS SHOWING A HIGH BIAS WITH ITS  
HEIGHTS THROUGH MUCH OF THE TROPOSPHERE FROM THE SUBTROPICAL RIDGE  
OVER MEXICO INTO THE EASTERN CONUS...MODELS ARE IN GOOD AGREEMENT  
NOW ON THE TIMING AND AMPLITUDE OF THE PRIMARY SHORTWAVE. THEY  
ALSO ALL SHOW TWO WEAKER SHORTWAVES...ONE TO THE NORTHEAST OVER  
THE OHIO RIVER VALLEY THAT QUICKLY GETS SHEARED OUT...AND ANOTHER  
TO THE SOUTHWEST OVER TEXAS AND THE NW GULF OF MEXICO WHICH  
WEAKENS AS IT DIGS SOUTHEAST. THE AGREEMENT IS GOOD ENOUGH TO GO  
WITH A NON-CMC BLEND FOR THE PREFERENCE. THE UKMET IS SHOWING A  
MUCH STRONGER VORT MAX WITH THE PRIMARY SHORTWAVE (AND THE NAM TO  
A LESSER EXTENT). THESE DO SEEM SLIGHTLY OVERDONE IN RELATIVELY  
DEAMPLIFIED FLOW...SO THE WEIGHT IN THIS CASE WILL BE TOWARD THE  
GFS AND ECMWF.  
 
...DEEP CYCLONE OFFSHORE OF THE PACIFIC NORTHWEST OPENING INTO A  
TROUGH OVER THE NORTHWEST BY FRIDAY...   
..TROUGH MOVING EAST INTO THE NORTHERN PLAINS THIS WEEKEND
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
MODELS SHOW DECENT AGREEMENT THROUGH THE FIRST 24-36 HOURS AND  
THEN DIFFERENCES BEGIN TO EMERGE AND GROW AS THE LOW OPENS INTO A  
TROUGH. THE 12Z NAM IS STRONGER AND DEEPER WITH THE LOW INITIALLY  
AND MAINTAINS A MORE AMPLIFIED TROUGH AS IT PUSHES INTO THE  
NORTHWEST. THIS YIELDS LOWER HEIGHTS THROUGH MUCH OF THE REGION IN  
THE LOW-MID TROPOSPHERE AND A COLDER TEMPERATURE PROFILE. THIS  
BIAS IS NOT UNCOMMON IN THE NAM AND THE SOLUTION DOES NOT HAVE  
MUCH SUPPORT FROM THE GLOBAL MODELS.  
 
LOOKING TO THE GLOBAL MODELS...THE 00Z UKMET SEEMS TO SHOW A  
FASTER DEAMPLIFICATION OF THE WAVE...DESPITE A REASONABLY SIMILAR  
STRUCTURE TO THE ECMWF AND GFS. THE TEMPERATURE PROFILES END UP A  
LITTLE WARMER OVER PARTS OF THE NORTHWEST...PARTICULARLY NEAR THE  
CANADIAN BORDER...BEYOND 48 HOURS. THE 00Z GFS AND 12Z ECMWF ARE  
MUCH CLOSER TO THE ENSEMBLE MEANS AND SEEM TO BE A REASONABLE  
COMPROMISE BETWEEN THE SLOWER AND MORE AMPLIFIED NAM...AND THE  
FASTER AND LESS AMPLIFIED UKMET. THE 12Z CMC HAS A DIFFERENT  
STRUCTURE TO THE TROUGH OVERALL...WITH FLATTER WAVES AND AN  
UNRELATED SHORTWAVE THAT DIGS FROM NORTHERN CANADA TO NEAR NORTH  
DAKOTA BY SATURDAY NIGHT. GIVEN THE DIFFERENCES FROM THE CMC...AND  
THE EXTREMES THAT THE NAM AND UKMET REPRESENT...THE PREFERENCE IS  
FOR A COMPROMISE OF THE GFS AND ECMWF.  
 
   
..AMPLIFYING NORTHERN STREAM TROUGH/CLOSED LOW NEAR GREAT LAKES
 
   
..COLD FRONT CROSSING THE NORTHERN TIER STATES THROUGH FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW VERY GOOD AGREEMENT WITH THIS SYSTEM IN THE MASS  
FIELDS...WITH SIMILAR TIMING OF THE FRONT...PLACEMENT OF THE  
TROUGH...INTENSITY AND PLACEMENT OF THE SURFACE LOW...AND CENTER  
OF THE SURFACE HIGH. GIVEN THE GOOD AGREEMENT...A GENERAL MODEL  
BLEND IS PREFERRED.  
 
   
..UPPER TROUGH OFFSHORE OF THE PACIFIC NORTHWEST THIS WEEKEND
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AS THE TROUGH DROPS SOUTH OVER THE NORTHEAST PACIFIC...DIFFERENCES  
BEGIN TO EMERGE PRIMARILY RELATED TO TIMING AND PRECISE PLACEMENT  
OF THE MID-UPPER LEVEL LOW. THE 00Z NAM AND 12Z CMC ARE NOTABLY  
FURTHER SOUTH AND HAVE LOWER HEIGHTS THAN MOST (ALL IN SOME CASES)  
ENSEMBLE MEMBERS. FOR EXAMPLE...BY 12Z SUNDAY...THE CMC 564DM  
ISOHEIGHT AT 500MB IS WELL OUTSIDE THE SPREAD OF ALL ENSEMBLE  
MEMBERS. THE 00Z UKMET DID COME INTO SOMEWHAT BETTER AGREEMENT  
WITH THE GFS AND ECMWF...PARTICULARLY WITH THE CORE OF THE TROUGH.  
HOWEVER...IT HAS HIGHER HEIGHTS THROUGH THE BASE OF THE TROUGH AND  
THUS DEVELOPS A STRONGER JET AROUND THE BASE OF THE TROUGH. GIVEN  
THE LACK OF SUPPORT FROM ENSEMBLES FOR THE CMC...NAM...OR UKMET  
SOLUTIONS...A LEAN TOWARD THE GFS AND ECMWF IS PREFERRED.  
 
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