801  
FXUS10 KWNH 121628  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1127 AM EST TUE DEC 12 2017  
 
VALID DEC 12/1200 UTC THRU DEC 16/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..DEEPENING/NEGATIVELY TILTED CYCLONE IMPACTING THE NORTHEAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS OVER THE NEXT 36 HOURS SHOW GOOD MASS FIELD AGREEMENT  
WITH THE DETAILS OF THE STRENGTHENING AND NEGATIVELY TILTING  
TROUGH OVER THE NORTHEAST. LOW PRESSURE INITIALLY OVER WESTERN NY  
WILL RECONSOLIDATE OVER SOUTHERN NEW ENGLAND LATER THIS AFTERNOON  
AND THEN LIFT NORTH UP ACROSS CENTRAL AND DOWNEAST MAINE BY EARLY  
WEDNESDAY. THE SYSTEM WILL EXIT UP ACROSS QUEBEC ON THURSDAY. WILL  
PREFER A GENERAL MODEL BLEND AT THIS TIME.  
 
   
..STRONG SHORTWAVE ENTERING BRITISH COLUMBIA TODAY
 
   
..ENERGY AND ASSOCIATED CLIPPER LOW DIGGING SOUTHEAST
 
   
..CROSSING THE UPPER MIDWEST/OH VALLEY/MID-ATLANTIC WED/THURS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC CONSENSUS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE GUIDANCE SHOWS A STRONG PACIFIC SHORTWAVE CURRENTLY CROSSING  
BRITISH COLUMBIA THAT WILL DIGGING SOUTHEASTWARD OVER THE NEXT 48  
HOURS AND AMPLIFY ACROSS THE UPPER MIDWEST/OH VALLEY AND  
MID-ATLANTIC REGION. AN ASSOCIATED CLIPPER-TYPE SURFACE LOW WILL  
CROSS THE REGION AND THEN QUICKLY EJECT OFFSHORE SOUTHERN NEW  
ENGLAND ON THURSDAY. THE 00Z CMC WAS A LITTLE SLOWER THAN THE  
MODEL CONSENSUS...
AND WITH THE REMAINING GUIDANCE RATHER WELL  
CLUSTERED...A NON-CMC CONSENSUS WILL BE PREFERRED.  
 
   
..SHORTWAVE DIGGING SOUTH ACROSS THE PLAINS THURS
 
   
..ENERGY CROSSING THE LOWER MS/TN VALLEYS ON FRI
 
   
..POSSIBLE SURFACE LOW DEVELOPMENT OFF THE MID-ATLANTIC ON FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
A SHORTWAVE CRESTING THE TOP OF THE WESTERN NORTH AMERICA RIDGE  
AXIS WILL DROP SOUTH DOWN FROM THE NORTHWEST TERRITORIES IN CANADA  
AND THEN DOWN ACROSS THE PLAINS THURSDAY BEFORE SWEEPING ACROSS  
THE LOWER MS AND TN VALLEY REGION ON FRIDAY. THIS ENERGY IS  
EXPECTED TO HELP RELOAD A LARGER SCALE LONGWAVE TROUGH ACROSS THE  
EASTERN U.S. BY THE END OF THE WEEK AND WILL ENCOURAGE A SURFACE  
LOW DEVELOPING OFFSHORE THE MID-ATLANTIC AS WELL. THE 12Z NAM IS  
OVERALL THE SLOWEST AND STRONGEST MODEL WITH THIS FEATURE...WITH  
THE REMAINING GUIDANCE RATHER WELL CLUSTERED TOWARD A SOMEWHAT  
MORE PROGRESSIVE AND FLATTER SOLUTION. ALL OF THE MODELS SUPPORT  
AT LEAST A WEAK SURFACE WAVE OFFSHORE THE MID-ATLANTIC BY THE END  
OF THE PERIOD...BUT WITH THE SHORTWAVE ENERGY GENERALLY SHEARING  
OUT...THE SURFACE WAVE SHOULD TEND TO BE ELONGATED AND MAY  
ACTUALLY TAKE THE FORM OF MULTIPLE WAVES. WILL PREFER A NON-NAM  
CONSENSUS AT THIS TIME.  
 
   
..NEW UPPER LOW DROPPING SOUTH TOWARD THE GREAT LAKES BY FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/00Z CMC AND 00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS TAKE ARCTIC SHORTWAVE ENERGY CURRENTLY UP OVER NUNAVUT  
IN NORTHERN CANADA DOWN TO THE SOUTH OVER THE NEXT COUPLE OF DAYS  
WHICH RESULTS IN A NEW UPPER LOW DROPPING SOUTH OVER HUDSON BAY  
AND THEN ACROSS ONTARIO BY THE END OF THE WEEK. THIS WILL RESULT  
IN HEIGHT FALLS ENCROACHING ON THE GREAT LAKES REGION AND A WAVE  
OF LOW PRESSURE IMPACTING THIS REGION. THE 12Z NAM DIGS THE ENERGY  
FARTHEST SOUTH AND CROSSING THE UPPER GREAT LAKES...WITH THE 00Z  
UKMET GENERALLY THE FARTHEST EAST AND MORE OVER TOWARD EASTERN  
ONTARIO. THE 12Z GFS/00Z CMC AND 00Z ECMWF ARE ALL CLUSTERED OVER  
CENTRAL ONTARIO BY THE END OF THE PERIOD. THE 06Z GEFS MEAN AND  
00Z ECENS MEAN SUPPORT THE GFS/CMC/ECMWF CLUSTER AND SO A BLEND OF  
THESE SOLUTIONS WILL BE PREFERRED.  
 
   
..SHORTWAVE TROUGH ARRIVING ACROSS THE PACIFIC NORTHWEST ON FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z UKMET  
CONFIDENCE: AVERAGE  
 
THE MODELS BREAK DOWN THE WESTERN NORTH AMERICA RIDGE BY THE END  
OF THE WEEK AND THIS ALLOWS A SHORTWAVE TROUGH AND ASSOCIATED COLD  
FRONT TO ARRIVE ACROSS THE PACIFIC NORTHWEST BY THE END OF THE  
WEEK. THE 00Z CMC IS A SLOW OUTLIER AND EVEN THE 00Z ECMWF ALSO  
APPEARS TO BE A LITTLE SLOWER THAN THE MODEL CONSENSUS. THE 12Z  
NAM/12Z GFS AND 00Z UKMET ARE ALL MORE PROGRESSIVE WHICH IS  
SUPPORTED BY THE 00Z ECENS MEAN AND 06Z GEFS MEAN. HOWEVER...THE  
NAM MAY BE SLOWING DOWN THE NORTHERN PORTION OF THE TROUGH AXIS A  
BIT TOO MUCH BY THE END OF THE PERIOD OVER WESTERN CANADA. WILL  
LEAN TOWARD THE MORE PROGRESSIVE CONSENSUS WITH A BLEND OF THE GFS  
AND UKMET.  
 
   
..UPPER LEVEL LOW OVER THE BAJA PENINSULA/GULF OF CALIFORNIA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/00Z UKMET AND 00Z ECMWF  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE 12Z NAM AND 00Z CMC GRADUALLY CLUSTER THE UPPER LOW OVER THE  
BAJA PENINSULA DOWN TO THE SOUTH THROUGH THE PERIOD...AND WELL  
WEST OF THE 12Z GFS/00Z UKMET AND 00Z ECMWF BY FRIDAY. THE  
GFS/UKMET AND ECMWF SOLUTIONS TAKE THE UPPER LOW MORE SOUTHEAST  
AND DOWN OVER NORTHWEST MAINLAND MEXICO. THE 00Z ECENS MEAN  
SUPPORTS THE FARTHER EAST CONSENSUS...HOWEVER THE 06Z GEFS MEAN  
FAVORS THE FARTHER WEST NAM/CMC CAMP. WILL FOR NOW LEAN TOWARD THE  
FARTHER EAST CONSENSUS VIA A BLEND OF THE GFS/UKMET AND ECMWF.  
CONFIDENCE IS SOMEWHAT LIMITED.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 
 

 
 

 
 
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