599  
FXUS10 KWNH 161856  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
155 PM EST SAT DEC 16 2017  
 
VALID DEC 16/1200 UTC THRU DEC 20/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH LATEST PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SHORTWAVE TROUGH EXITING THROUGH THE NORTHEAST TODAY/TONIGHT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE LATEST MODELS ARE IN GOOD AGREEMENT WITH THE DETAILS OF THE  
SHORTWAVE TROUGH CROSSING THROUGH THE NORTHEAST TODAY AND EXITING  
THROUGH THE CANADIAN MARITIMES TONIGHT. A GENERAL MODEL BLEND WILL  
BE PREFERRED.  
 
   
..UPPER LEVEL LOW CURRENTLY OVER NORTHERN MEXICO
 
   
..EJECTING NORTHEAST ACROSS THE SOUTHERN PLAINS BY TONIGHT
 
   
..DEAMPLIFYING ON SUNDAY AS IT SHEARS DOWNSTREAM
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z CMC GRADUALLY BECOMES A LITTLE SLOWER THAN THE MODEL  
CONSENSUS WITH THE UPPER LOW EJECTING NORTHEAST OUT OF NORTHERN  
MEXICO AND THEN WEAKENING INTO AN OPEN WAVE BEFORE SHEARING OUT  
OVER THE NEXT 24 TO 36 HOURS. THE REMAINING GUIDANCE IS GENERALLY  
WELL CLUSTERED WITH THEIR TIMING AND DEPTH...SO WILL FAVOR A  
NON-CMC BLEND AT THIS TIME.  
 
   
..SHORTWAVE DIGGING SHARPLY THROUGH SOUTHERN CA
 
   
..CLOSED LOW DEVELOPMENT OVER THE DESERT SOUTHWEST/NW MEXICO
 
   
..EJECTING OUT ACROSS THE SOUTHERN PLAINS ON TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE IN VERY GOOD AGREEMENT DIGGING A SHORTWAVE TROUGH  
DOWN THROUGH SOUTHERN CA TODAY AND THEN ACROSS THE NORTHERN BAJA  
PENINSULA TONIGHT WHERE THE ENERGY SHOULD DEEPEN AND CLOSE OFF. A  
CLOSED LOW CENTER IS THEN EXPECTED TO GRADUALLY PIVOT EAST ACROSS  
FAR NORTHWEST MEXICO THROUGH MONDAY BEFORE THEN ADVANCING  
DOWNSTREAM OUT ACROSS THE SOUTHERN PLAINS THROUGH TUESDAY. THE  
HEIGHT FALLS WILL LIKELY INDUCE AT LEAST A WEAK AREA OF LOW  
PRESSURE ACROSS THE SOUTHEAST TX COASTAL PLAIN BY LATE TUESDAY  
WHICH SHOULD BE FOCUSED ALONG A FRONTAL ZONE. THE GUIDANCE IS IN  
RATHER GOOD AGREEMENT UNTIL TUESDAY WHEN THE 12Z CMC BECOMES A  
LITTLE SLOWER THAN THE REMAINING GUIDANCE. THE 12Z NAM ALSO  
OVERALL APPEARS TO PERHAPS BE A TAD TOO SHARP AND A LITTLE TOO  
AGGRESSIVE IN SUGGESTING SOME NEGATIVE TILT TO ITS TROUGH AXIS AT  
THE END OF THE PERIOD. THE 12Z GFS IS NOW THE FASTEST  
SOLUTION...WITH THE 12Z UKMET AND 12Z ECMWF NOW CLUSTERING  
TOGETHER IN BETWEEN THE FASTER GFS AND SLOWER CMC. THE FASTER GFS  
IS NOT WELL SUPPORTED BY THE 12Z GEFS MEAN WHICH ACTUALLY FAVORS  
THE MODESTLY SLOWER UKMET/ECMWF CLUSTER. THEREFORE...BASED ON THE  
LATEST TRENDS AND MORE AGREEABLE MODEL CLUSTERING...A BLEND OF THE  
UKMET AND ECMWF WILL BE PREFERRED.  
 
   
..SHORTWAVE TRAVERSING THE NORTHERN ROCKIES/PLAINS TODAY/SUNDAY
 
   
..ENERGY DAMPENING OUT OVER THE GREAT LAKES/NORTHEAST BY MONDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
THE NORTHERN PORTION OF THE SHORTWAVE TROUGH THAT CAME INTO THE  
PACIFIC NORTHWEST LAST NIGHT WILL MOVE ACROSS THE NORTHERN ROCKIES  
TODAY AND ACROSS THE NORTHERN PLAINS ON SUNDAY. ON MONDAY THE  
ENERGY WILL BEGIN TO DAMPEN OUT AS IT CROSSES THE GREAT LAKES  
REGION AND THE NORTHEAST. A WEAK AREA OF LOW PRESSURE ALONG A  
FRONTAL ZONE OVER THE CENTRAL PLAINS/MIDWEST WILL BREAK AWAY AND  
CROSS PARTS OF THE GREAT LAKES AND NORTHEAST AS THIS ENERGY  
CROSSING THE NORTHERN TIER OF THE COUNTRY. DIFFERENCES WITH THIS  
SYSTEM ARE SMALL SCALE AND MAINLY NOTED WITH THE 12Z UKMET AND 12Z  
ECMWF FAVORING A SLIGHTLY STRONGER REMNANT SHORTWAVE FEATURE THAT  
CROSSES THE NORTHEAST...VERSUS THE WEAKER 12Z NAM/12Z GFS AND 12Z  
UKMET. THE FLOW DOES BECOME QUITE ZONAL ACROSS THE REGION BY  
MONDAY WHICH WOULD TEND TO SUPPORT A WEAKER/SHEARED SOLUTION...BUT  
FOR NOW WILL RECOMMEND A GENERAL MODEL BLEND TO RESOLVE THE  
SMALLER SCALE DIFFERENCES.  
 
   
..AMPLIFYING NORTHERN STREAM TROUGH OVER SOUTHERN CANADA MONDAY
 
   
..ENERGY DIGGING ACROSS THE MIDWEST/GREAT LAKES BY TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS TAKE SHORTWAVE ENERGY THAT ARRIVES ACROSS NORTHERN  
BRITISH COLUMBIA FROM THE GULF OF AK AND DIGS IT AGGRESSIVELY  
SOUTHEAST OVER THE NEXT FEW DAYS WHICH ALLOWS A RATHER STRONG  
NORTHERN STREAM TROUGH TO CROSS SOUTHERN CANADA AND THE NORTHERN  
U.S. WITH IMPACTS ACROSS THE NORTHERN PLAINS/MIDWEST AND GREAT  
LAKES THROUGH MONDAY AND TUESDAY. A STRONG COLD FRONT WILL  
ACCOMPANY THESE HEIGHT FALLS. THE MODELS ARE IN RATHER GOOD  
AGREEMENT WITH THE LARGE SCALE DETAILS OF THE TROUGH AND THE COLD  
FRONT. THE UKMET WHICH HAD BEEN TRACKING ITS SURFACE LOW SOUTH OF  
THE MODEL CONSENSUS HAS TRENDED A BIT FARTHER NORTH WITH ITS 12Z  
CYCLE AND IS NOW IN LINE WITH THE MULTI-MODEL CONSENSUS. WILL  
PREFER A GENERAL MODEL BLEND AS A RESULT.  
 
   
..DEEP UPPER TROUGH/CLOSED LOW CROSSING THE GULF OF AK MONDAY
 
   
..ENERGY DIGGING SHARPLY INTO THE PACIFIC NORTHWEST ON TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS TAKE A NORTHERN STREAM SHORTWAVE TROUGH OVER THE GULF  
OF AK AND AMPLIFY IT SOUTHEAST TOWARD THE PACIFIC NORTHWEST ON  
TUESDAY WHICH ALLOWS FOR SOME STRONG HEIGHT FALLS TO ARRIVE IN  
CONJUNCTION WITH A DEEPENING AREA OF LOW PRESSURE. THIS LOW  
PRESSURE WAVE MOVES ACROSS NORTHWEST WA BY LATE TUESDAY. THE  
MODELS ARE WELL CLUSTERED WITH TIMING AND DEPTH UNTIL TUESDAY WHEN  
SOME DIFFERENCES ARE NOTED. THE 12Z ECMWF TRENDED A BIT MORE  
PROGRESSIVE WITH ITS LATEST RUN AND IS CLOSE TO THE MODEL  
CONSENSUS AS THE ENERGY ARRIVES ACROSS THE NORTHWEST. THE 12Z  
UKMET THOUGH HAS SET ITSELF OUT AS BEING THE STRONGEST SOLUTION AT  
THE SURFACE AND ALOFT BY TUESDAY...AND IS LIKELY TOO STRONG BASED  
ON THE LATEST ENSEMBLE GUIDANCE. THE 12Z NAM FOR ITS PART LOOKS TO  
BE A TAD TOO WEAK WITH ITS SURFACE LOW. THE 12Z CMC ALSO NOW  
APPEARS TO BE TRACKING ITS SURFACE LOW A TAD TOO FAR SOUTH AS IT  
APPROACHES WA STATE. THE BETTER MODEL CLUSTERING AND ENSEMBLE  
SUPPORT WOULD SUGGEST A BLEND OF THE GFS AND ECMWF AND THAT WILL  
BE THE PREFERENCE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page