565  
FXUS10 KWNH 191646  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1145 AM EST THU DEC 19 2019  
 
VALID DEC 19/1200 UTC THRU DEC 23/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCE AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SOUTHERN STREAM TROUGH CROSSING THE SOUTHWEST TODAY
 
   
..CROSSING THE SOUTHERN PLAINS/GULF COAST STATES FRI/SAT
 
   
..CYCLOGENESIS OVER THE GULF OF MEXICO
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM/00Z UKMET AND 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
A SOUTHERN STREAM TROUGH ADVANCING ACROSS THE SOUTHWEST TODAY WILL  
CROSS THE SOUTHERN PLAINS AND GULF COAST STATES THROUGH SATURDAY  
WHILE DRIVING CYCLOGENESIS OVER THE CENTRAL GULF OF MEXICO. THIS  
SYSTEM WILL MOVE INTO THE SOUTHEAST ON SUNDAY. GENERALLY SPEAKING,  
AND FITTING IN WITH ITS BIAS, THE 12Z GFS AND LATEST GEFS MEMBER  
SUITE AGAIN APPEAR TO BE TOO PROGRESSIVE WITH THE EVOLUTION OF  
THIS SYSTEM AS IT IMPACTS THE GULF COAST AND SOUTHEAST GOING  
THROUGH THE WEEKEND. THE 00Z CMC IS ALSO AN OUTLIER WITH ITS  
CLOSED LOW PLACEMENT MUCH FARTHER NORTH AND EAST OF THE MODEL  
CONSENSUS BY THE END OF THE PERIOD. THE BETTER ENSEMBLE (00Z ECENS  
SUITE) AND DETERMINISTIC CLUSTERING SUGGESTS A SLOWER SOLUTION  
THAT IS CLOSE TO A BLEND OF THE 12Z NAM, 00Z UKMET AND 00Z ECMWF  
AT THIS POINT, AND SO A BLEND OF THESE SLOWER SOLUTIONS WILL BE  
PREFERRED.  
 
   
..NORTHERN STREAM TROUGH CROSSING THE NORTHERN PLAINS/MIDWEST
 
   
..ENERGY ARRIVING ACROSS THE GREAT LAKES/NORTHEAST BY SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A NORTHERN STREAM SHORTWAVE WILL ADVANCE DOWNSTREAM ACROSS THE  
NORTHERN PLAINS AND MIDWEST THROUGH FRIDAY. THEREAFTER THE ENERGY  
WILL PROGRESSIVELY CROSS THE GREAT LAKES AND NORTHEAST. THE 12Z  
NAM APPEARS TO BE A BIT TOO SLOW AND TOO DEEP AS THE SYSTEM  
ARRIVES ACROSS THE NORTHEAST, AND SO A NON-NAM BLEND WILL BE  
PREFERRED WITH THIS SYSTEM.  
 
   
..DEEP UPPER TROUGH OFFSHORE THE WEST COAST
 
   
..ATMOSPHERIC RIVER IMPACTING THE PACIFIC NORTHWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z UKMET/ECMWF AND 00Z ECENS/06Z GEFS MEAN BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
PERSISTENT LOW-LEVEL SOUTHWEST FLOW WILL BE IMPACTING THE COASTAL  
RANGES OF WASHINGTON/OREGON AS MULTIPLE WAVES OF LOW PRESSURE RIDE  
NORTHEAST UP ALONG AN OFFSHORE FRONTAL ZONE ASSOCIATED WITH AN  
AMPLIFYING UPPER TROUGH. ONE FRONTAL WAVE WILL APPROACH VANCOUVER  
ISLAND BY LATE THIS AFTERNOON, WITH A MORE SUBTLE WAVE APPROACHING  
BY FRIDAY MORNING A BIT FARTHER SOUTH DOWN TOWARD COASTAL AREAS OF  
NORTHWEST OREGON AND SOUTHWEST WASHINGTON. THERE IS VERY MODEST  
SPREAD WITH THE TIMING/DEPTH DETAILS OF THESE WAVES, BUT  
REGARDLESS, THE MODELS ALL AGREE ON BRINGING VERY STRONG ONSHORE  
FLOW/ATMOSPHERIC RIVER CONDITIONS INTO THE COASTAL RANGES AS A  
SOUTHWEST LOW-LEVEL JET OF AS MUCH AS 70+ KTS IS EXPECTED TO BE  
ARRIVING JUST AHEAD OF THE FRONT AND THESE SURFACE WAVES GOING  
THROUGH FRIDAY MORNING. ADDITIONAL WAVE ACTIVITY IS FORECAST TO  
LIFT UP ALONG THE FRONT FRIDAY NIGHT AND SATURDAY AS THE FRONT  
SETTLES SLOWLY SOUTHEASTWARD AND BEGINS TO EDGE INLAND FARTHER  
SOUTH DOWN ACROSS NORTHWEST CALIFORNIA. THE MODELS ALL BRING THE  
UPSTREAM TROUGH BODILY INLAND ACROSS THE WEST COAST BY SUNDAY. THE  
12Z GFS AND PERHAPS TO SOME EXTENT THE 12Z NAM APPEAR TO BE A TAD  
TOO PROGRESSIVE WITH THE ENERGY ADVANCING INLAND (ESPECIALLY  
RELATIVE TO CALIFORNIA). MEANWHILE, THE 00Z CMC IS LIKELY A LITTLE  
TOO SLOW. THE BETTER MODEL CLUSTERING WOULD TEND TO FAVOR THE 00Z  
UKMET/ECMWF SOLUTIONS WHICH HAVE GOOD SUPPORT FROM THE 00Z ECENS  
MEAN AND 06Z GEFS MEAN, AND SO A BLEND OF THESE SOLUTIONS WILL BE  
PREFERRED.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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