984  
FXUS10 KWNH 181855  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
154 PM EST WED DEC 18 2019  
 
VALID DEC 18/1200 UTC THRU DEC 22/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCE AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..CLOSED MID-LEVEL LOW CROSSING NEW ENGLAND ON THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN VERY GOOD AGREEMENT WITH THIS SYSTEM, SO A  
GENERAL MODEL BLEND WILL BE PREFERRED.  
 
   
..SOUTHERN STREAM TROUGH CROSSING THE SOUTHWEST THROUGH THURS
 
   
..CROSSING THE SOUTHERN PLAINS/GULF COAST STATES FRI/SAT
 
   
..CYCLOGENESIS OVER THE GULF OF MEXICO
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...THROUGH 36 HOURS  
BLEND OF THE 12Z ECMWF/12Z GEFS MEAN AND 00Z ECENS  
MEAN...AFTER 36 HOURS  
CONFIDENCE: AVERAGE  
 
A SOUTHERN STREAM TROUGH ADVANCING INTO CENTRAL CA TODAY WILL  
ADVANCE EAST-SOUTHEAST AND CROSS THE SOUTHWEST THROUGH THURSDAY.  
THE ENERGY IS THEN EXPECTED TO CROSS THE SOUTHERN PLAINS AND GULF  
COAST STATES THROUGH SATURDAY WHILE DRIVING CYCLOGENESIS OVER THE  
CENTRAL GULF OF MEXICO. THE GUIDANCE IS IN RATHER GOOD AGREEMENT  
AT LEAST MASS FIELD WISE WITH THE SYSTEM THROUGH 36 HOURS,  
HOWEVER, THEREAFTER THE 12Z NAM BEGINS TO DROP THE ENERGY FARTHER  
SOUTH AND TO THE SOUTH OF THE GLOBAL MODEL CONSENSUS. BY THE END  
THE PERIOD, THE NAM SUGGESTS A CLOSED MID-LEVEL LOW OVER THE  
NORTHWEST GULF OF MEXICO WHICH IS WELL SOUTH OF THE GLOBAL MODEL  
ENSEMBLE SUITES. THE NAM REFLECTS MORE BACKING OF THE  
MID/UPPER-LEVEL FLOW DOWNSTREAM OVER THE GULF COAST WHICH DRIVES  
ITS GULF OF MEXICO SURFACE CYCLOGENESIS FARTHER NORTH THAN THE  
GLOBAL MODELS AND THUS A WETTER SOLUTION WITH STRONGER MOISTURE  
TRANSPORT AS A RESULT. OVERALL, THE 12Z GFS APPEARS TO BE A TAD  
TOO PROGRESSIVE AS THE ENERGY BEGINS TO CROSS THE GULF COAST  
STATES. THE 12Z ECMWF, 12Z GEFS MEAN AND 00Z ECENS MEAN ARE ALL  
SLOWER THAN THE GFS. THE 12Z CMC IS OVERALL RATHER CLOSE TO THE  
ECMWF SOLUTION, WITH THE 12Z UKMET FARTHER NORTH WITH ITS CLOSED  
LOW AND ALSO NOW THE SLOWEST SOLUTION. A GENERAL MODEL BLEND  
SHOULD SUFFICE THROUGH 36 HOURS, BUT THEREAFTER, A BLEND OF THE  
ECMWF/ECENS MEAN AND GEFS MEAN 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: SLIGHTLY ABOVE AVERAGE  
 
A NORTHERN STREAM SHORTWAVE EJECTING ACROSS THE PACIFIC NORTHWEST  
AND THE NORTHERN ROCKIES THROUGH THURSDAY WILL ADVANCE DOWNSTREAM  
ACROSS THE NORTHERN PLAINS AND MIDWEST THROUGH FRIDAY. THEREAFTER  
THE ENERGY WILL PROGRESSIVELY CROSS THE GREAT LAKES AND NORTHEAST.  
MODEL SPREAD IS MINIMAL WITH THIS SYSTEM, BUT AS THE ENERGY  
CROSSES THE GREAT LAKES AND NORTHEAST, THE 12Z NAM APPEARS TO BE A  
TAD TOO DEEP. WILL PREFER THE NON-NAM GLOBAL MODEL CONSENSUS.  
 
   
..DEEP UPPER TROUGH OFFSHORE THE WEST COAST
 
   
..ATMOSPHERIC RIVER IMPACTING THE PACIFIC NORTHWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS  
BLEND OF THE 12Z ECMWF/12Z GEFS MEAN AND 00Z ECENS  
MEAN...AFTER 60 HOURS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ONSHORE FLOW INTO THE PACIFIC NORTHWEST ON THURSDAY BEGINS TO  
ALTER AS A LARGE MID-UPPER LEVEL TROUGH UPSTREAM OVER THE EASTERN  
PACIFIC BEGINS TO AMPLIFY AND ENCROACH ON THE WEST COAST.  
PERSISTENT LOW-LEVEL SOUTHWEST FLOW WILL BE IMPACTING THE COASTAL  
RANGES OF WASHINGTON/OREGON WITH A TENDENCY FOR THE FLOW TO  
GRADUALLY BACK IN NATURE WITH TIME AS THE TROUGH AMPLIFIES, BUT  
ALSO AS MULTIPLE WAVES OF LOW PRESSURE RIDE NORTHEAST UP ALONG AN  
ATTENDANT FRONT. ONE FRONTAL WAVE WILL APPROACH VANCOUVER ISLAND  
BY THURSDAY EVENING, WITH A SECOND 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 DETAILS OF THESE WAVES, BUT THERE IS EXCELLENT  
AGREEMENT OUT OF THE GUIDANCE IN BRINGING SOME VERY STRONG ONSHORE  
FLOW INTO THE COASTAL RANGES AS A SOUTHWEST LOW-LEVEL JET OF AS  
MUCH AS 70 TO 80 KTS IS EXPECTED TO BE ARRIVING JUST AHEAD OF THE  
FRONT AND THESE SURFACE WAVES THURSDAY NIGHT AND 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 12Z UKMET SATURDAY APPEARS TO BE A  
LITTLE TOO SLOW WITH THE WAVE ACTIVITY AND IT ASSOCIATED FRONTAL  
TIMING, WHEREAS THE 12Z GFS MAY BE A TAD TOO FAST. A GENERAL MODEL  
BLEND SHOULD SUFFICE WITH THE DETAILS OF ALL OF THIS ENERGY GOING  
THROUGH ABOUT 60 HOURS, BUT THEREAFTER, A BLEND OF THE 12Z ECMWF,  
AND THE ENSEMBLE MEANS (00Z ECENS MEAN AND 12Z GEFS MEAN) WILL BE  
PREFERRED GIVEN BETTER OVERALL CLUSTERING.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.HTML  
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