884  
FXUS10 KWNH 200446  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1245 AM EDT FRI OCT 20 2017  
 
VALID OCT 20/0000 UTC THRU OCT 23/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION ALONG WITH LATEST MODEL PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SHORTWAVE CURRENTLY CLIPPING NORTHERN NEW ENGLAND
 
   
..ASSOCIATED COLD FRONT CROSSING THE NORTHEAST BY WEEKS END
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM...SO A GENERAL  
MODEL COMPROMISE WILL BE PREFERRED.  
 
   
..SOUTHERN STREAM UPPER TROUGH REACHING THE SOUTHERN PLAINS FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM EJECTING OUT  
ACROSS THE SOUTHERN HIGH PLAINS OUT AHEAD OF THE STRONGER UPSTREAM  
LONGWAVE TROUGH MOVING INTO THE WEST...SO A GENERAL MODEL  
COMPROMISE WILL BE PREFERRED.  
 
   
..LONGWAVE TROUGH EVOLUTION INTO THE WESTERN U.S. THROUGH FRI
 
   
..EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT
 
   
..SURFACE LOW DEEPENING OVER SOUTHERN CANADA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH 48 HOURS  
12Z ECMWF...AFTER 48 HOURS  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT THROUGH SATURDAY WITH THE  
EVOLUTION OF THE LONGWAVE TROUGH AND ASSOCIATED COLD FRONT MOVING  
THROUGH THE WESTERN U.S. BUT DIFFERENCES BECOME NOTICEABLE BY  
SUNDAY AS THE ELONGATED N/S TROUGH AXIS ADVANCES ACROSS THE  
PLAINS. THE 00Z GFS BECOMES A BIT OF A STRONGER OUTLIER ON SUNDAY  
WITH ITS HEIGHT FALL EVOLUTION ACROSS SOUTHERN CANADA AND THIS  
RESULTS IN A STRONGER SURFACE LOW COMPARED THE TO THE REMAINING  
GUIDANCE. THE 00Z NAM AND 12Z CMC ALSO TEND TO BE ON THE STRONGER  
SIDE OF THE MODEL SUITE...WITH THE 12Z ECMWF AND 12Z UKMET A BIT  
WEAKER.  
 
OVERALL...THE ENSEMBLE SPAGHETTI PLOTS GENERALLY SUGGEST THE NAM  
AND GFS ARE STILL A TAD TOO STRONG WITH THE NORTHERN PORTION OF  
THE TROUGH AXIS...WITH THE EURO AND CANADIAN MEMBERS STRONGLY  
SUPPORTIVE OF THE OPERATIONAL ECMWF BY 60 HOURS ONWARD. SO BASED  
ON THE LATEST TRENDS AND CLUSTERING...WILL PREFER A GENERAL MODEL  
COMPROMISE THROUGH 48 HOURS...AND THEN FAVOR THE ECMWF THEREAFTER  
WITH THE MASS FIELD DETAILS AT THE SURFACE AND ALOFT.  
 
   
..SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW DEVELOPMENT BY MON
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC CONSENSUS  
CONFIDENCE: AVERAGE  
 
THE MODELS BREAKING AWAY THE SOUTHERN PORTION OF THE LONGER WAVE  
TROUGH EJECTING OUT OF THE WEST AND INTO THE PLAINS STATES ON  
SUNDAY...WITH THIS ENERGY DIGGING SOUTHEAST INTO THE LOWER MS  
VALLEY SUNDAY NIGHT AND RESULTING IN A CLOSED LOW FORMATION BY  
MON. THIS WILL STILL BE INTERACTING WITH THE SOUTHERN PORTION OF A  
N/S ORIENTED FRONTAL ZONE AND THE MODELS SUGGEST A WAVE OF LOW  
PRESSURE WILL DEVELOP ALONG THE BOUNDARY ACROSS PARTS OF THE DEEP  
SOUTH. THE 12Z CMC SOLUTION IS A BIT OF A FASTER AND WEAKER  
OUTLIER WITH THIS SOUTHERN STREAM EVOLUTION...WITH THE 00Z NAM/GFS  
AND 12Z UKMET/ECMWF SOLUTIONS ALL A BIT SLOWER. THE ECMWF IS JUST  
A TAD FARTHER NORTH THAN THE MODEL CONSENSUS BUT IS WELL WITHIN  
THE EURO AND CANADIAN ENSEMBLE SPREAD. THE GFS AND GEFS MEMBERS  
ARE SEEN OVERALL BEING A BIT WEAKER THAN THE ECMWF AND THE EURO  
ENSEMBLE CLUSTER. BASED ON THE LATEST DETERMINISTIC SPREAD...A  
MULTI-MODEL BLEND WILL BE PREFERRED MINUS THE CMC SOLUTION...AND  
THUS A NON-CMC CONSENSUS.  
 
   
..NEXT UPPER TROUGH SWEEPING ACROSS THE NORTHERN PLAINS MON
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODEL ALLOWING ADDITIONAL UPPER TROUGHING TO SWING ACROSS THE  
NORTHERN PLAINS BY SUNDAY NIGHT AND MONDAY ALONG WITH A COLD  
FRONT. THE 12Z UKMET IS A LITTLE FASTER THAN THE MODEL  
CONSENSUS...WITH THE 00Z GFS JUST A TAD SLOWER. THE 00Z NAM/12Z  
CMC AND 12Z ECMWF ARE GENERALLY THE SLOWEST. OVERALL...A CONSENSUS  
OF THE GFS AND ECMWF WOULD TEND TO APPROXIMATE THE MODEL  
CONSENSUS...SO A BLEND OF THESES TWO SOLUTIONS WILL BE PREFERRED.  
 
   
..SHORTWAVE REACHING BRITISH COLUMBIA SAT WITH WARM FRONT
 
   
..NEXT ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-UKMET CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
THE NEXT ATMOSPHERIC RIVER WILL BE IMPACTING THE PACIFIC NORTHWEST  
BY LATER FRIDAY NIGHT AND SATURDAY AS A STRONG PACIFIC JET AND  
EMBEDDED SHORTWAVE ENERGY ARRIVES ALONG WITH A WARM FRONT. THERE  
IS MINIMAL MASS FIELD SPREAD AS THE SYSTEM INITIALLY ARRIVES BY  
SATURDAY. STRONG ONSHORE FLOW IS EXPECTED TO CONTINUE FOR WESTERN  
WA/OR THROUGH EARLY SUNDAY BEFORE THEN SUBSIDING. THE ONLY REAL  
MASS FIELD DIFFERENCE OF NOTE IS WITH THE 12Z UKMET WHICH APPEARS  
BY LATER SATURDAY AND SUNDAY TO BE SHIFTING ITS AXIS OF STRONGER  
ONSHORE FLOW A BIT FARTHER NORTH COMPARED TO THE REMAINING MODELS  
WHICH ARE WELL CLUSTERED. WILL PREFER A NON-UKMET CONSENSUS.  
 
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