676  
FXUS10 KWNH 051845  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 PM EST SUN NOV 05 2017  
 
VALID NOV 05/1200 UTC THRU NOV 09/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH FINAL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE ROTATING THROUGH EASTERN CANADA THROUGH MONDAY WITH  
TRAILING COLD FRONT FROM GREAT LAKES/NORTHEAST TO SOUTHERN  
PLAINS...   
..STALLING FRONT OVER THE SOUTHERN U.S. TUESDAY AND WEDNESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z ECMWF / 12Z UKMET  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS GENERALLY SHOW EXCELLENT AGREEMENT WITH THIS ENTIRE  
SYSTEM THROUGH THE FIRST 24 HOURS...BOTH WITH THE SHORTWAVE AND  
THE NORTHERN PORTION OF THE FRONT PROPAGATING MORE QUICKLY EAST  
ACROSS THE NORTHERN LATITUDES...AND THE STALLING FRONT ACROSS THE  
SOUTH ACCOMPANIED BY ZONAL FLOW ALOFT. HOWEVER...THERE ARE SOME  
DIFFERENCES THAT BEGIN TO EMERGE AS THE FRONT STALLS ACROSS THE  
SOUTHERN U.S. THE 12Z NAM AND 00Z CMC (AT SLIGHTLY DIFFERENT  
TIMES) DEVELOP A SURFACE LOW OVER THE SOUTHEAST AND THEN MOVE IT  
OUT OFF THE MID-ATLANTIC COAST WITH CONTINUED DEEPENING. THE OTHER  
GLOBAL MODELS DO HINT AT SOME WEAK SURFACE LOW DEVELOPMENT IN THE  
VICINITY OF THE COASTAL CAROLINAS BY WEDNESDAY...BUT NEVER DEEPEN  
IT SUBSTANTIALLY. THIS SEEMS MORE LIKELY GIVEN THE FAIRLY ZONAL  
FLOW PATTERN. GIVEN THE EFFECTS OF THE SURFACE LOW DEVELOPMENT ON  
SENSIBLE WEATHER ACROSS THE SOUTHERN U.S....THE PREFERENCE IS FOR  
A BLEND OF THE GFS...ECMWF...AND UKMET BASED ON THEIR FAIRLY GOOD  
AGREEMENT ON THE MASS FIELDS.  
 
18Z UPDATE: NO CHANGE FROM THE INITIAL PREFERENCE. THE 12Z CMC HAS  
TRENDED AWAY FROM ITS SURFACE LOW DEVELOPMENT IN THE  
SOUTHEAST...BUT STILL SHOWS LOWER SURFACE PRESSURES THAN THE OTHER  
GLOBAL MODELS. AS A RESULT...THE INITIAL PREFERENCE OF A  
GFS...ECMWF...UKMET BLEND WILL BE MAINTAINED.  
 
...POSITIVELY TILTED TROUGH TRANSLATING FROM THE PACIFIC NORTHWEST  
TODAY TO THE PLAINS BY WEDNESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z ECMWF / 12Z UKMET  
CONFIDENCE: AVERAGE  
 
AS THE POSITIVELY TILTED TROUGH PUSHES THROUGH THE WESTERN  
STATES...THE 00Z CMC DEAMPLIFIES THE WAVE FASTER THAN THE OTHER  
GLOBAL MODELS...AND ALSO BUILDS IN THE UPSTREAM RIDGE MORE  
RAPIDLY. THE RESULT IS A WEAKER WAVE THAT BEGINS TO ACCELERATE  
INTO THE PLAINS MUCH FASTER THAN OTHER AVAILABLE MODELS. THIS MAY  
CONTRIBUTE TO ITS DEVELOPMENT OF A SURFACE LOW OVER THE SOUTHEAST  
ON WEDNESDAY...DISCUSSED IN THE ABOVE SECTION. THIS SOLUTION IS  
ENOUGH OF AN OUTLIER FOR IT TO BE EXCLUDED FROM THE PREFERENCE.  
THE 12Z NAM IS AN OUTLIER IN THE OPPOSITE MANNER...WITH A STRONGER  
WAVE OVER THE PLAINS BY WEDNESDAY...AND IT WAS ALSO EXCLUDED.  
FINALLY...THE 00Z UKMET WAS MUCH STRONGER WITH A SECONDARY  
SHORTWAVE OVER THE EASTERN PACIFIC...THAT IT EVENTUALLY TRACKS  
INTO THE DESERT SOUTHWEST AS THE OTHER TROUGH BEGINS TO REACH THE  
CONTINENTAL DIVIDE. THE DOWNSTREAM RIDGING INDUCED BY THE STRONGER  
SHORTWAVE OVER THE SOUTHWEST APPEARS TO LEAD TO A FLATTER WAVE  
OVER THE PLAINS THAT GETS SHEARED OUT IN A WAY THAT IS  
INCONSISTENT WITH THE OTHER MODELS. UNTIL THERE IS MORE SUPPORT  
FOR A STRONGER SECONDARY WAVE OVER THE DESERT SOUTHWEST...THE  
UKMET IS ALSO EXCLUDED FROM THE PREFERENCE FOR THIS SYSTEM.  
THEREFORE...A BLEND OF THE GFS AND ECMWF IS PREFERRED.  
 
18Z UPDATE: ADDED THE UKMET TO THE PREFERENCE. THE 12Z UKMET HAS  
TRENDED WEAKER WITH THE SECONDARY WAVE MOVING INTO THE DESERT  
SOUTHWEST...AND AS A RESULT HAS A MORE REALISTIC DEPICTION OF THE  
POSITIVE TILT TROUGH AS IT PUSHES INTO THE PLAINS (MUCH CLOSER TO  
THE GFS AND ECMWF AS WELL). THE 12Z CMC HAS TRENDED IN THE  
DIRECTION OF THE GFS AND ECMWF AS WELL...BUT IT IS STILL FASTER  
WITH THE TROUGH AND AN OUTLIER.  
 
...DEEP CYCLONE DROPPING FROM THE GULF OF ALASKA TO OFFSHORE OF  
THE PACIFIC NORTHWEST BY WEDNESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND 12Z ECMWF / 12Z GFS / 00Z ECMWF ENS / 12Z GEFS  
CONFIDENCE: AVERAGE  
 
MODELS ARE OVERALL IN FAIRLY GOOD AGREEMENT WITH THIS SYSTEM BUT  
SOME DIFFERENCES IN PLACEMENT OF THE LOW BEGIN TO EMERGE BY  
WEDNESDAY. TO ACCOUNT FOR THIS SPREAD IN PLACEMENT...THE  
PREFERENCE IS TO BLEND IN SOME OF THE ENSEMBLE MEANS (ECMWF AND  
GEFS). THE OPERATIONAL MODEL THAT IS CLOSEST TO THESE ENSEMBLE  
MEANS IS THE 00Z ECMWF...SO THAT WAS ALSO INCORPORATED INTO THE  
PREFERENCE.  
 
THE 00Z UKMET AND 00Z CMC MOST AGGRESSIVELY AMPLIFY THE DOWNSTREAM  
RIDGE OVER THE WESTERN U.S. LATE ON TUESDAY...AND ARE NEAR THE  
EXTREME IN THE ENSEMBLE SPREAD. THE 00Z UKMET AND 12Z NAM ARE ALSO  
MORE EXPANSIVE WITH THE SIZE OF THE LOW OVER THE NORTHEAST PACIFIC  
THAN THE OTHER MODELS. AS A RESULT...THE PREFERENCE WAS WEIGHTED  
AWAY FROM THESE SOLUTIONS AND TOWARD MORE LIKELY SCENARIOS BASED  
ON ENSEMBLE CLUSTERING.  
 
18Z UPDATE: THE 12Z GFS AND 12Z GEFS MEAN APPEAR CLOSE ENOUGH TO  
THE ECMWF SOLUTIONS TO BE INCORPORATED INTO THE PREFERENCE FOR  
THIS SYSTEM. GIVEN THE CONTINUED DETAIL DIFFERENCES...PREFER TO  
CONTINUE TO USE ENSEMBLES IN THE PREFERENCE.  
 
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