020  
FXUS10 KWNH 150636  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
235 AM EDT THU AUG 15 2019  
 
VALID AUG 15/0000 UTC THRU AUG 18/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION...WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z GEFS/12Z ECENS MEAN BLEND...NORTH-CENTRAL U.S.  
NON-NAM BLEND...REMAINDER OF CONUS  
CONFIDENCE: AVERAGE  
 
THE UPPER-LEVEL PATTERN STARTS OFF WITH STRONG RIDGING ACROSS THE  
SOUTHWEST AND NORTHWESTERLY FLOW TO ITS NORTH, LEADING TO BROAD  
TROUGHING ACROSS THE EASTERN HALF OF THE NATION. THE RIDGE BECOMES  
SUPPRESSED ON FRIDAY AND INTO THE WEEKEND AS UPPER-LEVEL TROUGHING  
BEGINS TO IMPINGE UPON THE NORTHWEST, LEADING TO BROAD QUASI-ZONAL  
FLOW FROM THE PACIFIC NORTHWEST TO THE NORTHEAST.  
 
ANOMALOUS MOISTURE WILL REMAIN IN PLACE AHEAD OF A SLOW MOVING  
FRONT WHICH WILL EXTEND FROM THE MID-ATLANTIC REGION TO THE GULF  
COAST, WHILE IMPULSES IN NORTHWEST FLOW ALOFT KEEP THE CENTRAL  
PLAINS TO THE MIDWEST ACTIVE WITH ORGANIZED CONVECTION. THERE IS  
BROAD AGREEMENT AMONG THE GLOBAL MODELS WITH THE SYNOPTIC SCALE  
FEATURES ACROSS THESE TWO AREAS, BUT THE 00Z NAM IN GENERAL  
APPEARS TO BE TOO AMPLIFIED AND THEREFORE TOO WET WITH THE ENERGY  
IT HAS DIGGING DOWN ACROSS THE MIDWEST AND INTO THE EASTERN U.S.  
THROUGH THE PERIOD. ACROSS THE SOUTHEAST AND EASTERN GULF COAST  
REGION, THE GUIDANCE CONTINUES TO HINT AT A WEAK AREA OF LOW  
PRESSURE DEVELOPING ALONG THE AFOREMENTIONED FRONT. THE 12Z ECMWF  
IN PARTICULAR WAS A STRONG OUTLIER WITH THIS FEATURE AS IT  
APPEARED TO BE SUFFERING FROM CONVECTIVE GRIDSCALE FEEDBACK. THE  
00Z ECMWF HAS TRENDED AWAY FROM THIS SOLUTION AND NOW APPEARS TO  
BE MUCH MORE REASONABLE AND IN AGREEMENT WITH THE REMAINING  
GUIDANCE.  
 
THE GUIDANCE IS REFLECTING SOME OF ITS BIGGEST DISAGREEMENTS WITH  
THE TROUGHING/CLOSED LOW ENERGY ADVANCING THROUGH SOUTH-CENTRAL  
CANADA THIS WEEKEND WHICH IMPACTS THE EVOLUTION OF A COLD FRONT  
ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST. THE 00Z NAM IS  
NOTABLY FARTHER NORTH WITH ITS TRACK OF THE CLOSED LOW, AND IS  
FARTHER NORTH WITH ITS SURFACE LOW FEATURE AS A RESULT. THE NAM  
LEANS ON THE SLOWER SIDE OF THE GUIDANCE WITH ITS FRONTAL  
EVOLUTION, BUT THE 00Z CMC/UKMET AND 00Z ECMWF ARE ALL ALSO NOW  
COLLECTIVELY SLOWER. MEANWHILE, THE 00Z GFS IS THE FASTEST  
SOLUTION WITH ITS HEIGHT FALLS AND THE SURFACE FRONT. THE 00Z GEFS  
MEAN AND 12Z ECENS MEAN BOTH SUGGEST THE GFS IS A FAST OUTLIER,  
BUT THEY ARE A TAD FASTER THAN THE NON-NCEP MODEL CONSENSUS.  
THEREFORE, A PREFERENCE TOWARD A BLEND OF THE ENSEMBLE MEANS WILL  
AGAIN BE PREFERRED AS THEY ARE CLUSTERED FAIRLY WELL WITH EACH  
OTHER.  
 
ELSEWHERE, THE MODELS ACTUALLY SHOW REASONABLY GOOD MODEL MASS  
FIELD AGREEMENT BY THE END OF THE PERIOD WITH RESPECT TO STRONG  
HEIGHT FALLS DROPPING DOWN ACROSS WESTERN CANADA, ALTHOUGH THE 00Z  
NAM IS LIKELY A TAD TOO STRONG WITH ITS CLOSED LOW FEATURE.  
 
BASED ON THE CURRENT GUIDANCE, A NON-NAM BLEND WILL BE PREFERRED  
ACROSS THE CONUS, WITH EXCEPTION TO THE NORTH-CENTRAL U.S. WHERE A  
BLEND OF THE 00Z GEFS MEAN AND 12Z ECENS MEAN WILL BE PREFERRED.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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