759  
FXUS10 KWNH 111627  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1226 PM EDT SUN AUG 11 2019  
 
VALID AUG 11/1200 UTC THRU AUG 15/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
THROUGH WEDNESDAY, THE SYNOPTIC FLOW WILL TRANSITION FROM A  
MIDDLE-CONUS RIDGE, TO NEARLY ZONAL FLOW, TO A WESTERN  
RIDGE/EASTERN TROUGH BY THE END OF THE FORECAST PERIOD. WHILE THE  
GUIDANCE IS NEARLY UNIFORM IN DEVELOPING THIS EVOLUTION, THERE IS  
STILL SOME TEMPORAL DEPTH VARIANCE OF THE EVOLUTION AMONG THE  
MODELS.  
 
INITIALLY, A CLOSED LOW MOVING ACROSS THE NORTHWEST AND A  
SHORTWAVE MOVING NORTHEAST THROUGH THE FOUR CORNERS REGION WILL  
WORK IN TANDEM TO FLATTEN THE RIDGE INTO A MORE ZONAL PATTERN. THE  
12Z NAM REMAINS STRONGER THAN THE REASONABLY WELL CLUSTERED GLOBAL  
MODELS WITH THE ENERGY THAT TRAVERSES THE NORTHERN PLAINS AND NEAR  
THE CANADIAN BORDER, ALTHOUGH IT COMES INTO SOMEWHAT BETTER  
AGREEMENT AS THE ENERGY DIGS EAST-SOUTHEAST ACROSS THE GREAT LAKES  
REGION AND NORTHEAST BY LATER TUESDAY AND WEDNESDAY. SIMILARLY  
DURING THIS TIME, THE 00Z UKMET CONTINUES ITS SUMMER-LONG TREND OF  
BEING GENERALLY TOO STRONG WITH THE MID-LEVEL RIDGE, IN THIS CASE  
KEEPING THE 594DM HEIGHTS WELL LONGER THAN ANY OTHER GUIDANCE. THE  
UKMET IS ALSO THE WEAKEST OF ALL THE SOLUTIONS WITH THE ENERGY  
DIGGING ACROSS THE UPPER MIDWEST, GREAT LAKES AND THE BROADER  
EASTERN U.S. TOWARD THE END OF THE PERIOD.  
 
THE SHORTWAVE ENERGY DIGGING EAST-SOUTHEAST ACROSS THE MIDWEST AND  
INTO THE EAST WILL DRIVE A COLD FRONT EASTWARD THROUGH THE PERIOD  
ALONG WITH A WELL-DEFINED WAVE OF LOW PRESSURE THAT INITIALLY  
DEVELOPS OVER THE CENTRAL HIGH PLAINS IN RELATION TO THE SHORTWAVE  
EXITING THE FOUR CORNERS REGION. THIS LOW WILL CROSS THROUGH THE  
MIDWEST ON MONDAY, AND THEN ADVANCE PROGRESSIVELY UPPER OHIO  
VALLEY, NORTHERN MID-ATLANTIC AND SOUTHERN NEW ENGLAND THROUGH  
TUESDAY. AS THE LOW ADVANCES ACROSS SOUTHERN NEW ENGLAND, THE 12Z  
NAM BECOMES A STRONGER OUTLIER, AND ACCORDINGLY HAS A MUCH WETTER  
QPF SOLUTION OVER THE NORTHERN MID-ATLANTIC AND SOUTHERN NEW  
ENGLAND. THE 00Z UKMET FOR ITS PART APPEARS TO BE TOO PROGRESSIVE  
WITH THE WAVE EVOLUTION ALL THE WAY FROM THE CENTRAL PLAINS TO THE  
EAST COAST WHICH IS LIKELY TIED INTO ITS LESS-AMPLIFIED SHORTWAVE  
ENERGY. THE 12Z GFS TENDS TO BE A LITTLE STRONGER THAN THE  
MULTI-MODEL CONSENSUS BY THE END OF THE PERIOD ACROSS THE EAST  
WITH THE LARGER SCALE TROUGH AMPLIFICATION, BUT IT HAS TRENDED IN  
THIS DIRECTION, AND THERE IS SOME ENSEMBLE SUPPORT FOR THIS FROM  
THE ECENS AND GEFS SUITES. ALL OF THE MODELS FAVOR A TRAILING COLD  
FRONT CROSSING THE MIDWEST AND GRADUALLY SLOWING DOWN AS IT MOVES  
INTO THE MID-ATLANTIC AND SOUTHEAST BY THE END OF THE PERIOD. IN  
THE WAKE OF THE LEAD WAVE EXITING SOUTHERN NEW ENGLAND, ADDITIONAL  
WAVES OF LOW PRESSURE ARE LIKELY TO DEVELOP ALONG THE FRONT BY THE  
END OF THE PERIOD OVER THE INTERIOR OF THE MID-ATLANTIC AND THE  
SOUTHEAST IN RESPONSE TO THE LARGER SCALE TROUGH AMPLIFICATION  
BEGINNING TO TAKE SHAPE.  
 
OVERALL, THE ENSEMBLE GUIDANCE FAVORS A SOLUTION HEAVILY WEIGHTED  
TOWARD A CONSENSUS OF THE 12Z GFS AND 00Z ECMWF, AND ESPECIALLY AT  
THE SURFACE, SO FOR THE TIME BEING, A BLEND OF THE GFS AND ECMWF  
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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