699  
FXUS10 KWNH 091841  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
240 PM EDT SUN AUG 09 2020  
 
VALID AUG 09/1200 UTC THRU AUG 13/0000 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES AND FORECAST  
CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..LONGWAVE TROUGHING OVER THE NORTHWEST TUESDAY-WEDNESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z GFS BLEND  
CONFIDENCE: AVERAGE  
 
AS A BROAD MID-UPPER LEVEL TROUGH AXIS TRANSLATES EASTWARD FROM  
THE NORTHEASTERN PACIFIC EARLY THIS WEEK, REACHING SOUTHWESTERN  
CANADA AND THE NORTHWESTERN U.S. TUESDAY INTO WEDNESDAY. OF THE  
LATEST GUIDANCE, ONLY THE 12Z GFS STANDS OUT WITH A SLOWER  
PROGRESSION OF A SHORTWAVE INTO WASHINGTON AND OREGON LATE  
WEDNESDAY. FOR NOW, PREFER TO GO TOWARD THE STRONGER CONSENSUS,  
OUTSIDE OF THE 12Z GFS.  
 
...WEAK TROUGHING/SURFACE LOW ALONG THE SOUTHEASTERN U.S. COAST ON  
WEDNESDAY.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS, 12Z ECMWF, 12Z UKMET BLEND  
CONFIDENCE: BELOW AVERAGE  
 
MODEL FORECASTS TAKE AN EXISTING MCV OVER THE LOWER OHIO VALLEY  
FROM SUNDAY MORNING, SOUTHEASTWARD TOWARD THE CAROLINAS BY  
WEDNESDAY MORNING. THE MODELS DIFFER IN STRENGTH REGARDING THIS  
FEATURE WITH MOST DEVELOPING A SURFACE LOW INTO THE SOUTHEAST AND  
NEAR THE COASTLINE. THE ENSEMBLES DEPICT THIS FEATURE RATHER WELL,  
AND WHILE SINGLE MODEL IS AN OUTLIER, THE 12Z NAM IS STRONGEST AND  
12Z CMC LIES ON THE EASTERN EDGE OF THE LATEST SPREAD WHILE ALSO  
LEANING TOWARD THE STRONGER SIDE OF THE GUIDANCE. THE 12Z GFS IS  
WEAKEST BUT A BLEND OF THE GFS WITH THE 12Z ECMWF AND 12Z UKMET  
APPEARS TO BE THE BEST COMPROMISE FOR THIS SYSTEM. CONFIDENCE IS  
LOW GIVEN THE ROLE OF FUTURE CONVECTION IN THE EVOLUTION OF THIS  
FEATURE.  
 
...REMAINDER OF OVERALL WEATHER PATTERN ACROSS THE CONTINENTAL U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND LED BY THE 12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE REMAINDER OF THE U.S. WILL FEATURE QUASI-ZONAL FLOW ACROSS THE  
NORTHERN HALF OF THE NATION WITH A BI-MODAL RIDGE CENTERED OVER  
THE LOWER MISSISSIPPI VALLEY AND SOUTHERN ARIZONA/NEW MEXICO. A  
LARGE CLOSED LOW WILL TRACK EAST ACROSS CANADA WITH SOME WEAKENING  
THROUGH WEDNESDAY. A COLD FRONT WILL FOLLOW AT THE SURFACE WITH  
POTENTIAL FOR CONVECTIVE FLARE UPS NEAR THE FRONTAL BOUNDARY.  
WHILE DIFFERENCES EXIST WITH THE MODELS REGARDING THESE FLARE UPS  
AND THEIR IMPACTS ON THE MID-LEVELS, NO SINGLE MODEL CAN BE RULED  
OUT WITH ANY CONFIDENCE. AT THIS TIME, A GENERAL MODEL BLEND IS  
PREFERRED BUT WITH THE MOST WEIGHT TOWARD THE 12Z GFS AND `1Z  
ECMWF AS THEY ARE CLOSER TO THE MIDDLE OF THE MODEL SPREAD WITH  
FEATURES ACROSS THE REMAINDER OF THE U.S., NOT ALREADY DISCUSSED  
IN THE ABOVE SECTIONS.  
 
THERE WERE NO SIGNIFICANT DIFFERENCES NOTED WITH THE 12Z  
ECMWF/UKMET/CMC COMPARED TO THEIR PREVIOUS 00Z CYCLES.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
THIS PRODUCT WILL TERMINATE AUGUST 15, 2020:  
WWW.WEATHER.GOV/MEDIA/NOTIFICATION/PDF2/SCN20-58PMDHMD_TERMINATION.  
PDF  
 
OTTO  
 

 
 
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