092  
FXUS10 KWNH 140823  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
422 AM EDT FRI AUG 14 2020  
 
VALID AUG 14/0000 UTC THRU AUG 17/1200 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
 
...LONG WAVE TROUGH MOVING FROM THE NORTHWEST TO THE WESTERN GREAT  
LAKES...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON GFS OR UKMET  
CONFIDENCE: AVERAGE  
 
LONGWAVE TROUGH MOVING ACROSS THE NORTHERN TIER WILL BE REINFORCED  
BY A POTENT VORTICITY MAXIMA ROTATING THROUGH THE BASE OF THIS  
TROUGH AND INTO THE WESTERN GREAT LAKES SATURDAY, WITH A SECONDARY  
VORT LOBE DRIVING EASTWARD QUICKLY ON ITS HEELS SUNDAY. THE  
GLOBALS ARE OVERALL IN VERY GOOD AGREEMENT BOTH WITH POSITION AND  
INTENSITY OF THIS LEAD SHORTWAVE, BUT THE GFS CONTINUES TO EXHIBIT  
A PROGRESSIVE BIAS AND OUTRUNS THE CONSENSUS EARLY IN THE FORECAST  
PERIOD. WHILE THE OTHER GUIDANCE SEEMS TO HAVE SPED UP A BIT, THE  
GFS BEING ON THE FAST EDGE OF THE ENVELOPE MAKES IT AN OUTLIER AND  
THE PREFERENCE DOES NOT INCLUDE IT. THE UKMET, WHILE IT IS SIMILAR  
TO THE OTHERS WITH THE INTENSITY OF THIS LEAD IMPULSE, ITS BIAS OF  
BEING TOO STRONG WITH RIDGES SHOWS UP WHICH CAUSES A LATITUDINAL  
POSITION NORTH OF THE OTHER GUIDANCE AND IS ALSO NOT PREFERRED.  
 
THE SECOND SHORTWAVE AND ASSOCIATED SENSIBLE WEATHER WILL BE  
HIGHLY DEPENDENT ON THE EFFECTS OF THE FIRST, WITH THE LINGERING  
INFLUENCE DRIVING POSITION AND INTENSITY CHANGES IN THE ASSOCIATED  
CONVECTION BENEATH THE SECOND SHORTWAVE. FOR CONSISTENCY, A BLEND  
WHICH DOES NOT CHANGE FROM THE FIRST SHORTWAVE SEEMS MOST  
REASONABLE AS SMALL SCALE INTERACTIONS FROM THUNDERSTORMS ARE  
DIFFICULT TO RESOLVE EVEN BY D2.  
 
   
..LONGWAVE TROUGH ACROSS THE EASTERN CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-ECMWF/UKMET  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
ALTHOUGH THE OVERALL SPREAD IS PRETTY SMALL IN THE AMPLITUDE OF  
THE TROUGH DIGGING INTO THE GULF COAST THIS WEEKEND, THERE IS MUCH  
MORE VARIABILITY IN THE SECONDARY TROUGH MOVING THROUGH THE OHIO  
VALLEY AND HOW IT IMPACTS SURFACE LOW DEVELOPMENT BY SUNDAY MOVING  
ACROSS THE MID-ATLANTIC. THE ECMWF REMAINS AN OUTLIER AND IS  
COMPLETELY OUT OF PHASE (SHORTWAVE RIDGE VS. SHORTWAVE TROUGH) IN  
THE OH VLY SATURDAY AFTN BEFORE EVENTUALLY FORMING A LAGGING  
TROUGH. OTHERWISE, THE DETERMINISTIC GUIDANCE IS IN PRETTY CLOSE  
AGREEMENT WITH THE MID-LEVEL FEATURE, ALTHOUGH THE GEFS MEAN IS A  
BIT DEEP COMPARED TO THE CONSENSUS, AND THE UKMET CONTINUES TO  
FEATURE HEIGHTS ABOVE THE REST OF THE MODELS EVEN WITHIN THE  
TROUGH. THE GFS MAY BE A BIT FAST TO PUSH THE ACCOMPANYING SURFACE  
LOW TO THE NORTHEAST, AND A SUBTLY LOWER BLEND NEAR THE NAM/CMC  
COULD BE A REASONABLE SOLUTION, BUT INTERACTION WITH A WAVE OFF  
NORTH CAROLINA THE MORNING, AND POTENTIAL MCVS DIVING INTO THE  
TROUGH THROUGH THE WEEKEND WILL ALL IMPACT THE EVOLUTION OF BOTH  
SURFACE AND MID-LEVEL FEATURES. THIS LEAVES LOWER THAN AVERAGE  
CONFIDENCE, AND SOMETHING BETWEEN THE FASTEST GFS AND SLOWER  
GEFS/ECMWF IS PROBABLY MOST REALISTIC AT THIS TIME.  
 
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  
 
WEISS  
 

 
 
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