893  
FXUS10 KWNH 151645  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1244 PM EDT WED JUL 15 2020  
 
VALID JUL 15/1200 UTC THRU JUL 19/0000 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...LONG WAVE TROUGH CROSSING THE NORTH CENTRAL US THROUGH THU WITH  
AN ACCOMPANYING SURFACE COLD FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 12Z NAM/GFS ARE CLOSE TO THE MODEL CONSENSUS TAKING THE BROAD  
LONG WAVE TROUGH FROM THE UPPER MS VALLEY THIS AFTERNOON INTO  
WESTERN QUEBEC FRI MORNING, THOUGH THE 12Z GFS MIGHT BE A BIT  
FASTER THAN THE CONSENSUS AT THIS POINT. THERE IS ALSO GOOD  
CLUSTERING WITH THE TIMING OF THE ASSOCIATED SURFACE COLD FRONT,  
THOUGH THE 12Z GFS MIGHT BE A BIT FASTER THAN THE CONSENSUS  
REACHING THE NORTHEAST FRI AFTERNOON.  
 
HOWEVER, NONE OF THE MODEL DIFFERENCES WERE SIGNIFICANT ENOUGH TO  
KEEP THEM OUT OF THE PREFERRED BLEND. DUE TO THE GOOD CLUSTERING,  
FORECAST CONFIDENCE HAS INCREASED WITH THIS MODEL CYCLE.  
 
   
..CUT OFF LOW WEST OF CALIFORNIA BY THURSDAY MORNING
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
BOTH THE 12Z NAM/GFS ARE CLOSE TO THE MODEL CONSENSUS WITH THE  
DEVELOPMENT OF A CLOSED MID LEVEL LOW JUST OFF THE SOUTHWESTERN CA  
COAST LATE THU INTO EARLY FRI. THEY ARE ALSO CLOSE WITH TAKING THE  
MID LEVEL SYSTEM WEST INTO THE PACIFIC WITH TIME. SINCE PLACEMENT  
AND TIMING DIFFERENCES ARE FAIRLY MINOR, A GENERAL MODEL BLEND IS  
PREFERRED WITH THIS SYSTEM.  
 
...LONG WAVE TROUGH CROSSING THE PACIFIC NORTHWEST THU, MOVING  
INTO SOUTH CENTRAL CANADA BY SAT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z NAM BLEND  
CONFIDENCE: AVERAGE  
 
THERE IS GENERALLY MODEL MODEL CLUSTERING WITH THE LONG WAVE  
TROUGH THAT CROSSES THE PACIFIC NORTHWEST THU MORNING. AS THE  
TROUGH MOVES INTO MANITOBA/SASKATCHEWAN SAT INTO SUN, MODEL SPREAD  
DEVELOPS WITH RESPECT TO TIMING. WHILE ALL OF THE MOST RECENT  
MODEL SOLUTIONS SLOW THE TROUGH AS IT REACHES CENTRAL CANADA, THE  
12Z NAM CONTINUES IT'S MODEL TREND OF BEING SLOWER THAN THE  
CONSENSUS, ESPECIALLY BY 12Z SUN.  
 
A COLD FRONT ASSOCIATED WITH THE TROUGH EXTENDS FROM THE UPPER MS  
VALLEY INTO THE CENTRAL PLAINS BY THAT TIME. AGAIN, THE 12Z NAM IS  
SLOWER WITH THE FRONT; OTHERWISE THERE IS GOOD CLUSTERING WITH THE  
PLACEMENT OF THE FRONT BY THE END OF THE PERIOD. BASED ON THE  
ABOVE, A NON 12Z NAM BLEND IS PREFERRED. DUE TO THE INCREASE IN  
SPREAD ACROSS CENTRAL CANADA WITH THE LONG WAVE TROUGH, FORECAST  
CONFIDENCE IS ONLY AVERAGE.  
 
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  
 
HAYES  
 

 
 
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