172  
FXUS10 KWNH 101710  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
109 PM EDT MON AUG 10 2020  
 
VALID AUG 10/1200 UTC THRU AUG 14/0000 UTC  
 
...SEE NOUS42 KWNO (ADMSDM) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES AND  
FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...LONGWAVE TROUGHING OVER THE NORTHWEST FROM TUESDAY THROUGH  
THURSDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z NAM BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THROUGH THE MIDDLE OF THE WEEK, THE MODEL CONSENSUS IS FOR A  
LONGWAVE TROUGH TO AMPLIFY AS IT REACHES WESTERN CANADA INTO THE  
NORTHWESTERN U.S. THE 12Z NAM IS THE FASTEST OF THE DETERMINISTIC  
GUIDANCE TO PROGRESS THE TROUGH EASTWARD, NOTED WEDNESDAY INTO  
THURSDAY AND THE NAM ALSO LIES ON THE FASTER EDGE OF THE LATEST  
ENSEMBLE GUIDANCE. AMPLIFIED FLOW UPSTREAM SHOULD TEND TO LIMIT A  
FASTER PROGRESSION DEPICTED BY THE NAM AND EVEN TRENDS IN THE  
ENSEMBLES HAVE BEEN SLOWER OVER THE PAST FEW CYCLES.  
 
   
..REMAINDER OF THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND, LEAST WEIGHT ON THE 12Z NAM  
CONFIDENCE: AVERAGE  
 
THERE IS WEAK LOW TO MID-LEVEL TROUGHING IN PLACE OVER THE  
SOUTHEASTERN U.S. TODAY, DOWNSTREAM OF A LOW TO MID-LEVEL RIDGE  
OVER THE LOWER MISSISSIPPI VALLEY. THERE IS A SECONDARY AREA OF  
RIDGING LOCATED OVER THE SOUTHERN AZ/NM BORDER, FORECAST TO EXPAND  
AND SLOWLY LIFT NORTHWEST THROUGH THURSDAY. UP NORTH,  
QUASI-AMPLIFIED FLOW ACROSS THE NORTHERN U.S. INTO SOUTHERN CANADA  
WILL IMPACT THE MOVEMENT OF A COUPLE OF COLD FRONTS INTO THE U.S.  
THERE IS FAIRLY GOOD AGREEMENT ON A DEPARTING MID-UPPER LEVEL  
TROUGH AXIS FROM SOUTHEASTERN CANADA AND THE ATTENDANT COLD FRONT  
INTO THE GREAT LAKES AND NORTHEAST, WHICH EXTENDS WESTWARD THROUGH  
THE OH VALLEY INTO THE GREAT PLAINS.  
 
THE GREATEST DISAGREEMENTS ARE WITH SMALL SCALE, CONVECTIVELY  
DRIVEN VORTICITY MAXIMA WHICH MOVE AND AMPLIFY/DEAMPLIFY WITHIN  
THE RELATIVELY WEAK STEERING CURRENTS OVER THE CENTRAL AND EASTERN  
SECTIONS OF THE COUNTRY. WHILE NO MODELS APPEAR AS AN OUTLIER  
COMPARED TO ENSEMBLE SPAGHETTI PLOTS, THE 12Z NAM APPEARS TOO  
STRONG, ESPECIALLY WITH A MID-LEVEL SHORTWAVE/VORTICITY MAX  
FORECAST TO BE OVER MO/IA THURSDAY MORNING. OVER-AMPLIFICATION OF  
MESOSCALE FEATURES CAN BE A COMMON BIAS IN THE NAM, SO FOR NOW,  
LESS NAM WEIGHTING IS PREFERRED WITHIN A GENERAL MODEL BLEND  
ACROSS THE REMAINDER OF THE CONUS (OUTSIDE OF THE NORTHWEST TROUGH  
DISCUSSED IN THE TOP SECTION).  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page