151  
FXUS10 KWNH 171632  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1232 PM EDT TUE OCT 17 2017  
 
VALID OCT 17/1200 UTC THRU OCT 21/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS MODEL EVALUATION WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
...UPPER TROUGH DIGGING INTO THE PACIFIC NORTHWEST WEDNESDAY NIGHT  
WITH ASSOCIATED ATMOSPHERIC RIVER EVENT...   
..TROUGH/COLD FRONT REACHING THE PLAINS ON FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM / 00Z ECMWF BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
DIFFERENCES IN THE GUIDANCE ARE MINOR UNTIL THE UPPER TROUGH AXIS  
MOVES OVER THE INTERMOUNTAIN WEST ON FRI. ENSEMBLES HAVE BEEN  
TRENDING SLIGHTLY FASTER WITH THE UPPER TROUGH AXIS VALID FRIDAY  
EVENING BUT THE 12Z GFS IS AT THE FAR LEADING EDGE OF THE LATEST  
ENSEMBLE GUIDANCE...AND IS CONSIDERED TOO FAST. UPSTREAM FLOW IS  
AMPLIFYING SO FASTER SOLUTIONS LIKE THE GFS ARE LESS PREFERRED. A  
SOLUTION TOWARD THE MIDDLE OF THE LATEST ENSEMBLE  
GUIDANCE...REPRESENTED BY A 12Z NAM / 00Z ECMWF BLEND IS  
RECOMMENDED HERE.  
 
...SHORTWAVE MOVING QUICKLY ALONG THE U.S.-CANADA BORDER THROUGH  
THU WITH ASSOCIATED DEEPENING SURFACE LOW AND COLD FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z UKMET BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN DECENT AGREEMENT BUT THE 00Z UKMET STANDS OUT AS  
SLOWEST OF THE LATEST DETERMINISTIC GUIDANCE. GIVEN THE ENSEMBLE  
MEANS ARE AHEAD OF THE 00Z UKMET AND THE ZONAL FLOW PROMOTES  
FASTER PROGRESSION WITH THIS SYSTEM...A NON 00Z UKMET BLEND IS  
RECOMMENDED.  
 
...UPPER LEVEL TROUGH AXIS CROSSING THE SRN ROCKIES INTO THE  
PLAINS ON FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
MINOR AMPLITUDE/TIMING DIFFERENCES EXIST WITH THIS SYSTEM...WITH A  
12Z GFS AND 00Z ECMWF BLEND DOWN THE MIDDLE OF THESE DIFFERENCES.  
 
...LINGERING BROAD TROUGH OVER THE SOUTHEAST STATES WITH SLOW  
MOVING COLD FRONT IN THE VICINITY OF FLORIDA...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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