851  
FXUS10 KWNH 210423  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1123 PM EST MON NOV 20 2017  
 
VALID NOV 21/0000 UTC THRU NOV 24/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
SYSTEM MOVING BY THE NORTHWEST ALONG THE US/CAN BORDER THU  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND; CONFIDENCE ABOVE AVERAGE  
 
THE 00Z NAM BECOMES A SLOW/DEEP OUTLIER WITH THIS SYSTEM, ITS  
USUAL BIAS ON DAY 3. THE FLOW IN WHICH THE SYSTEM IS EMBEDDED --  
SUPERGEOSTROPHIC OVER THE TOP OF A RIDGE -- FAVORS A PROGRESSIVE  
SYSTEM. A COMPROMISE OF THE 00Z GFS, 12Z ECMWF, 12Z UKMET, AND  
12Z CANADIAN IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE.  
 
TROUGHING ACROSS THE GREAT LAKES/NORTHEAST  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE TWO SYSTEMS EMBEDDED WITHIN THIS TROUGH SHOW GOOD AGREEMENT  
OVER THE NEXT FEW DAYS. A COMPROMISE OF THE 00Z GFS, 00Z NAM, 12Z  
ECMWF, 12Z UKMET, AND 12Z CANADIAN IS FAVORED WITH ABOVE AVERAGE  
CONFIDENCE.  
 
TROUGH AMPLIFYING AS IT EDGES THROUGH THE GULF OF MEXICO  
SURFACE LOWS IN THE EASTERN GULF OF MEXICO/NEAR FLORIDA  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND; CONFIDENCE SLIGHTLY ABOVE AVE  
 
STARTING TUESDAY EVENING, THE NAM STARTS DIVERGING FROM THE OTHER  
GUIDANCE IN BECOMING DEEPER/SLOWER ALOFT WITH THIS SYSTEM -- ITS  
USUAL DAY 3 BIAS. CONSIDERING THE BROAD AND FLATTENING RIDGING  
UPSTREAM, A BROADER/SLIGHTLY MORE PROGRESSIVE SOLUTION SIMILAR TO  
A COMPROMISE OF THE 00Z GFS, 12Z CANADIAN, 12Z UKMET, AND 12Z  
ECMWF MAKES SENSE MASS FIELD-WISE. FOR QPF CONSIDERATIONS, SEE  
OUR QUANTITATIVE PRECIPITATION DISCUSSION (QPFPFD).  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ROTH  

 
 
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