958  
FXUS10 KWNH 220424  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1124 PM EST TUE NOV 21 2017  
 
VALID NOV 22/0000 UTC THRU NOV 25/1200 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
00Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
SYSTEM APPROACHING THE WEST COAST SATURDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-GFS BLEND; CONFIDENCE ABOVE AVERAGE  
 
THE 00Z GFS MOVES THIS SYSTEM A BIT QUICKER THAN THE OTHER  
GUIDANCE, WHICH MIGHT BE DUE TO LIMITED CONVECTIVE/GRIDSCALE  
FEEDBACK NOTED IN ITS FRIDAY SOLUTIONS WELL OFFSHORE CA. ALOFT,  
THE FLOW IS BECOMING WELL AMPLIFIED, WHICH SHOULD RESULT EITHER IN  
A SLOWER MOVING SYSTEM OR A SYSTEM WITH LESS AMPLITUDE THAN THE  
GFS IS ADVERTISING. A COMPROMISE OF THE 00Z NAM, 12Z UKMET, 12Z  
CANADIAN, AND 12Z ECMWF IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE.  
 
SLOW MOVING MID-UPPER LEVEL TROUGH ALONG THE GULF COAST  
SURFACE LOWS IN THE EASTERN GULF OF MEXICO/NEAR FLORIDA  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND; CONFIDENCE SLIGHTLY ABOVE AVE  
 
STARTING FRIDAY, THE NAM STARTS DIVERGING FROM THE OTHER GUIDANCE  
IN BECOMING DEEPER/SLOWER ALOFT/MORE WESTERLY AT THE SURFACE WITH  
THIS SYSTEM -- ITS USUAL BIAS AT THIS TIME RANGE. THE 12Z GLOBAL  
ENSEMBLE SPREAD IS NOT LARGE ENOUGH TO CAPTURE THE NAM SOLUTION,  
SO IT IS NOT PREFERRED. THE 00Z GFS SHOWS EVIDENCE OF  
CONVECTIVE/GRIDSCALE FEEDBACK ACROSS FL WHICH DEEPENS ITS LOW AS  
WELL. HOWEVER, ITS SURFACE TRACK RESEMBLES THE OTHER GUIDANCE.  
TO ACCOUNT FOR THE UNCERTAINTY, A COMPROMISE OF THE 00Z GFS, 12Z  
UKMET, 12Z CANADIAN, AND 12Z ECMWF IS PREFERRED WITH SLIGHTLY  
ABOVE AVERAGE CONFIDENCE. FOR QPF CONSIDERATIONS...SEE OUR  
QUANTITATIVE PRECIPITATION DISCUSSION (QPFPFD).  
 
SYSTEM MOVING NEAR/NORTH OF THE US/CANADIAN BORDER  
UPPER TROUGH AFFECTING THE GREAT LAKES/NORTHEAST WED-FRI  
SURFACE LOW MOVING INTO ATLANTIC CANADA  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
THE GUIDANCE SHOWS GOOD AGREEMENT WITH THESE FEATURES. A  
COMPROMISE OF THE 12Z CANADIAN, 12Z UKMET, 00Z NAM, 00Z GFS, AND  
12Z ECMWF IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ROTH  

 
 
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