401  
FXUS10 KWNH 231624  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1223 PM EDT MON OCT 23 2017  
 
VALID OCT 23/1200 UTC THRU OCT 27/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z GFS/NAM EVALUATION LATEST PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
FAST MOVING SYSTEM DIGGING INTO MN LATE THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GFS/ECMWF/UKMET BLEND; CONFIDENCE ABOVE AVERAGE  
 
A STRONG CLOSED HIGH OFFSHORE THE PACIFIC NORTHWEST SHOULD LEAD TO  
AN AMPLIFYING TROUGH MID-CONTINENT. THIS ARGUES AGAINST THE MORE  
OPEN/PROGRESSIVE 00Z CANADIAN AND MORE NORTHERLY 12Z NAM. A  
COMPROMISE OF THE 12Z GFS, 00Z ECMWF, AND 00Z UKMET IS PREFERRED  
WITH ABOVE AVERAGE CONFIDENCE.  
 
MERGING SYSTEMS NEAR THE GREAT LAKES MONDAY NIGHT  
EJECTING EASTERN TROUGH THURSDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: TOWARDS 00Z ECMWF; CONFIDENCE BELOW AVERAGE  
 
THE GUIDANCE IS QUITE AGREEABLE UNTIL TUESDAY MORNING. ON  
WEDNESDAY, THE 12Z NAM BECOMES LOW/DEEP ALOFT WITH THE MAIN SYSTEM  
THOUGH A LEADING SHORTWAVE MOVES THE MOISTURE AXIS MORE EASTWARD  
INTO NEW ENGLAND. SINCE THIS IS NOT BEING DRIVEN BY CONVECTIVE  
FEEDBACK ON THE NAM, IT IS PLAUSIBLE AT THIS POINT. BY WEDNESDAY  
NIGHT, THE NAM BECOMES UNUSABLY SLOW AS THE SYSTEM SHOULD BE  
ACCELERATING NORTHEAST WITHIN SOUTHWESTERLY FLOW WHICH IS SPEEDING  
UP AHEAD OF THE NORTHERN PLAINS SYSTEM. HOWEVER, THE 12Z GFS  
OUTPACES ITS 06Z ENSEMBLE MEAN BY THEN, CLUSTERING WITH THE 00Z  
UKMET (WHICH IS USUALLY TOO FAST) AND THE 00Z CANADIAN. THE 00Z  
CANADIAN TRIES CLOSING OFF A MID-LEVEL CYCLONE IN EASTERN NC, NOT  
SEEN ON THE OTHER GUIDANCE LATE THURSDAY SO DID NOT DEEM ITS  
SOLUTION PLAUSIBLE. AFTER COORDINATION WITH THE QPF AND MEDIUM  
RANGE DESKS, WHICH AGREES BETTER WITH THE ENSEMBLE MEAN SOLUTIONS,  
BELIEVE A SOLUTION SLIGHTLY FASTER THAN THE 00Z ECMWF IS PREFERRED  
HERE. CONSIDERING THE MODEL SPREAD AND POSSIBLE SYSTEM  
ACCELERATION, CONFIDENCE IS BELOW AVERAGE HERE.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ROTH  

 
 
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