707  
FXUS10 KWNH 211646  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1246 PM EDT SAT OCT 21 2017  
 
VALID OCT 21/1200 UTC THRU OCT 25/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...LONGWAVE TROUGH OVER THE WESTERN U.S. EJECTING INTO THE PLAINS  
TODAY ALONG WITH ASSOCIATED COLD FRONT...   
..SURFACE LOW DEEPENING OVER SOUTHERN CANADA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
   
..SOUTHERN STREAM LOWER MS VALLEY CLOSED LOW DEVELOPMENT BY MON
 
   
..SURFACE COLD FRONT SWEEPING ACROSS THE MS/TN VALLEYS
 
   
..SURFACE LOW DEVELOPMENT OVER THE TN VALLEY
 
   
..DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION BY TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS HAVE BEGIN TO MORE CONSISTENTLY TREND FASTER WITH AN  
UPSTREAM MID-UPPER LEVEL TROUGH AMPLIFYING INTO THE N-CNTRL U.S.  
ON MONDAY WHICH IS HELPING TO EJECT THE FORECAST CLOSED LOW OVER  
THE MISSISSIPPI VALLEY QUICKER TO THE EAST. TRENDS IN THE  
ENSEMBLES WERE FLIP FLOPPING BETWEEN FASTER AND SLOWER THROUGH  
FRIDAY BUT THAT FLIP FLOPPING APPEARS TO HAVE ENDED.  
 
CURRENTLY...THE 12Z NAM/GFS ARE THE FASTEST TO LIFT THE SRN STREAM  
CLOSED LOW ACROSS THE ERN U.S. ON MONDAY WHILE THE 00Z UKMET/CMC  
LAG BEHIND. THE 00Z ECMWF SPLITS THE DIFFERENCE BETWEEN THE FASTER  
NCEP MODELS AND THE SLOWER NON-NCEP MODELS BUT LEAN CLOSER TO THE  
12Z NCEP IDEA. THE LATEST ENSEMBLE SPREAD REMAINS FAIRLY LARGE BUT  
THE TREND TOWARD FASTER IS ALSO SEEN IN THE ENSEMBLE GUIDANCE OVER  
THE PAST 3 CYCLES. GIVEN THE FLIP FLOPPING IN TRENDS APPEARS TO  
HAVE ENDED ...WILL GO TOWARD THESE FASTER MODELS WHICH IS A CHANGE  
FROM CONTINUITY...BUT NOT GOING ALL THE WAY TOWARD THE FASTEST  
MODELS...I.E. THE 12Z NAM AND 12Z GFS.  
 
   
..SHORTWAVE REACHING B.C./PAC NORTHWEST TONIGHT
 
   
..ATMOSPHERIC RIVER OVER THE PACIFIC NORTHWEST THIS WEEKEND
 
   
..UPPER TROUGH SWEEPING ACROSS THE NORTHERN PLAINS/MIDWEST MON
 
   
..WEST COAST RIDGE/SANTA ANA WIND DEVELOPMENT MON/TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL CONSENSUS THROUGH 00Z/24  
CONFIDENCE: ABOVE AVERAGE  
 
GENERALLY GOOD AGREEMENT EXISTS WITH THE TROUGH CURRENTLY  
APPROACHING THE PACIFIC NORTHWEST. THE LATEST DETERMINISTIC AND  
ENSEMBLE GUIDANCE SHOWS GOOD AGREEMENT WITH THE EVOLUTION OF THE  
UPPER TROUGH INTO THE PLAINS THROUGH SUNDAY NIGHT AND UPPER LEVEL  
RIDGING BUILDING OUT OVER THE WEST COAST. WHILE THE 00Z CMC IS A  
BIT STRONGER AND 00Z ECMWF A BIT WEAKER WITH LOW-MID LEVEL RIDGE  
OVER CALIFORNIA/NEVADA BY TUESDAY EVENING...THE CMC AND ECMWF HAVE  
THE SAME GENERAL IDEA AS THE REMAINING MODELS WITH PLACEMENT FROM  
THE LOWER TO UPPER LEVELS WITH A STRONG RIDGE.  
 
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WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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