472  
FXUS10 KWNH 221732  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
131 PM EDT SUN OCT 22 2017  
 
VALID OCT 22/1200 UTC THRU OCT 26/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION...WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...UPPER TROUGH CROSSING THE NRN PLAINS/UPPER MS VALLEY TODAY WITH  
ATTENDANT COLD FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
ONLY MINOR TIMING DIFFERENCES SHOW UP WITH THE LATEST MODELS  
REGARDING THE COLD FRONT ACROSS THE GREAT LAKES REGION...BUT THEY  
ARE SMALL ENOUGH TO PREFER A GENERAL MODEL COMPROMISE.  
 
   
..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/OH VALLEYS
 
   
..DEEP PHASED CYCLONE OVER THE GREAT LAKES REGION B-Y TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 40% 00Z ECMWF...40% 12Z NAM...20% 12Z GFS BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
AN DEVELOPING CLOSED LOW APPROACHING THE LOWER MS VALLEY THIS  
AFTERNOON IS EXPECTED TO ADVANCE EAST-NORTHEASTWARD OVER THE NEXT  
24-36 HOURS WHILE ELONGATING AND ACQUIRING A NEGATIVE TILT. LOWER  
THERE CONTINUES TO BE TIMING DIFFERENCES WITH THE SHORTWAVE AS IT  
SWINGS NORTHEASTWARD AHEAD OF AN UPSTREAM AMPLIFYING UPPER TROUGH.  
THE GFS HAS BEEN RATHER INCONSISTENT FROM RUN TO RUN AND IS  
CURRENTLY TOWARD THE FASTER SIDE OF THE DETERMINISTIC GUIDANCE.  
WHILE OTHER MODELS AND ENSEMBLE GUIDANCE HAS SHOWN SLIGHTLY  
QUICKER TRENDS SINCE YESTERDAY...IT IS THOUGHT THE 12Z GFS IS TOO  
FAST. THE ECMWF HAS ONLY SHOWN MINOR CHANGES OVER THE PAST 3  
CYCLES ENDING WITH ITS 00Z/22 CYCLE.  
 
A TIMING CLOSER TO THE 00Z ECWMF/12Z NAM...WITH A SLIGHT NUDGE IN  
THE DIRECTION OF THE 12Z GFS IS RECOMMENDED. THIS BLEND STAYS  
TOWARD THE MIDDLE TO FRONT EDGE OF THE LATEST ENSEMBLE  
GUIDANCE...AND IS FASTER THAN THE 00Z UKMET/CMC...WITH THE 00Z CMC  
CONSIDERED LEAST LIKELY TO VERIFY GIVEN OVERALL MODEL TRENDS AND  
ITS PLACEMENT TOWARD THE SLOWER END OF THE ENSEMBLE GUIDANCE.  
CONFIDENCE REMAINS A BIT LOWER THAN AVERAGE GIVEN THE POOR RUN TO  
RUN CONSISTENCY IN A MAJORITY OF THE MODEL GUIDANCE.  
 
...SHORTWAVE CROSSING B.C./PACIFIC NORTHWEST TODAY AND SWEEPING  
ACROSS THE NORTHERN PLAINS/MIDWEST MON...   
..WEST COAST RIDGE/SANTA ANA WIND DEVELOPMENT MON/TUES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
ALTHOUGH THE 00Z CMC REMAINS A BIT STRONGER WITH THE LOW-MID LEVEL  
RIDGE OVER THE WESTERN U.S...THERE IS ENOUGH AGREEMENT TO SUPPORT  
A GENERAL MODEL COMPROMISE.  
 
   
..SHORTWAVE DIGGING TOWARD THE NORTHERN PLAINS TUES NIGHT
 
   
..ASSOCIATED SURFACE LOW OVER SOUTHERN CANADA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 00Z UKMET/00Z ECMWF/12Z GFS  
CONFIDENCE: AVERAGE  
 
THE 00Z UKMET SPLITS THE DIFFERENCE IN POSITION AND IS A BIT  
WEAKER THAN THE FASTER/SOUTHERN 00Z ECMWF AND SLOWER/NORTHERN 12Z  
GFS. A 3-WAY BLEND OF THE 00Z UKMET/00Z ECMWF/12Z GFS FITS TOWARD  
THE MIDDLE OF THE LATEST ENSEMBLE SPREAD WITH NO CONSISTENT TRENDS  
NOTED IN THE LATEST GUIDANCE.  
 
   
..SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST BY WED
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/00Z UKMET/00Z ECMWF MEAN  
CONFIDENCE: AVERAGE  
 
THE 00Z ECMWF HAS BEEN CONSISTENTLY TOWARD THE DEEPER SIDE OF THE  
DETERMINISTIC/ENSEMBLE SPREAD WITH THE ECMWF MEAN CONSISTENTLY  
WEAKER/FLATTER WITH THE SHORTWAVE AS IT REACHES THE NORTHWEST  
U.S./SOUTHWEST CANADA. THE 12Z GFS/00Z UKMET IS SLIGHTLY WEAKER  
THAN THE 00Z ECMWF MEAN BUT A BLEND OF THE 3 MODELS SHOULD ALLOW  
FOR A FAVORABLE COMPROMISE/BLEND REGARDING THIS =SYSTEM TO AFFECT  
THE INTERIOR NORTHWEST.  
 
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