373  
FXUS10 KWNH 221839  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
238 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 MODEL EVALUATION...WITH FINAL 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: 12Z ECMWF/NAM/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
A 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. 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 12Z ECMWF/NAM/UKMET IS RECOMMENDED...WHICH  
IS A LITTLE FASTER THAN THE OVERNIGHT PREFERENCE. THIS BLEND STAYS  
TOWARD THE MIDDLE TO FRONT EDGE OF THE LATEST 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 12Z 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 12Z GFS/12Z ECMWF  
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. THE 12Z UKMET/ECMWF ADJUSTED NORTH...BUT THE 12Z UKMET IS NOW  
CONSIDERED TOO FAR NORTH TO BE INCLUDED IN THE BLEND. A SIMPLE  
BLEND OF THE 12Z GFS/ECMWF 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: NON 12Z NAM BLEND  
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 ECMWF ADJUSTED FLATTER AND WHEN  
COMBINED WITH THE 12Z GFS/UKMET/CMC...A FAVORABLE COMPROMISE/BLEND  
IS REACHED. THE 12Z NAM IS TOWARD THE FASTER END OF THE LATEST  
GUIDANCE AND IS NOT INCLUDED IN THE PREFERENCE.  
 
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