125  
FXUS10 KWNH 011844  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
243 PM EDT WED NOV 1 2017  
 
VALID NOV 1/1200 UTC THRU NOV 5/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z FINAL MODEL EVALUATION WITH PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
SHORTWAVE AND SURFACE LOW CROSSING NORTHERN TIER OF THE U.S.  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS ARE VERY CLOSE IN THEIR MASS FIELDS FOR THIS LOW AMPLITUDE  
WAVE AS IT EJECTS EAST-NORTHEAST THROUGH THE NORTH-CENTRAL US AND  
SOUTHEAST CANADA. THE MODELS ALSO SHOW GOOD AGREEMENT ON THE  
TIMING AND PLACEMENT OF THE WAVE ITSELF AND THE ASSOCIATED SURFACE  
LOW AND COLD FRONT. THEREFORE...A GENERAL MODEL BLEND IS  
RECOMMENDED WITH HIGH CONFIDENCE.  
 
18Z UPDATE: THE 12Z ECMWF HAS TRENDED SLIGHTLY DEEPER AND A  
LITTLE MORE SUPPRESSED WITH THE SURFACE LOW TRACKING ACROSS THE  
NORTHERN GREAT LAKES BY THURSDAY NIGHT. HOWEVER, IT AGREES WELL  
WITH THE REMAINING GUIDANCE AND CAN BE INCORPORATED INTO THE  
FORECAST.  
 
PACIFIC NORTHWEST STORM SYSTEM ARRIVING ON FRIDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND AFTER 12Z FRIDAY  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A SHORTWAVE DIGGING SOUTH FROM NORTHWEST CANADA WILL AMPLIFY A  
TROUGH OVER THE PACIFIC NORTHWEST THURSDAY AND INTO FRIDAY...AND  
LIKELY PRODUCE A CLOSED LOW FOR A TIME. THE DIGGING SHORTWAVE  
SHOULD PRODUCE A SURFACE LOW OFF THE COAST OF VANCOUVER ISLAND OR  
WASHINGTON...AND MODELS ARE IN GOOD AGREEMENT OVERALL WITH THIS  
LARGE SCALE EVOLUTION. THE PRIMARY OUTLIER IS THE 00Z CMC WHICH  
APPEARS TO BE STRONGER WITH THE INITIAL WAVE DIGGING SOUTH...AND  
THIS EVENTUALLY LEADS TO A STRONGER LOW THAT CLOSES OFF A BIT  
FURTHER WEST. AS THE TROUGH BEGINS TO DEAMPLIFY...THE CMC IS ALSO  
SLOWER WITH THAT PROCESS...LAGGING THE TROUGH BEHIND THE OTHER  
GLOBAL MODELS. GIVEN THE LACK OF SUPPORT FROM ANY OTHER MODEL THE  
CMC HAS BEEN EXCLUDED FROM THE PREFERENCE AT THIS TIME.  
ADDITIONALLY...WITH A DEAMPLIFYING WAVE...EXPECTATIONS ARE THAT  
THE TROUGH AXIS WOULD SHIFT FASTER THAN WHAT THE CMC IS SHOWING.  
 
THE REMAINDER OF THE MODELS ARE FAIRLY CLOSE WITH THEIR MASS  
FIELDS...PARTICULARLY ABOVE 700MB. LOWER LEVELS ARE SOMEWHAT  
MESSIER...WHICH IS NOT UNCOMMON IN THE WEST...BUT THESE  
DIFFERENCES DO NOT SEEM TO HAVE A SIGNIFICANT DIFFERENCE IN  
SENSIBLE WEATHER IMPACTS. THE 12Z NAM IS COLDER WITH ITS  
TEMPERATURE PROFILES IN THE CORE OF THE TROUGH (WASHINGTON AND  
OREGON). THIS IS A USUAL BIAS WHICH MAY LEAD TO SLIGHTLY LOWER  
SNOW LEVELS IN THOSE AREAS...BUT THE DIFFERENCES ARE NOT  
SIGNIFICANT ENOUGH AT THIS TIME TO EXCLUDE IT FROM THE BLEND.  
 
18Z UPDATE: THE 12Z ECMWF MAINTAINS EXCELLENT CONTINUITY WITH ITS  
PREVIOUS RUN REGARDING THIS STORM SYSTEM. THE CMC BEGINS  
DIVERGING FROM THE MODEL CONSENSUS BY FRIDAY AFTERNOON, BUT CAN BE  
INCORPORATED BEFORE THAT TIME.  
 
SHORTWAVE TRACKING NEAR THE GULF COAST FRIDAY AND SATURDAY  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z ECMWF/12Z ECMWF/12Z GEFS MEAN BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
CONFIDENCE IS LOWER WITH THE EXACT PLACEMENT AND TIMING OF  
SHORTWAVES IN THE SOUTHERN TIER OF STATES OVER THE NEXT FEW DAYS.  
THE MOST DISTINCT SHORTWAVE IS EXPECTED TO EVOLVE FROM A RESIDUAL  
TROUGH OVER SOUTHERN CALIFORNIA...AND SHOULD DEAMPLIFY AND  
ACCELERATE THROUGH THE SOUTHWEST TOMORROW. THE 12Z NAM AND 12Z CMC  
EVENTUALLY TAKE THIS SHORTWAVE AND DIG IT INTO  
FLORIDA...AMPLIFYING A TROUGH IN THAT REGION. THE OTHER MODELS  
SHOW VARYING DEGREES OF GRADUAL HEIGHT FALLS...WITH THE 00Z ECMWF  
AND 12Z GEFS MEAN SHOWING A TROUGH BUT WITH A LOWER AMPLITUDE AND  
STRENGTH AS COMPARED TO THE NAM/CMC. THE 12Z GFS AND 00Z UKMET ARE  
LEAST AMPLIFIED AND GENERALLY SHOW A FLATTER HEIGHT FIELD THROUGH  
THE SOUTHEASTERN U.S. GIVEN THE SUBTROPICAL RIDGE IS WELL-FORECAST  
TO DRIFT WEST...THIS SHOULD OPEN UP AN AVENUE FOR TROUGH  
DEVELOPMENT IN THE VICINITY OF FLORIDA...BUT GIVEN THE WEAKNESS OF  
THE SHORTWAVE IT DOES NOT APPEAR LIKELY TO BE AS STRONG AS THE NAM  
AND CMC ARE DEPICTING. FOR THAT REASON...THE PREFERENCE IS FOR A  
BLEND OF THE ECMWF AND GEFS ENSEMBLE MEAN.  
 
18Z UPDATE: THE 12Z ECMWF TRENDED FASTER WITH THE WEAK LEAD  
SHORTWAVE CROSSING TEXAS ON THURSDAY, AND SLIGHTLY MORE AMPLIFIED  
WITH THE MAIN SHORTWAVE TROUGH TRACKING ACROSS THE DEEP SOUTH  
FRIDAY NIGHT INTO SATURDAY.  
 
WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS/HAMRICK  
 

 
 
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