271   
FXUS10 KWNH 050721  
PMDHMD  
  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
321 AM EDT THU SEP 05 2019  
  
VALID SEP 05/0000 UTC THRU SEP 08/1200 UTC  
  
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
  
00Z FINAL MODEL EVALUATION, CONFIDENCE, AND PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GEFS/ECMWF  
CONFIDENCE: AVERAGE THROUGH 60 HOURS, BELOW AVERAGE FOR DAY 3  
  
07Z UPDATE: THE BIGGEST CHALLENGE REMAINS THE CONSIDERABLE SPREAD  
IN THE EVOLUTION, BOTH IN TIMING AND AMPLITUDE, OF A TROUGH  
DIGGING INTO THE WEST ON DAY 3. THE 00Z NON-NCEP SUITE DID LITTLE  
TO SQUELCH THE UNCERTAINTY, ALTHOUGH THE CMC AND UKMET REMAIN  
STRONG OUTLIERS. WILL MAINTAIN THE PREVIOUS PREFERENCES AND JUST  
UPDATE TO THE NEWEST GUIDANCE, AS THERE AT LEAST IS RUN TO RUN  
CONSISTENCY IN THESE MODELS.  
  
PREVIOUS DISCUSSION:  
WHILE THE GUIDANCE SHOWS CONSIDERABLE AGREEMENT IN THE SYNOPTIC  
EVOLUTION THROUGH THE FIRST 60 HOURS, IT DIVERGES CONSIDERABLY  
THEREAFTER, MOST NOTABLY IN THE WEST.  
  
THROUGH 60 HOURS, A LARGE RIDGE WILL PERSIST ACROSS THE MOUNTAIN  
WEST, WITH A TROUGH CONTINUING IN THE EAST. A SHORTWAVE DROPPING  
SE INTO THE GREAT LAKES THURSDAY NIGHT INTO FRIDAY WILL EVENTUALLY  
BE THE KICKER TO LIFT HURRICANE DORIAN QUICKLY AWAY FROM THE  
EASTERN SEABOARD. THE GUIDANCE IS IN VERY GOOD AGREEMENT IN TIMING  
AND AMPLITUDE OF THIS SHORTWAVE, WITH THE ONLY EXCEPTION BEING A  
SUBTLY DEEPER/FASTER IMPULSE NOTED BY THE 00Z GFS. THIS REMAINS  
WITHIN THE ENSEMBLE ENVELOPE AND HAS MINIMAL SPREAD OVERALL, SO A  
GENERAL MODEL BLEND CAN BE USED FOR THIS FEATURE.  
  
TWO ADDITIONAL SHORTWAVES WILL THEN TRAVERSE FROM THE PACNW ATOP  
THE MOUNTAIN WEST RIDGE AND INTO THE NORTHERN PLAINS. THE FIRST OF  
THESE DEAMPLIFIES QUICKLY AND SHOWS LITTLE AMPLITUDE BY THE TIME  
IT REACHES THE PLAIN. A MUCH MORE SIGNIFICANT FEATURE FOLLOWS  
BEHIND IT AS A MID-LEVEL LOW IN THE GULF OF ALASKA DROPS SOUTHWARD  
AND OPENS INTO A LONGWAVE TROUGH ALONG THE PACIFIC COAST. THIS IS  
WHERE GUIDANCE BEGINS TO SPLIT SIGNIFICANTLY. THE UKMET IS  
EXCEPTIONALLY FAST WEAKENING THIS FEATURE AND LIFTING IT EASTWARD  
INTO THE PLAINS, SO MUCH SO THAT BY DAY 3 IT IS 180 DEGREES OUT OF  
PHASE WITH THE GLOBAL CONSENSUS. THE CMC IS ALSO QUITE FAST, NOT  
AS MUCH AS THE UKMET, BUT AT THE VERY EDGE OF THE ENSEMBLE  
ENVELOPE. THE GFS/ECMWF ARE IN BETTER AGREEMENT, AND COMPARABLE TO  
THEIR MEANS, BUT STILL FEATURE DIFFERENT AMPLITUDES AND  
WAVELENGTHS OF THIS TROUGH AS IT OPENS TO THE EAST. THE MOST  
CLUSTERED GUIDANCE APPEARS TO BE A BLEND OF THE GEFS MEAN AND THE  
ECMWF, BUT CONFIDENCE IS BELOW AVERAGE. HOWEVER, WITH THE  
AGREEMENT OF THESE TWO INTO DAY 3, AND MINIMAL SPREAD PRIOR TO 60  
HOURS, A GEFS/ECMWF IS SUGGESTED FOR CONSISTENCY ACROSS THE CONUS  
FOR ALL 3 DAYS.  
  
   
..HURRICANE DORIAN  
  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PLEASE REFER TO THE OFFICIAL NATIONAL HURRICANE CENTER FORECAST  
TRACK  
  
WITH RESPECT TO THE 03Z NHC ADVISORY TRACK, A GLOBAL CONSENSUS IS  
SUFFICIENT THROUGH ABOUT 36 HOURS. THEREAFTER, MOST OF THE  
GUIDANCE IS A BIT SOUTH OF THE NHC TRACK, ALTHOUGH THE 00Z  
NON-NCEP SUITE DID SPEED UP A BIT FROM THE 12Z, AND IS BETTER  
MATCHED NOW TO THE NHC FORECAST POINTS. WHILE A GENERAL BLEND IS  
SUFFICIENT TO PRODUCE A BEST PROXY TO THE TRACK, FOR CONSISTENCY A  
GEFS/ECMWF/UKMET IS STILL PREFERRED FOR THE BEST TRACK COMPARED TO  
THE 03Z ADVISORY POSITIONS.  
   
  
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
  
WEISS  
  
  
 
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