687  
FXUS10 KWNH 271924  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
324 PM EDT TUE AUG 27 2019  
 
VALID AUG 27/1200 UTC THRU AUG 31/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z FINAL MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..OVERALL PATTERN ACROSS THE CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
TD 06L NHC PROXY: 12Z UKMET/ECMWF AND 00Z GEFS BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
19Z UPDATE:  
FOR TD6, UKMET REMAINS VERY CLOSE TO ITS PREVIOUS RUN, WHILE THE  
ECMWF HAS SLOWED ONCE AGAIN TO BECOME MORE IN LINE WITH THE  
PREVIOUS BLEND AND CLOSE TO THE NHC TRACK. FOR THIS REASON HAVE  
ADDED THE ECMWF TO THE PREFERRED BLEND FOR THIS UPDATE. ELSEWHERE,  
A GENERAL MODEL BLEND STILL REMAINS SUFFICIENT. THE GFS IS A BIT  
FAST WITH SWINGING A TROUGH AXIS/SHORTWAVE ACROSS NEW ENGLAND ON  
THURSDAY WITH MAY SPREAD QPF A BIT TOO FAST, BUT IS OTHERWISE WELL  
WITHIN THE ENSEMBLE ENVELOPE THROUGH THE PERIOD ACROSS THE  
REMAINDER OF THE CONUS.  
 
PREVIOUS DISCUSSION:  
FOR TD6 MOVING NORTHEAST OFF THE EASTERN COAST OF THE CONUS  
THROUGH THE PERIOD, THE NHC TRACK IS A BIT SLOWER THAN THE  
MAJORITY OF THE AVAILABLE GLOBAL SUITE. HOWEVER, A BLEND OF THE  
UKMET AND GEFS MEAN PRODUCES SOMETHING REASONABLY CLOSE TO THE  
TRACK AS THESE ARE ON THE SLOW EDGE OF THE ENVELOPE. THE TREND IN  
THE ECMWF HAS BEEN TOWARDS THIS SLOWER SOLUTION OVER THE PAST 3  
RUNS, SO SOME WEIGHT ON THE ECMWF IS USABLE, BUT WILL END UP WITH  
SOMETHING THAT GRADUALLY GETS MORE AWAY FROM THE OFFICIAL TRACK.  
FOR THIS REASON, A UKMET/GEFS BLEND IS SUGGESTED. THIS WILL ALSO  
PLAY A ROLE IN THE QPF, ESPECIALLY ACROSS EASTERN NEW ENGLAND  
THURSDAY AS INTERACTION WITH THE APPROACHING FRONT HAS THE  
POTENTIAL TO PRODUCE HEAVY RAINFALL. THE UKMET IS THE MOST  
AGGRESSIVE WITH QPF, AND DESPITE ITS TYPICAL WET BIAS, IT BEING  
THE BEST DETERMINISTIC MODEL TOWARDS THE TRACK SUGGESTS AN  
INCREASING LIKELIHOOD FOR HEAVY RAINFALL, SO FROM A QPF STANDPOINT  
A GENERAL MODEL BLEND IS ACCEPTABLE HERE.  
 
ELSEWHERE ACROSS THE CONUS, THERE IS GENERALLY GOOD AGREEMENT IN A  
WESTERN RIDGE/EASTERN TROUGH GENERALLY BECOMING MORE ZONAL BY DAY  
3. WHILE SUBTLE DIFFERENCES EXIST IN TIMING AND INTENSITY OF  
FEATURES WHICH WILL EVENTUALLY DESCRIBE THE SYNOPTIC SHIFT, THE  
SPREAD APPEARS MINIMAL. THE BIGGEST DISCREPANCIES LIE IN THE  
AMPLITUDE OF THE WESTERN RIDGE EARLY IN THE FORECAST PERIOD, BUT  
OVERALL THE QPF ALONG THE STALLED FRONT IN THE SOUTH AND HEIGHT  
ANOMALIES BY DAY 3 FEATURE A SMALL ENVELOPE, SO A GENERAL MODEL  
BLEND SHOULD BE SUFFICIENT.  
 
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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