680  
FXUS10 KWNH 141836  
PMDHMD  
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
236 PM EDT SAT SEP 14 2019  
 
VALID SEP 14/1200 UTC THRU SEP 18/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..GREAT LAKES INTO NORTHEAST CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
A VERY FLAT BUT TIGHTLY PACKED HEIGHT PATTERN EXISTS ACROSS THE  
CONUS, PARTICULARLY THE NORTHERN CONUS AT THE START OF THE  
FORECAST PERIOD, WITH A SUBTLE SHORTWAVE CROSSING ND INTO MN  
TODAY. THIS WAVE WILL CROSS THE GREAT LAKES AND HELP TO BUILD  
SOME BROAD TROUGHING ACROSS THE NORTHEAST. THE 00Z ECMWF IS A BIT  
DEEPER THAN OTHER GUIDANCE BUT WITH LITTLE SIGNIFICANCE  
WEATHER-WISE TO SUPPORT THE GENERAL MODEL BLEND AT ABOVE AVERAGE  
CONFIDENCE.  
 
...DEEP LATITUDE TROF ENTERING THE WEST BY MONDAY; SOUTHWEST  
SHORTWAVE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 1/3RDS 12Z GFS & 2/3RDS 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
19Z UPDATE: THE 12Z UKMET SLOWED SIGNIFICANTLY BUT STILL REMAINS  
SLIGHTLY FASTER THAN THE REMAINING GUIDANCE, AND WITH LITTLE  
CHANGE IN THE ECMWF/CMC WILL KEEP INITIAL PREFERENCE OF GFS/ECMWF  
AT AVERAGE CONFIDENCE.  
 
---PRIOR DISCUSSION---  
GOES-WV SUITE DENOTES A NICE OUTFLOW TO THE SHORTWAVE ACROSS THE  
DESERT SOUTHWEST, THIS WILL MOVE NORTHWARD WITH SIMILAR EVOLUTION  
IN THE GUIDANCE SUITE. HOWEVER, TIMING IS GOING TO BE AN ISSUE  
BUT THIS IS MOSTLY AFFECTED BY THE TIMING OF THE UPSTREAM DIGGING  
LARGE SCALE TROF ENTERING N CA MONDAY. THERE HAS BEEN SOME  
GROWING CONSENSUS WITH THE UKMET/GFS SLOWING THROUGH MONDAY, BUT  
TYPICAL OF BIAS, BY TUESDAY THE SPLIT IN TIMING INCREASES. THE  
UKMET IS WELL OUTPACED OVER THE NAM/GFS FOLLOWED BY THE LAGGING  
ECMWF/CMC. THIS APPEARS TO BE A TRADITIONAL TIMING ISSUE, SO A  
TYPICAL GFS/ECMWF BLEND WILL LIKELY WORK BEST WITH AVERAGE  
CONFIDENCE (GIVEN SPREAD IS MODERATE TO LARGE BY DAY 3). SO  
EMPLOYING A 1/3RD GFS AND 2/3RDS ECWMF SOLUTION WORKS OUT WELL  
HERE.  
 
   
..GULF OF MEXICO TUTT AND SURFACE WAVE
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/CMC/ECWMF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
19Z UPDATE: THE 12Z UKMET TRENDED AWAY FROM THE STRONGER SOLUTION  
AND HAS BECOME CLOSER TO THE OTHER GUIDANCE, BUT IS A BIT FURTHER  
NORTH AND FASTER TO KEEP INCLUDED. THE 12Z CMC TRENDED FASTER AND  
MATCHES TIGHTLY WITH THE 12Z NAM/ECMWF TO SUGGEST THE GFS IS NOW A  
BIT TOO FAST AS WELL, SO WILL FAVOR A 12Z NAM/ECMWF/CMC BLEND.  
 
---PRIOR DISCUSSION---  
THE TUTT CELL MOVING WEST ACROSS THE GULF CONTINUES TO LOOK  
IMPRESSIVE WITH A SOLID TRAILING SURFACE WAVE. THE 12Z NAM AND  
ECMWF ARE VERY SIMILAR IN DEPTH AND TIMING OF BOTH FEATURES, WHILE  
THE GFS IS IN A SEMI-BIASED WEAKER PHASE RELATIVE TO BOTH BUT  
TIMED WELL. THE 00Z UKMET IS TYPICAL BIAS IN TROPICAL SYSTEMS  
WITH STRONG CONVECTIVE RESPONSE LEADING TO A COMPACT WAVE THAT  
FEEDS BACK ON ITSELF...SLOWING AND SHIFTING NORTH OF THE REMAINING  
GUIDANCE. THE 00Z CMC EVOLVES THE SURFACE WAVE WELL, BUT THE TUTT  
IS A BIT TOO WEAK AND SLOW, SO THE SURFACE WAVE LAGS. SO WHILE  
NOT FAVORED IN A BLEND, IT DOES PROVIDE CONFIDENCE TO THE  
EVOLUTION OF THE SYSTEM. SO A 12Z NAM/GFS AND 00Z ECMWF BLEND IS  
PREFERRED IN THE GULF AT SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
   
..TROPICAL STORM HUMBERTO
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: OFFICIAL NHC FORECAST  
BEST PROXY: 12Z CMC/ECMWF THROUGH 48HRS; 12Z GFS/NAM THEREAFTER  
CONFIDENCE: AVERAGE  
 
19Z UPDATE: THE 12Z ECMWF/CMC TRACK QUITE CLOSE TO THE 15Z NHC  
FORECAST THROUGH 48HRS, THEREAFTER THE CMC AND ECMWF SLOW  
SIGNIFICANTLY WITH THE NAM/GFS PASSING IT ALONG THE NHC TRACK.  
THE UKMET IS THE ONLY GUIDANCE MEMBER FASTER THAN NHC FORECAST  
TRACK BUT REMAINS VERY STRONG COMPARATIVELY AS WELL. SO THE BEST  
PROXY WILL BE THE CMC/ECWMF THROUGH 48HRS AND MORE GFS/NAM  
THEREAFTER.  
 
---PRIOR DISCUSSION---  
HUMBERTO IS STARTING TO HAVE A STRONGER/DEEPER APPEARANCE AT THIS  
TIME. THERE REMAINS A SOLID SPLIT IN THE GUIDANCE WITH THE  
ECMWF/UKMET CONTINUING TO BE EAST AND EVENTUALLY SOUTH OF THE NHC  
TRACK AFTER THE TURN AT 36 TO 48HRS. THE 12Z GFS/NAM BOTH START  
INITIALLY SLOWER AND SLIGHTLY EAST OF THE 00Z GUIDANCE BUT STILL  
ARE WEST AND NORTHWEST OVER THE NEXT TWO DAYS BEFORE TURNING EAST.  
THE 00Z CMC IS CLOSEST TO THE TRACK THROUGH 48HRS BEFORE  
ACCELERATING AFTER THE EASTWARD TURN...MOVING AWAY FROM THE OTHER  
GUIDANCE. IT IS AT THIS POINT THE GFS/NAM BOTH MOVE ALONG THE  
EASTWARD TRACK AFTER 48HRS WITH BETTER TIMING, PERHAPS A BIT SLOW.  
OVERALL, THE BEST PROXY IN A GENERAL MODEL BLEND, BUT TO NOT  
BLEND OUT THE FEATURES TOO MUCH; A 00Z CMC THROUGH 48HRS SHIFTING  
TO GFS/NAM THEREAFTER WORKS CLOSEST TO THE NHC FORECAST. THERE IS  
GROWING CONSENSUS AS THE GUIDANCE ENVELOPE TIGHTENS, AS SUCH  
CONFIDENCE IS AVERAGE IN UTILIZING THIS PROXY FOR THE 15Z NHC  
FORECAST.  
 
MODEL TRENDS AT WWW.WPC.NOAA.GOV/HTML/MODEL2.HTML  
500 MB FORECASTS AT WWW.WPC.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
GALLINA  
 

 
 
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