402  
FXUS10 KWNH 261838  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
137 PM EST MON FEB 26 2018  
 
VALID FEB 26/1200 UTC THRU MAR 02/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...DEPARTING WEAK POSITIVELY TILTED SHORTWAVE EXITING THE EASTERN  
U.S. TODAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
...NORTHERN STREAM SHORTWAVE CROSSING THE NORTHERN PLAINS THROUGH  
WEDNESDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
BOTH THE 12Z NAM/GFS ARE QUICKER WITH THIS SHORTWAVE COMPARED TO  
THE 00Z ECMWF/UKMET/CMC, BUT THE 12Z GFS BECOMES ONE OF THE  
FASTEST COMPARED TO THE ENSEMBLE SPREAD WEDNESDAY NIGHT AND  
BEYOND. ENSEMBLE MEANS SUPPORT A BLEND CLOSER TO A 12Z NAM/00Z  
ECMWF BLEND WITH THE 12Z NAM SLIGHTLY QUICKER AND 00Z ECMWF SLOWER  
THAN THE MEANS.  
 
   
..CLOSED LOW FORMING OVER THE CALIFORNIA COAST TONIGHT
 
BECOMING  
AN OPEN WAVE AS IT TRACKS INTO THE SOUTHERN PLAINS LATE  
WEDNESDAY...   
..RESULTANT SURFACE CYCLONE INTO THE OHIO VALLEY ON THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/UKMET BLEND  
CONFIDENCE: AVERAGE  
 
SIMILAR TO THE ABOVE REFERENCED SYSTEM, THE 12Z GFS BECOMES FASTER  
THAN THE REMAINING MODEL CONSENSUS WITH THIS FEATURE, AND WHILE  
NOT AN OUTLIER WITH RESPECT TO THE SPAGHETTI ENSEMBLE DISTRIBUTION  
OF 500 MB HEIGHT CONTOURS, THE 12Z GFS HAS LITTLE DETERMINISTIC  
SUPPORT. THERE IS SOME POSSIBLE INTERACTION WITH THE NORTHERN  
STREAM SHORTWAVE REFERENCED ABOVE WITH THE SOUTHERN STREAM WAVE  
REFERENCED HERE, BUT THE RESULTING SURFACE CYCLONE SHOWS  
REASONABLY WELL IN THE PAST FEW ENSEMBLE CYCLES REGARDING THE  
SURFACE LOW BY 12Z/01 IN THE OHIO VALLEY. WHILE SCATTER LOW PLOTS  
FROM THE 00Z/26 ENSEMBLES SUPPORT A SOLUTION CLOSER TO THE 00Z  
ECMWF, THE FASTER 12Z NAM/GFS COULD BE ON TO A TREND SO A BLEND OF  
THE SOMEWHAT QUICKER 12Z NAM AND 00Z ECMWF IS PREFERRED FOR THIS  
SYSTEM. IN FACT, THE 12Z ECMWF/UKMET BOTH SHIFTED EAST A BIT, BUT  
NOT TO THE DEGREE OF THE 12Z GFS.  
 
WORTH NOTING, THE 12Z NAM 500 MB LOW APPEARS TOO WEAK FROM 12Z/01  
- 00Z/02 WHICH MAY RESULT IN THE SURFACE LOW FROM THE 12Z NAM  
BEING TOO WEAK. THE 12Z ECMWF/UKMET APPEAR MORE REASONABLE HERE,  
WITH THE ECMWF A BIT SLOWER/STRONGER ALOFT, AND THE 12Z UKMET A  
BIT WEAKER/FASTER ALOFT.  
 
...LARGE CLOSED LOW OFF OF THE PACIFIC NORTHWEST BY THURSDAY  
EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 2/3 12Z ECMWF, 1/3 12Z GFS BLEND  
CONFIDENCE: AVERAGE  
 
ENSEMBLES HAVE SHOWN THE GEFS/GFS MODELS TO BE CONSISTENTLY  
QUICKER WITH THE EVOLUTION OF THE CLOSED LOW OFF OF THE PACIFIC  
NORTHWEST BY THURSDAY EVENING. THE 12Z NAM IS ALSO QUICKER. GIVEN  
THE CONSISTENT SIGNAL NOTED IN THE ENSEMBLES, A BLEND WEIGHTED  
TOWARD THE MIDDLE IS PREFERRED. THE MIDDLE IS BEST REPRESENTED BY  
A 12Z GFS/12Z ECMWF BLEND, BUT WITH MORE WEIGHT TOWARD THE ECMWF.  
ONLY MINOR CHANGES WERE NOTED IN THE 12Z ECMWF/UKMET/CMC COMPARED  
TO THEIR 00Z CYCLES REGARDING THIS SYSTEM.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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