423  
FXUS10 KWNH 271712  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1211 PM EST TUE FEB 27 2018  
 
VALID FEB 27/1200 UTC THRU MAR 03/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...NORTHERN STREAM SHORTWAVE CROSSING THE NORTHERN PLAINS THROUGH  
WEDNESDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THROUGH MUCH OF WEDNESDAY NIGHT, THE MODELS HAVE CONVERGED TO A  
COMMON SOLUTION COMPARED TO YESTERDAY, WITH THE NON-NCEP GUIDANCE  
MOVING TOWARD THE NAM/GFS. BEYOND ABOUT 12Z THURSDAY, THERE ARE  
DIFFERENCES WITH THE INTERACTION OF THIS WAVE AND A SOUTHERN  
STREAM FEATURE; DISCUSSED BELOW.  
 
   
..CLOSED LOW OVER THE CALIFORNIA COAST TODAY
 
BECOMING AN OPEN  
WAVE AS IT TRACKS INTO THE SOUTHERN PLAINS LATE WEDNESDAY...   
..RESULTANT SURFACE CYCLONE INTO THE OHIO VALLEY ON THURSDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND THROUGH 00Z/02  
00Z UKMET/ECMWF MEAN/06Z GEFS MEAN BLEND 00Z/02-03  
CONFIDENCE: BELOW AVERAGE  
 
WHILE SOME MINOR SPREAD REMAINS IN THE ENSEMBLE SPAGHETTI PLOTS,  
THERE HAS BEEN DECENT RUN TO RUN CONSISTENCY FROM THE PAST 3  
CYCLES. THE 00Z ECMWF IS TOWARD THE SLOWER SIDE WITH THE 00Z ECMWF  
MEAN A BIT AHEAD OF THE DETERMINISTIC ECMWF. THE 12Z NAM IS  
NOTICEABLY FASTER WHILE THE 00Z UKMET/CMC AND 12Z GFS ARE NEAR THE  
MIDDLE THROUGH ABOUT 00Z/01.  
 
BEYOND 00Z/01 (WEDNESDAY EVENING), THE ECMWF/UKMET/CMC HAVE  
TRENDED AWAY FROM A MORE AMPLIFIED NORTHERN STREAM WAVE WHICH 12Z  
NAM SHOWS AS RATHER DEEP OVER THE OHIO VALLEY THURSDAY NIGHT AS IT  
PHASES/INTERACTS WITH ENERGY STREAKING ACROSS THE MIDDLE  
MISSISSIPPI VALLEY. THE 12Z GFS LOOKS REASONABLE UNTIL LATE IN THE  
DAY ON THURSDAY WHEN IT TRENDS TOWARD THE STRONGER SIDE OF THE  
MODEL SPREAD CONSIDERING GEFS SCATTER LOW PLOT STRENGTHS. THE GFS  
APPEARS TOO STRONG/NORTH WITH ITS LOW PLACEMENT IN NEW ENGLAND BY  
12Z/02 AS IT IS ON THE STRONGER SIDE OF THE ENSEMBLE GUIDANCE BUT  
NONE OF THE MODELS ARE OUTLIERS. THE 00Z ECMWF LOOKS SLOWER THAN  
IDEAL WITH THE PASSAGE OF THE NORTHERN STREAM WAVE WHICH IMPACTS  
PHASING AND STRENGTH OF THE STORM SYSTEM DOWNSTREAM NEAR NEW  
ENGLAND.  
 
UNFORTUNATELY, NO SINGLE DETERMINISTIC MODEL APPEARS IDEAL HERE AS  
THEY ALL SEEM TO HAVE ISSUES IN THE WAY THEY EVOLVE, BUT THE 00Z  
UKMET MAY BE THE BEST OF THE DETERMINISTIC GUIDANCE, ESPECIALLY BY  
FRIDAY MORNING NEAR THE NORTHEAST WITH THE ENSEMBLE TRENDS IN THE  
SCATTER LOW PLOTS LEAVING LOTS OF ROOM FOR CHANGES. THE 00Z UKMET  
BLENDED WITH THE 06Z GEFS MEAN AND 00Z ECMWF MEAN SEEMS BEST AT  
THIS TIME, WITH THE GEFS STRONGER AND ECMWF WEAKER.  
 
...LARGE CLOSED LOW OFF OF THE PACIFIC NORTHWEST BY THURSDAY  
EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS ALL SHOW SIMILARLY HERE, ENOUGH FOR A GENERAL MODEL  
BLEND WITH DECENT ENSEMBLE AGREEMENT.  
 
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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