841  
FXUS10 KWNH 271938  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
237 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 MODEL EVALUATION ALONG WITH FINAL 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: NON-12Z NAM BLEND THROUGH 00Z/02  
12Z ECMWF/UKMET/CMC 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 REGARDING THE SOUTHERN STREAM SHORTWAVE AS IT REACHES THE  
SOUTHERN PLAINS WEDNESDAY NIGHT. THE 12Z ECMWF SPED UP SLIGHTLY  
COMPARED TO THE SLOWER 00Z ECMWF...WITH THE 00Z ECMWF AND 12Z  
UKMET TOWARD THE SLOWER SIDE OF THE MODELS AND THE 00Z ECMWF MEAN  
A BIT AHEAD OF BOTH THE 00Z AND 12Z DETERMINISTIC ECMWF. THE 12Z  
NAM WAS NOTICEABLY FASTER WHILE THE 12Z GFS WAS NEAR THE MIDDLE  
THROUGH ABOUT 00Z/01.  
 
BEYOND 00Z/01 (WEDNESDAY EVENING), THE 00Z 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 ECMWF?UKMET/CMC STAYED THE COURSE  
WHICH MAKES THE 12Z NAM SEEM UNLIKELY IN THE WAY IT EVOLVES ACROSS  
THE UPPER MIDWEST/OHIO 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 ENSEMBLE SPAGHETTI ENSEMBLE  
PLOTS. 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 DETERMINISTIC MODELS ARE  
OUTLIERS.  
 
UNFORTUNATELY, NO SINGLE DETERMINISTIC MODEL APPEARS IDEAL HERE AS  
THEY ALL SEEM TO HAVE ISSUES IN THE WAY THEY EVOLVE. HOWEVER, THE  
12Z ECMWF/UKMET/CMC TRENDED IN THE DIRECTION OF THE 12Z NAM/GFS  
BUT NOT TO THEIR EXTREMES. WHILE DIFFERENCES REMAIN AMONG THE 12Z  
ECMWF/UKMET/CMC...A BLEND OF THESE THREE MODELS APPEARS BEST AT  
THIS TIME, ESPECIALLY BY FRIDAY MORNING NEAR THE NORTHEAST WITH  
THE ENSEMBLE TRENDS IN THE SCATTER LOW PLOTS LEAVING LOTS OF ROOM  
FOR CHANGES.  
 
...LARGE CLOSED LOW OFF OF THE PACIFIC NORTHWEST BY THURSDAY  
EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
DESPITE SOME TIMING/STRENGTH DIFFERENCES, THE MODELS ALL SHOW  
SIMILARLY WITH THE LARGE CLOSED LOW ALONG THE WEST COAST, 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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page