917  
FXUS10 KWNH 281659  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1158 AM EST WED FEB 28 2018  
 
VALID FEB 28/1200 UTC THRU MAR 04/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
 
 
...SHORTWAVE OVER THE SOUTHWEST, EJECTING EASTWARD INTO THE PLAINS  
TONIGHT AND REACHING THE EAST COAST LATE THURSDAY WHILE  
INTERACTING WITH A NORTHERN STREAM WAVE DROPPING SOUTH FROM THE  
UPPER MISSISSIPPI VALLEY...  
...RESULTANT SURFACE CYCLONE INTO THE OHIO VALLEY ON THURSDAY WITH  
SURFACE LOW REFORMING SOUTHEAST OF THE NEW ENGLAND COAST THROUGH  
FRIDAY MORNING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 50% 12Z NAM, 25% 12Z GFS, 25% 00Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
00Z GEFS/ECMWF/CMC ENSEMBLE SPAGHETTI HEIGHTS AT 534 DAM CONTINUE  
TO SHOW THE GEFS AND OLDER RUNS OF THE GFS AS STRONGER AND ON THE  
WESTERN EDGE OF THE AVAILABLE MEMBERS VALID FRIDAY ACROSS THE  
NORTHEAST. ENSEMBLE TRENDS IN THE HEIGHTS AND SURFACE LOW PLOTS  
HAVE SHOWN A WESTERN SHIFT VALID 12Z/02 OFFSHORE OF NEW ENGLAND  
WITH THE GEFS MEMBERS ON THE FAR NORTHWESTERN EDGE AND ECMWF  
MEMBERS THE SOUTHEASTERN EDGE OF THE ENVELOPE OF SOLUTIONS. THE  
PREFERENCE IS TO BE NEAR THE CENTROID OF THE AVAILABLE ENSEMBLE  
SCATTER LOW PLOT POSITIONS, CONSIDERING TRENDS, WHICH IS BETWEEN  
THE 00Z GEFS AND 00Z EC MEMBERS, OR NEAR THE 12Z NAM POSITION  
VALID 12Z/02.  
 
THE 12Z GFS HAS COME INTO BETTER AGREEMENT WITH THIS PREFERENCE  
BUT CONTINUES TO LIE ON THE NORTHERN SIDE OF THE GUIDANCE, WHILE  
THE 00Z ECMWF IS ON THE SOUTH SIDE. VALID 00Z/03, THE 12Z NAM ENDS  
UP ON THE WESTERN SIDE OF THE ENSEMBLE SPREAD, AND DESPITE TRENDS  
IN THAT DIRECTION FROM THE ENSEMBLES, BLENDING WITH THE FARTHER  
EAST 12Z GFS AND 00Z ECMWF APPEARS PRUDENT. REGARDING MASS FIELDS,  
THE 12Z NAM LOOKS TO BE THE CLOSEST OF THE DETERMINISTIC MODELS TO  
THE PREFERENCE, WHILE THE 12Z GFS AND 00Z ECMWF ARE CONSIDERED  
SECONDARY PREFERENCES GIVEN THE 00Z UKMET/CMC APPEAR TOO BE  
DISPLACED IN STRENGTH AND/OR POSITION FROM THE PREFERENCE.  
 
DIFFERENCES WITH THE LOW LEVEL THERMAL FIELDS ACROSS THE NORTHERN  
MID-ATLANTIC AND NORTHEAST SHOW THE 12Z NAM COLDEST WITH 12Z GFS  
WARMEST AND 00Z ECMWF SOMEWHERE IN THE MIDDLE OF THE TWO.  
 
 
...LARGE CLOSED LOW OFF OF THE PACIFIC NORTHWEST BY THURSDAY  
EVENING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-00Z UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
SIMILAR TO YESTERDAY, THERE CONTINUES TO BE GOOD AGREEMENT WITH  
THIS SYSTEM. THERE HAVE BEEN SOME MODELS THAT HAVE TRENDED A BIT  
SLOWER COMPARED TO YESTERDAY'S RUNS, BUT ENSEMBLES CONTINUE TO  
SHOW RELATIVELY GOOD AGREEMENT, LED BY THE CONSISTENT ECMWF MEAN.  
ONLY THE 00Z UKMET APPEARS TO DEVIATE FROM THE LATEST  
DETERMINISTIC MODELS WITH A STRONGER SURFACE LOW ALONG/OFFSHORE OF  
THE WEST COAST ON FRIDAY INTO SATURDAY. FOR THAT REASON, A NON-00Z  
UKMET BLEND IS RECOMMENDED FOR 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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