317  
FXUS10 KWNH 061730  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1229 PM EST TUE MAR 06 2018  
 
VALID MAR 06/1200 UTC THROUGH MAR 10/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION...ALONG WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
 
...SERIES OF SHORTWAVES IN THE VICINITY OF THE NORTHEAST U.S.  
CLOSED LOW...  
...DEVELOPING NORTHEAST COASTAL LOW WEDNESDAY AND WEDNESDAY  
NIGHT...   
..SECONDARY SURFACE LOW NEAR NOVA SCOTIA FRIDAY NIGHT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z NAM/00Z UKMET  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
REGARDING THE SURFACE LOW FORECAST TO TRACK NORTH ALONG THE  
NORTHEAST COAST ON WEDNESDAY AND WEDNESDAY NIGHT, ECMWF/GEFS/CMC  
ENSEMBLE TRENDS HAVE NOT SHOWN MUCH IN THE WAY WESTWARD/EASTWARD  
TRENDS SINCE YESTERDAY, BUT PERHAPS A SUBTLE SHIFT TO THE WEST  
VALID 00Z/08 AND 12Z/08. THE DETERMINISTIC GUIDANCE HAS ALSO ONLY  
SHOWN MINOR MOVEMENT SINCE YESTERDAY EXCEPT THE UKMET WHICH HAS  
TRENDED WEST SINCE YESTERDAY THROUGH ITS 00Z/06 CYCLE.  
 
THE STRENGTH OF THE SURFACE TO 500 MB LOWS LOOKS SIMILAR IN ALL OF  
THE GUIDANCE EXCEPT EARLY IN THE FORECAST REGARDING A SUB-5280 M  
LOW SITUATED OVER IOWA AT 12Z. THE 12Z NAM/GFS, RAP SHOW A 5280 M  
CONTOUR VALID 12Z/07 OVER THE OHIO VALLEY WHEREAS THE OLDER 00Z  
ECMWF/UKMET/CMC DO NOT. PERHAPS THIS IS ONE REASON WHY THE 12Z  
NAM/GFS ARE FARTHER WEST/INLAND WITH THE SURFACE LOW TRACK  
COMPARED TO THE 00Z ECMWF/UKMET/CMC? REGARDLESS OF THIS FACT, THE  
12Z GFS LOOKS TO BE ON THE WESTERN SIDE OF THE AVAILABLE MODEL  
SPREAD WHILE THE 00Z ECMWF AND 00Z CMC ARE MORE EAST.  
 
A FAVORABLE MIDDLE GROUND CONSIDERING ONLY MINOR TRENDS IS A BLEND  
OF THE 12Z NAM AND 00Z UKMET FOR THE SURFACE LOW TRACK THROUGH  
THURSDAY.  
 
   
..SECONDARY SURFACE LOW NEAR NOVA SCOTIA FRIDAY NIGHT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WHILE THE INITIAL SURFACE LOW IS IMPACTING NEW ENGLAND WEDNESDAY  
INTO THURSDAY, ANOTHER SURFACE LOW IS FORECAST TO DEVELOP OVER THE  
WESTERN ATLANTIC ON THURSDAY AND TRACK NORTH-NORTHEASTWARD.  
OUTSIDE OF THE FARTHER WEST 00Z ECMWF, THE DETERMINISTIC MODELS  
SHOW DECENT AGREEMENT HERE FOR A NON-00Z ECMWF BLEND. THERE IS  
MODEST SUPPORT FOR A 00Z ECMWF-LIKE SOLUTION, BUT UNTIL GREATER  
DETERMINISTIC GUIDANCE IS SEEN FOR THE WESTWARD 00Z ECMWF WITH  
THIS NEXT SURFACE LOW ON FRIDAY, A NON-00Z ECMWF BLEND WILL BE  
PREFERRED.  
 
   
..WEST COAST/NORTHWESTERN U.S.
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: NON 00Z ECMWF BLEND THROUGH 00Z/09  
00Z ECMWF BETWEEN 00Z/09 AND 00Z/10  
CONFIDENCE: AVERAGE  
 
TWO FEATURES ARE WORTH NOTING WHICH WILL IMPACT WEATHER ALONG THE  
WESTERN U.S. THROUGH FRIDAY. A CLOSED LOW IS EXPECTED TO WEAKEN  
OVER THE PACIFIC NORTHWEST ON THURSDAY, BUT THE 00Z ECMWF APPEARS  
TO BE A FASTER OUTLIER WITH THIS SYSTEM. THE 00Z ECMWF MEAN IS  
SLOWER THAN THE 00Z ECMWF AS WELL, SO THERE APPEARS TO BE GOOD  
SUPPORT FOR A NON 00Z ECMWF BLEND THROUGH 00Z/09 WHICH IS THE  
POINT AT WHICH THE SHORTWAVE WEAKENS CONSIDERABLY AS IT TRACKS  
OVER LAND.  
 
A SECOND SHORTWAVE IS EXPECTED TO DROP SOUTHWARD BRITISH COLUMBIA  
COAST ON THURSDAY AND INTERESTINGLY ENOUGH, THE 00Z ECMWF APPEARS  
TO BE THE FAVORABLE MIDDLE GROUND WITH THE 12Z NAM FASTER AND 12Z  
GFS SLOWER THAN THE FAVORED ENSEMBLE MEANS AND MIDDLE GROUND. THIS  
NEXT WAVE WILL IMPACT THE TIMING OF THE COLD FRONT DROPPING DOWN  
THE COAST OF OREGON AND CALIFORNIA.  
 
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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