408  
FXUS10 KWNH 061915  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
215 PM EST TUE MAR 06 2018  
 
VALID MAR 06/1200 UTC THRU MAR 10/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...ALONG WITH FINAL 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: NON 12Z GFS BLEND  
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 AND THEN  
SLIGHTLY EAST WITH ITS 12Z/06 CYCLE.  
 
THE STRENGTH LOOKS SIMILAR REGARDING THE SURFACE TO 500 MB LOWS 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 12Z ECMWF/UKMET/CMC DO NOT.  
 
CONSIDERING ONLY MINOR TRENDS IN THE GUIDANCE THROUGH TODAY'S 12Z  
CYCLE, THE 12Z GFS SURFACE LOW TRACK LOOKS TO BE ON THE WESTERN  
SIDE OF THE AVAILABLE MODEL SPREAD WHILE THE REMAINING 12Z  
GUIDANCE IS SIMILAR TO ONE ANOTHER. THE RESULT IS A WARMER SURFACE  
TO 850 MB LAYER IN THE 12Z GFS COMPARED TO THE REMAINING GUIDANCE.  
A GROWING CONSENSUS SEEMS TO BE FOR A NON 12Z GFS SOLUTION FOR  
THIS SYSTEM THROUGH THURSDAY.  
 
   
..SECONDARY SURFACE LOW NEAR NOVA SCOTIA FRIDAY NIGHT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z UKMET  
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. THE  
12Z ECMWF NUDGED EAST FROM ITS PREVIOUSLY FARTHER WEST 00Z CYCLE,  
BUT THE DIFFERENCES IS MINOR. THE 12Z UKMET AND 12Z CMC TRENDED  
WESTWARD FROM THEIR PREVIOUS CYCLES WITH THE 12Z UKMET NOW WEST OF  
THE 12Z NAM/GFS. HOWEVER, THE 12Z CMC IS NEARER TO THE 12Z NAM/GFS  
AND GIVEN THE LATEST ENSEMBLE GUIDANCE, THE 12Z UKMET IS NEAREST  
TO THE 12Z GEFS MEAN AND 00Z ECMWF MEAN WITH BOTH THE GEFS AND  
ECMWF MEANS NEAR ONE ANOTHER IN POSITION BY 00Z/10. THE PREFERENCE  
HAS SHIFTED WESTWARD TO THE 12Z UKMET WHICH IS A COMPROMISE  
POSITION BETWEEN THE WESTWARD AND EASTWARD LOW TRACKS.  
 
   
..WEST COAST/NORTHWESTERN U.S.
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL BLEND THROUGH 00Z/09  
12Z 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, AND THE 12Z ECMWF SLOWED  
SOMEWHAT FROM ITS PREVIOUSLY FASTER 00Z CYCLE AS THE SYSTEM COMES  
ASHORE EARLY THURSDAY MORNING. GIVEN THE 00Z ECMWF MEAN WAS SLOWER  
THAN THE 00Z ECMWF, THIS SHIFT BY THE 12Z ECMWF APPEARS TO BE IN  
THE RIGHT DIRECTION 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 12Z ECMWF APPEARS  
TO BE THE FAVORABLE MIDDLE GROUND WITH THE 12Z NAM FASTER THAN 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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