357  
FXUS10 KWNH 041630  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1129 AM EST SUN MAR 04 2018  
 
VALID MAR 04/1200 UTC THRU MAR 08/0000 UTC  
 
===================================================  
12Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES  
==================================================  
 
...MEAN TROUGH EXITING THE MID-ATLANTIC / NORTHEAST STATES THROUGH  
MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~  
PREFERENCE: 12Z GFS AND 12Z NAM  
 
IN THE WAKE OF THE DEEPLY OCCLUDED STORM OFF THE EAST COAST, A  
SMALL SCALE SHORTWAVE TROUGH IS FORECAST TO DIVE ACROSS THE  
NORTHEAST AND MID-ATLANTIC TODAY, REINVIGORATING THE BASE OF THE  
LARGER SCALE TROUGH OFFSHORE BEFORE THE NEXT UPSTREAM SYSTEM  
STARTS TO TAKE CENTER STAGE. GENERALLY SPEAKING, THERE ARE SOME  
REASONS TO FAVOR THE NCEP CAMP OF MODELS REGARDING MANY OF THE  
SHORTWAVE DETAILS WITHIN THE BLOCKY NORTHERN LATITUDES AND  
SEMI-PROGRESSIVE MORE SOUTHERLY LATITUDES (SEE CENTRAL U.S.  
SECTION BELOW). WHEN THE 12Z NAM TRENDED SLOWER AND DEEPER WITH  
THE AFORE-MENTIONED SHORTWAVE DIVING ACROSS THE NORTHEAST, AND THE  
GFS THEN FULLY SUPPORTED THIS TREND, THERE APPEAR TO BE PLENTY OF  
REASONS TO FAVOR A NAM/GFS BLEND FOR THIS SYSTEM. THE 00Z ECMWF  
CERTAINLY APPEARED TOO FAST, OR WAS THE FASTEST OF THE MAJOR  
OPERATIONAL MODELS.  
 
...CENTRAL U.S. STORM PASSING OFF TO DEVELOPING NOR'EASTER BY  
WEDNESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS...SUPPORTED BY 00Z/06Z GFS CONTINUITY, 06Z  
GEFS MEAN, AND TO LESSER EXTENT THE NAM  
 
A MEDIUM WAVELENGTH SYSTEM EJECTING AT A NEGATIVE TILT INTO THE  
PLAINS WILL DRIVE A WINTER STORM AND, IN SOME CASES, BLIZZARD  
CONDITIONS, ACROSS THAT REGION THROUGH MONDAY NIGHT / TUESDAY. THE  
STORM THEN GOES THROUGH A FAIRLY INTERESTING EVOLUTION WHICH THE  
MODELS AGREE SHOULD LEAD TO A HAND-OFF TO COASTAL LOW PRESSURE  
DEVELOPMENT AND A POTENTIAL NOR'EASTER MID WEEK. THE MATURE  
CYCLONE OVER THE PLAINS/MIDWEST BY TUESDAY WILL SIT BENEATH A  
BLOCKY PATTERN IN PLACE ACROSS THE FULL BREADTH OF CANADA, BUT  
WITHIN WHAT COULD LOOSELY BE TERMED A PROGRESSIVE FLOW PATTERN AT  
THE LATITUDES OF THE UNITED STATES, DESCRIBING THE FLOW FROM  
ROUGHLY BRITISH COLUMBIA TO THE CENTRAL U.S. TO THE WESTERN  
ATLANTIC. THE MATURE CYCLONE IS FORECAST TO BE URGED ALONG BY  
ENERGY DROPPING DOWN THE BACK SIDE OF THE BACK SIDE OF THE UPPER  
TROUGH, PUSHING HEIGHT FALLS TO THE SOUTH AND EAST, WHILE A SORT  
OF UNCONVENTIONAL KICKER SYSTEM OPENS UP THE TROUGH FROM THE NORTH  
SIDE / ONTARIO AND GREAT LAKES / ALLOWING IT ONCE AGAIN TO PIVOT  
AROUND TO A NEGATIVE TILT AS IT REACHES THE EAST COAST ON  
WEDNESDAY.  
 
MODELS AGREE TO THESE CONCEPTS, BUT WHEN CONSIDERING THE DETAILS,  
WPC PREFERRED THE MORE PRONOUNCED CYCLONIC FLOW OVER THE CENTRAL  
HIGH PLAINS STATES ON THE BACK SIDE OF THE CYCLONE, AS WELL AS  
SHARPER TROUGHING INTO THE HEIGHT WEAKNESS OVER THE OFFSHORE  
WATERS OF BRITISH COLUMBIA. THIS TENDED TO REMOVE THE 00Z ECMWF  
FROM CONSIDERATION, AND TO LESSER EXTENT THE UKMET, ESPECIALLY BY  
DAY 3. THE 00Z CANADIAN DID NOT APPEAR PARTICULARLY HELPFUL, AND  
WAS SOMEWHAT OUT OF PHASE ALONG THE EAST AND WEST COASTS BY DAY 3.  
THIS LEAVES US FAVORING THE NCEP... GFS/NAM CAMP. FORTUNATELY, THE  
GFS SHOWED GOOD CONTINUITY BETWEEN 00Z, 06Z, AND 12Z RUNS, AS WELL  
AS GOOD SUPPORT FROM THE 06Z GEFS MEAN. THIS HELPS BOOST OUR  
CONFIDENCE IN RECOMMENDING THE GFS AS A MAJORITY BASIS FOR THE  
SHORT TERM FORECAST. THE 12Z NAM, WHILE USUALLY NOT THE BEST MODEL  
FOR THE DETAILS BEYOND DAY 1, IS REASONABLY CLOSE TO THE GFS FOR  
MANY ASPECTS OF THE FLOW, AND COULD BE USED, ALTHOUGH WE WOULD  
MORE STRONGLY RECOMMEND THE GFS.  
 
   
..WEST COAST / NORTHWEST / NORTHERN ROCKIES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS/NAM WITH THE 06Z GFS  
 
SYNOPTIC REASONING APPLIED TO THE FLOW REGIME FROM THE EASTERN  
PACIFIC TO THE ATLANTIC LED WPC TO FAVOR THE GFS AS A BASIS FOR  
THE SHORT RANGE FORECAST (SEE PREVIOUS SECTIONS). IN THE WEST, THE  
12Z GFS MAY BE OVER-AMPLIFYING A SHORTWAVE WITHIN THE EASTERN  
PORTION OF THE POSITIVELY TILTED TROUGH BY THE END OF DAY 3, AS IT  
APPROACHES THE AREA OFF NORTHERN CA AND SOUTHWEST OREGON. BLENDING  
WITH THE 12Z NAM AND 06Z GFS WOULD PROVIDE A BETTER CONSENSUS  
SOLUTION MORE IN LINE WITH THE RELATIVE CONFIDENCE GIVEN A FAIR  
AMOUNT OF SPREAD AMONG THE OPERATIONAL MODELS. HERE, AS WELL AS  
ELSEWHERE ON THE MAP, HOWEVER, THE 06Z GEFS DOES OFFER GOOD  
SUPPORT TO THE RECENT OPERATIONAL GFS RUNS AND THE 12Z NAM.  
 
PREVIOUS MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
PREVIOUS 500 MB FORECASTS AT  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
BURKE  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page