699  
FXUS10 KWNH 041847  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
147 PM EST SUN MAR 04 2018  
 
VALID MAR 04/1200 UTC THRU MAR 08/0000 UTC  
 
===========================================  
FINAL 12Z MODEL EVALUATION AND PREFERENCES  
===========================================  
 
...MEAN TROUGH EXITING THE MID-ATLANTIC / NORTHEAST STATES THROUGH  
MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z OPERATIONAL MODELS, EXCLUDING THE  
UKMET  
CONFIDENCE: AVERAGE  
 
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 APPEARED TO BE PLENTY  
OF REASONS TO FAVOR A NAM/GFS BLEND FOR THIS SYSTEM. THE 12Z ECMWF  
AND CANADIAN THEN TRENDED IN LINE WITH THE NCEP GUIDANCE. ONLY THE  
UKMET STANDS OUT AS BEING TOO FAST WITH THIS BACK-SIDE SHORTWAVE.  
 
...CENTRAL U.S. STORM PASSING OFF TO DEVELOPING NOR'EASTER BY  
WEDNESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS...SUPPORTED BY 00Z/06Z GFS CONTINUITY, 12Z  
GEFS MEAN, AND TO LESSER EXTENT THE NAM  
CONFIDENCE: AVERAGE  
 
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 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 WPC THINKING WAS MORE IN LINE WITH THE  
NCEP GUIDANCE... 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 AND NOW 12Z GEFS MEAN. FURTHERMORE, THE 12Z  
GLOBAL MODEL CONSENSUS WAS TOWARD THE WPC PREFERRED PATTERN OVER  
THE HIGH PLAINS AND OFF OF BRITISH COLUMBIA, INCLUDING THE 12Z  
ECMWF. 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.  
THE 12Z RUN OF THE ECMWF LOOKS LIKE A MUCH MORE VIABLE SOLUTION  
THAN THE 00Z RUN HAD BEEN, BUT IS STILL DISPLAYING A SYSTEMATIC  
TENDENCY TO BE QUICK IN DROPPING THE KICKER SYSTEM SOUTHWESTWARD  
THROUGH ONTARIO, AND A TENDENCY TO INDICATE A VERY RAPID  
PROGRESSION OF THE DEEPENING EAST COAST CYCLONE ON DAY 3. THESE  
TENDENCIES STILL HAVE A DEGREE OF SUPPORT FROM THE UKMET, BUT THE  
OVERALL TREND HAS BEEN TOWARD A MORE GFS-LIKE EVOLUTION. WHILE  
THERE ARE NO TRUE OUTLIERS AND A CONSENSUS APPROACH COULD BE USED,  
WE THINK THERE ARE SOME REASONS TO PREFER THE GFS.  
 
   
..WEST COAST / NORTHWEST / NORTHERN ROCKIES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z OPERATIONAL MODELS  
CONFIDENCE: AVERAGE  
 
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 OTHER 12Z OPERATIONAL GUIDANCE, ALL OF WHICH WAS "IN THE  
BALLPARK" AT THE SURFACE AND ALOFT, IS RECOMMENDED TO DERIVE A  
MORE CONFIDENT CONSENSUS SOLUTION.  
 
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  
 

 
 
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