550  
FXUS10 KWNH 111611  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1110 AM EST SUN FEB 11 2018  
 
VALID FEB 11/1200 UTC THRU FEB 15/0000 UTC  
 
   
..SEE NOUS42 KWNO (ADMNFD) FOR STATUS OF THE UPPER AIR INGEST
 
 
   
..12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES/CONFIDENCE
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...DEPARTING LOW PRESSURE SYSTEM MOVING QUICKLY NORTHEAST TO NEAR  
LABRADOR BY MONDAY AFTERNOON...  
...TRAILING COLD FRONT LARGELY EXITING THE EASTERN SEABOARD BY  
MONDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
OVER THE NEXT 24 HOURS, MODEL MASS FIELDS ARE IN EXCELLENT  
AGREEMENT OVERALL, AND A GENERAL MODEL BLEND IS PREFERRED WITH  
HIGH CONFIDENCE. HOWEVER, AS THE SURFACE HIGH BUILDS INTO THE  
GREAT LAKES IN THE WAKE OF THE DEPARTING LOW, THE 12Z NAM IS FAR  
MORE EXPANSIVE WITH THE HIGH THAN ANY OTHER MODELS ACROSS MUCH OF  
THE EASTERN CONUS AND GULF OF MEXICO, WITH MSLP AS MUCH AS 2-3MB  
HIGHER THAN THE CONSENSUS OF OTHER MODELS. THE PREFERENCE,  
THEREFORE, IS TO EXCLUDE THE NAM FROM THE BLEND FOR THIS SYSTEM,  
DESPITE FAIRLY GOOD AGREEMENT IN THE FIRST 12-24 HOURS.  
 
...SHARPLY DIGGING SHORTWAVE TROUGH ALONG THE WEST COAST  
AMPLIFYING INTO A LARGE, POSITIVE-TILT TROUGH OVER THE WESTERN US  
BY TUESDAY...   
..SURFACE LOW IN THE GREAT BASIN MONDAY-TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS, 00Z ECMWF, UKMET  
CONFIDENCE: AVERAGE  
 
AS THE SHORTWAVE SHARPLY DIGS ALONG THE PACIFIC NORTHWEST COAST  
TODAY, SETTING UP FURTHER TROUGH AMPLIFICATION TOMORROW AND THE  
DEVELOPMENT OF A CLOSED LOW ON TUESDAY, MODEL AGREEMENT IS FAIRLY  
GOOD OVERALL. DIFFERENCES IN THE MODEL MASS FIELDS MOSTLY EMERGE  
ON WEDNESDAY, AND RELATE TO HOW FAST THE TROUGH BEGINS TO  
DEAMPLIFY AND EJECT EAST INTO THE WESTERN US. INCREASING HEIGHT  
FALLS IN THE NORTHWEST AS THE NEXT DIGGING WAVE ARRIVES WILL  
CONTRIBUTE, BUT GIVEN THE SIZE OF THE TROUGH AND ASSOCIATED CLOSED  
LOW NEAR THE CALIFORNIA COAST, THE PREFERENCE IS TO TREND TO THE  
SLOWER MODEL SOLUTIONS. IN THIS CASE THAT MEANS A PREFERENCE  
TOWARD THE GFS, ECMWF AND UKMET. THE 12Z NAM AND 00Z CMC DEAMPLIFY  
THE TROUGH AND EJECT IT EAST FASTER, BUT THE TENDENCY FOR LARGE,  
CLOSED LOWS ALOFT IS FOR THEM TO DEVOLVE SLOWLY. THE GEFS AND  
ECMWF ENSEMBLE MEANS ARE ALSO REASONABLY CLOSE TO THE GFS AND  
ECMWF TO LEND MORE ROBUST SUPPORT TO THE SLOWER SOLUTION.  
ADDITIONAL DIFFERENCES EXIST BETWEEN THE GFS, ECMWF, AND UKMET IN  
THE PLACEMENT AND DETAILS WITH THE UPPER LEVEL LOW, BUT CONFIDENCE  
IS NOT HIGH ENOUGH IN ANY ONE SCENARIO FOR IT TO BE CLEARLY  
PREFERRED.  
 
...SOUTHWARD SHIFT IN NORTHERN STREAM JET OVER CANADA  
TUESDAY-WEDNESDAY WITH NEXT SHOT OF ARCTIC AIR...   
..SHORTWAVE DIGGING INTO THE PACIFIC NORTHWEST TUESDAY NIGHT
 
 
...ADDITIONAL SHORTWAVES EJECTING ACROSS THE NORTHERN TIER OF  
STATES AS JETS BEGIN TO PHASE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 00Z ECMWF, EC ENS MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
MODELS GENERALLY SHOW A SIMILAR AMPLITUDE AND WAVELENGTH OF THIS  
DIGGING WAVE, AND THUS THE PRIMARY DIFFERENCES APPEAR TO BE  
RELATED TO TIMING. THE 00Z CMC APPEARS TO BE THE FASTEST, WHILE  
THE 12Z GFS APPEARS TO BE THE SLOWEST. THE ENSEMBLE MEANS (GEFS,  
ECMWF, AND CMC) LIE IN THE MIDDLE, AND ARE CLOSEST TO THE THE 00Z  
ECMWF (AND SECONDARILY THE 00Z UKMET AND 12Z NAM). THIS ALSO  
TRANSLATES TO SIMILAR TIMING DIFFERENCES WITH THE ARCTIC COLD  
FRONT THAT WILL BE PUSHING SOUTH THROUGH THE CANADIAN PRAIRIES ON  
WEDNESDAY. THE 12Z GFS IS ALSO SLOWEST THERE, WITH A SURFACE LOW  
POSITION GENERALLY TO THE NORTHEAST OF OTHER AVAILABLE MODELS. THE  
00Z ECMWF HAS THE BEST SUPPORT FROM OTHER GLOBAL MODELS, AND IS  
VERY CONSISTENT WITH THE POSITIONING OF SYNOPTIC FEATURES WITH ITS  
ENSEMBLE MEAN. THEREFORE, THE PREFERENCE IS FOR A BLEND OF THE 00Z  
ECMWF AND 00Z ECMWF ENSEMBLE MEAN.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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