496  
FXUS10 KWNH 231644  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1143 AM EST TUE JAN 23 2018  
 
VALID JAN 23/1200 UTC THRU JAN 27/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...BROAD OCCLUDED CYCLONE AND ASSOCIATED TROUGH OVER THE NORTHEAST  
PROGRESSING TO NEAR LABRADOR BY WEDNESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS ARE IN EXCELLENT AGREEMENT WITH THE EVOLUTION OF THIS  
SYSTEM OVER THE NEXT 24 HOURS AS IT MOVES OUT OF THE NORTHEAST  
REGION. AVAILABLE OPERATIONAL MODELS SHOW TIGHT CLUSTERING WITH  
THE LOW POSITION AND LIMITED SPREAD WITH MANY OF THE MASS FIELDS.  
THEREFORE, A GENERAL MODEL BLEND IS PREFERRED WITH ABOVE AVERAGE  
CONFIDENCE.  
 
...NORTHERN PLAINS SHORTWAVE AND ASSOCIATED SECONDARY COLD FRONT  
MOVING QUICKLY EAST TO THE EAST COAST BY WED NGT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THERE ARE SOME INITIAL DIFFERENCES ACROSS THE NORTHERN PLAINS, BUT  
IT APPEARS TO HAVE VERY LITTLE IMPACT ON THE MODEL SCENARIOS  
THROUGH THE NEXT 24-36 HOURS AS THE TROUGH PROGRESSES QUICKLY TO  
THE EAST. THE 12Z GFS INITIALIZED WITH SLIGHTLY LOWER HEIGHTS  
ACROSS MUCH OF THE NORTHERN PLAINS THAN OTHER MODELS, BUT IT STILL  
SHOWS A VERY SIMILAR AMPLITUDE AND TIMING OF THE WAVE BY 25/06Z  
(WEDNESDAY NIGHT). IT DOES SHOW SLIGHTLY FASTER TIMING OF THE  
COLDER AIR OVER THE MID ATLANTIC, BUT OVERALL IS REASONABLY CLOSE  
TO OTHER MODELS. THEREFORE, A GENERAL MODEL BLEND IS PREFERRED  
WITH THIS SYSTEM.  
 
...PROGRESSIVE TROUGH PUSHING ONTO THE WEST COAST WED AND  
DEAMPLIFYING AS IT PUSHES EAST TO THE GREAT LAKES BY FRI...  
...ASSOCIATED SURFACE LOW NEAR THE CANADIAN BORDER AND TRAILING  
COLD FRONT PUSHING INTO THE CENTRAL US...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS, 00Z ECMWF  
LEAN TO ECMWF (65%) VS GFS (35%)  
CONFIDENCE: AVERAGE  
 
THE 12Z GFS AND 00Z ECMWF OFFER FAIRLY SIMILAR SCENARIOS THROUGH  
THE FIRST THREE DAYS OF THE FORECAST, WITH THE MOST NOTABLE  
DIFFERENCES EMERGING LATE IN THE PERIOD OVER THE PLAINS. DESPITE A  
SIMILAR LOW POSITION BY 27/00Z (FRIDAY EVENING), THE GFS HAS  
FASTER TIMING OF THE COLD FRONT IN THE PLAINS, WHILE THE ECMWF IS  
SLOWER, AND IN BETTER AGREEMENT WITH MOST OF THE OTHER MODELS.  
EVEN THE GEFS MEAN (06Z RUN) IS SLOWER THAN THE OPERATIONAL GFS.  
GIVEN THE NEUTRAL OR DEAMPLIFYING TREND OF THE TROUGH THROUGH THE  
PERIOD, DO NOT ANTICIPATE AN ACCELERATING COLD FRONT DOWN THE  
PLAINS AS WE SOMETIMES SEE IN WINTER. THEREFORE, THE BLEND  
PREFERENCE IS WEIGHTED MORE TOWARD THE ECMWF, PARTICULARLY AT  
LATER HOURS.  
 
THE 00Z CMC WAS NOT INCLUDED AS IT SUPPRESSES THE HEIGHT FALLS  
FURTHER WEST AND OFFSHORE INITIALLY ALONG THE PACIFIC NORTHWEST  
COAST, WHICH LEADS TO A FLATTER WAVE, A WEAKER SURFACE LOW THAT IS  
SITUATED ON THE SOUTHERN END OF MODEL SPREAD. THE 00Z UKMET WAS  
ALSO NOT INCLUDED, AS IT SHOWS A STRONGER SURFACE LOW (POSITION  
FURTHEST SOUTH OF ANY MODEL), WITH NOTEWORTHY TROUGH AMPLIFICATION  
OVER THE PLAINS -- UNSUPPORTED BY ANY OTHER MODEL. AND ALTHOUGH  
THE 12Z NAM IS NOT SIGNIFICANTLY DIFFERENT WITH THE TIMING OR  
POSITION OF THE TROUGH OR SURFACE LOW, IT DOES HAVE A COLD BIAS IN  
THE NORTHWEST BEHIND THE COLD FRONT, WHICH COULD LEAD TO LOWER  
FORECAST SNOW LEVELS THAN WOULD BE SUGGESTED BY OTHER MODELS.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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