578  
FXUS10 KWNH 271839  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
138 PM EST SAT JAN 27 2018  
 
VALID JAN 27/1200 UTC THRU JAN 31/0000 UTC  
 
..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION ALONG WITH LATEST MODEL PREFERENCES/CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..WEAKENING SHORTWAVE CROSSING THE WESTERN GULF COAST TODAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS HANDLE THE SYSTEM SIMILARLY TODAY THROUGH TONIGHT AS IT  
MOVES EAST AND DAMPENS OUT WITH TIME.  
 
   
..SHORTWAVE TROUGH/COLD FRONT OVER THE GREAT LAKES/MIDWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW A NORTHERN STREAM SHORTWAVE TROUGH CROSSING  
PORTIONS OF THE NORTHERN PLAINS AND THE UPPER MIDWEST THROUGH  
TONIGHT AND THEN CROSSING THE GREAT LAKES REGION THROUGH SUNDAY.  
MODEL SPREAD IS RATHER MINIMAL WITH THIS SYSTEM, AND SO A GENERAL  
MODEL BLEND WILL BE PREFERRED.  
 
   
..EVOLVING LONGWAVE TROUGH OVER THE EASTERN U.S. BY TUESDAY
 
   
..SURFACE LOW EVOLUTION OFFSHORE THE MID-ATLANTIC/NEW ENGLAND
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GEFS MEAN AND 00Z ECENS MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE MODELS TAKE A RELATIVELY WEAK SOUTHERN STREAM TROUGH OUT OF  
THE SOUTHERN PLAINS AND ALLOW IT TO CROSS THE GULF COAST STATES  
THROUGH SUNDAY WHICH WILL HELP TO DRIVE AN AREA OF LOW PRESSURE  
ALONG A COLD FRONT ADVANCING INTO THE EASTERN U.S. MEANWHILE THERE  
WILL BE AN INTRUSION OF NORTHERN STREAM SHORTWAVE ENERGY CROSSING  
THE MIDWEST THAT WILL BE DIGGING SOUTHEAST THROUGH THE OHIO AND  
TENNESSEE VALLEYS THROUGH MONDAY. THE TWO STREAMS WILL ATTEMPT TO  
PHASE ALONG THE EAST COAST BY LATER MONDAY AND WILL LIKELY LEAD TO  
THE DEVELOPMENT OF A LONGWAVE TROUGH OVER THE EASTERN U.S. THAT  
WILL TAKE ON A NEUTRAL TO NEGATIVE TILT. THE AFOREMENTIONED LOW  
PRESSURE WAVE WHICH WILL BE OVER THE GULF COAST STATES SHOULD LIFT  
NORTHEAST AND REDEVELOPMENT OVER THE MID-ATLANTIC COASTAL PLAIN  
SUNDAY NIGHT AND THEN MOVE OFFSHORE THE DELMARVA BEFORE THEN  
INTENSIFYING EAST OF NEW ENGLAND MONDAY NIGHT. THE 12Z UKMET AND  
12Z CMC HAVE TENDED TO TREND SOMEWHAT TOWARD THE 00Z/12Z ECMWF  
SOLUTIONS WHICH DEPICT A BIT MORE OF A NEGATIVELY TILTED TROUGH  
ALONG THE EAST COAST. THIS ADDED ENERGY IN THE BASE OF THE TROUGH  
ALSO ALLOWS FOR THE DEEPENING LOW PRESSURE OFF THE EAST COAST TO  
BE A BIT SLOWER TO LIFT AWAY TO THE NORTHEAST. THE 00Z ECENS MEAN  
SUPPORTS THIS CAMP. MEANWHILE, THE 12Z NAM AND 12Z GFS ALONG WITH  
THE 12Z GEFS MEAN SUPPORT THE IDEA OF LOW PRESSURE LIFTING A BIT  
MORE PROGRESSIVELY AWAY FROM THE MID-ATLANTIC AND NEW ENGLAND.  
GIVEN THE TWO MODEL CAMPS AND RELATIVELY INCREASED MODEL SPREAD,  
AN ATTEMPT TO COMPROMISE WILL BE SUGGESTED BY BLENDING THE GEFS  
MEAN AND ECENS MEAN.  
 
   
..LARGE UPPER TROUGH/CLOSED LOW IMPACTING THE NORTHWEST
 
   
..SURFACE LOW NEAR THE U.S./CANADIAN BORDER MOVING EAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS BRING A ROBUST UPPER TROUGH INTO THE PACIFIC NORTHWEST  
BY LATER MONDAY AND TUESDAY AS A STRONG CLOSED LOW WRAPS UP OVER  
THE GULF OF ALASKA. THE UPPER TROUGH AND ASSOCIATED COLD FRONT  
WILL MOVE INLAND AND CROSS THE NORTHERN ROCKIES BEFORE THEN  
EJECTING EAST ACROSS THE NORTHERN PLAINS. A STRONG AREA OF LOW  
PRESSURE WITH THIS SYSTEM WILL TRAVERSE SOUTHERN CANADA JUST TO  
THE NORTH OF THE U.S./CANADIAN BORDER. THE 12Z UKMET APPEARS TO BE  
JUST A TAD TOO PROGRESSIVE, WITH THE 12Z NAM AND 12Z CMC A BIT TOO  
SLOW. THE 12Z GFS AND 12Z ECMWF BEST APPROXIMATE THE MODEL  
CONSENSUS AND ARE WELL CLUSTERED, SO WILL PREFER A BLEND OF THESE  
TWO SOLUTIONS.  
 
   
..SHORTWAVE APPROACHING THE PACIFIC NORTHWEST LATE TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM CONSENSUS  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ALLOW ANOTHER SHORTWAVE TO APPROACH THE PACIFIC  
NORTHWEST AND ADJACENT AREAS OF BRITISH COLUMBIA BY LATE TUESDAY.  
THE 12Z NAM IS SOMEWHAT OF A STRONGER OUTLIER AS THE ENERGY  
APPROACHES BRITISH COLUMBIA, WITH THE REMAINING MODELS PRETTY WELL  
CLUSTERED WITH TIMING AND DEPTH. THUS A NON-NAM CONSENSUS WILL BE  
PREFERRED AT THIS TIME.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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