571  
FXUS10 KWNH 211641  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1138 AM EST SUN JAN 21 2018  
 
VALID JAN 21/1200 UTC THRU JAN 25/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..DEEP LAYER CYCLONE OVER THE FOUR CORNERS REGION TODAY
 
   
..ENERGY/SURFACE LOW CROSSING THE PLAINS ON MONDAY
 
   
..LIFTING ACROSS THE GREAT LAKES AND NORTHEAST THROUGH TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE OVERALL IN VERY GOOD AGREEMENT WITH THE DETAILS OF  
THE DEEP CLOSED LOW OVER THE FOUR CORNERS REGION WHICH WILL LIFT  
NORTHEAST ACROSS THE CENTRAL PLAINS THROUGH MONDAY ALONG WITH A  
STRENGTHENING AREA OF LOW PRESSURE. THE SYSTEM WILL CROSS THE MID  
MS VALLEY MONDAY NIGHT AND THEN LIFT ACROSS PARTS OF THE GREAT  
LAKES AND NORTHEAST THROUGH TUESDAY. THE 12Z NAM IS PERIODICALLY  
APPEARING TO BE A TAD TOO DEEP IN THE 500/700 MB LAYER AS THE  
SYSTEM APPROACHES AND THEN CROSSES THE MID MS VALLEY...BUT  
OTHERWISE THE GUIDANCE IS IN GOOD AGREEMENT WITH THE EVOLUTION OF  
THIS SYSTEM THROUGH THE PERIOD. THEREFORE...WILL SUGGEST A GENERAL  
MODEL BLEND AT THIS TIME.  
 
   
..BROAD TROUGH QUICKLY CROSSING THE SOUTHEAST TODAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM CROSSING THE  
EASTERN GULF COAST REGION AND SOUTHEAST U.S. THROUGH THIS  
AFTERNOON BEFORE THEN DAMPENING OUT/WEAKENING OFFSHORE THE  
SOUTHEAST TONIGHT AND MONDAY. A GENERAL MODEL BLEND WILL BE  
PREFERRED.  
 
   
..UPPER TROUGH INITIALLY OFFSHORE BRITISH COLUMBIA
 
   
..ENERGY DIGGING ACROSS THE PLAINS/UPPER MIDWEST BY TUESDAY
 
   
..ARRIVING ACROSS THE OH VALLEY ON WEDNESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND...THROUGH 60 HOURS  
NON-GFS CONSENSUS...AFTER 60 HOURS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
AN UPPER TROUGH INITIALLY OFFSHORE BRITISH COLUMBIA TODAY WILL  
IMPACT THE PACIFIC NORTHWEST THROUGH TONIGHT AND THEN ADVANCE OUT  
ACROSS THE NORTHERN ROCKIES AND HIGH PLAINS THROUGH MONDAY.  
THEREAFTER...THE ENERGY SHOULD BEGIN TO DIG SOUTHEAST ACROSS THE  
MIDWEST THROUGH TUESDAY IN RESPONSE TO THE UPSTREAM RIDGING OVER  
THE GREAT BASIN. THE MODELS ARE IN GOOD AGREEMENT WITH THEIR MASS  
FIELD TIMING AND DEPTH THROUGH ABOUT 60 HOURS WITH THIS SYSTEM.  
THEREAFTER...THE 12Z GFS SUGGESTS A MORE PROGRESSIVE SOLUTION AND  
TENDS TO OUTRUN THE OTHER MODELS AS THE ENERGY ARRIVES ACROSS THE  
OH VALLEY. THE LATEST GEFS MEAN AND ECENS MEAN SUGGEST THE  
OPERATIONAL GFS IS A TAD TOO PROGRESSIVE...AND SO WILL PREFER A  
GENERAL MODEL BLEND THROUGH 60 HOURS AND THEN A NON-GFS CONSENSUS  
AFTER 60 HOURS.  
 
   
..SHORTWAVE IMPACTING THE PACIFIC NORTHWEST ON TUESDAY
 
   
..ATTENDANT SURFACE LOW LIFTING UP OFFSHORE BRITISH COLUMBIA
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW A SHORTWAVE ARRIVING ACROSS ESPECIALLY COASTAL  
AREAS OF THE PACIFIC NORTHWEST ON TUESDAY WITH THE SYSTEM THEN  
DAMPENING OUT AS IT ENCOUNTERS A DEVELOPING RIDGE OVER THE GREAT  
BASIN. THIS WILL DRIVE A FOCUS OF STRONGER SOUTH/SOUTHWEST FLOW UP  
ALONG THE COASTAL RANGES OUT AHEAD OF A STRONG AREA OF LOW  
PRESSURE THAT LIFTS UP OFFSHORE BRITISH COLUMBIA. THE MODELS ARE  
IN GOOD AGREEMENT WITH THIS SYSTEM AS IT ARRIVES AND SO A GENERAL  
MODEL BLEND WILL BE PREFERRED.  
 
   
..DEEP UPPER TROUGH OFFSHORE THE WEST COAST BY WEDNESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 06Z GEFS MEAN AND 00Z ECENS MEAN  
CONFIDENCE: AVERAGE  
 
THE MODELS ALLOW A DEEP UPPER TROUGH TO EVOLVE OFFSHORE THE WEST  
COAST THROUGH TUESDAY AND WEDNESDAY WITH STRONG SOUTHWEST ONSHORE  
FLOW SETTING UP SOUTH OF AN APPROACHING AREA OF LOW PRESSURE WHICH  
WILL BE APPROACHING COASTAL WA/OR BY LATE WEDNESDAY. THERE ARE  
SOME DETAIL DIFFERENCES WITH THE STRENGTH AND POSITION OF THE AXIS  
OF HEIGHT FALLS. THE 00Z ECMWF AND 12Z NAM TEND TO HAVE THEIR  
STRONGEST HEIGHT FALLS NORTH OF THE 12Z GFS AND 00Z UKMET BY THE  
END OF THE PERIOD. THE 00Z CMC OVERALL APPEARS TOO WEAK WITH THE  
TROUGHING IN GENERAL AS IT MAINTAINS MUCH MORE ENERGY FARTHER  
NORTH TOWARD THE GULF OF AK. AT THE SURFACE...THE MODELS HAVE A  
LOW APPROACHING THE PACIFIC NORTHWEST AS SHORTWAVE ENERGY ROUNDS  
THE BASE OF THE MEAN TROUGH AXIS/CLOSED LOW. THE ECMWF IS SOUTH OF  
EVERY MODEL BY LATE WEDNESDAY. THE NAM/GFS/CMC AND UKMET ARE  
CLUSTERED A BIT FARTHER NORTH OFFSHORE WA STATE BY  
COMPARISON...WITH THE UKMET OVERALL THE FARTHEST OFFSHORE. THE  
LATEST ECMWF IS WELL SOUTH OF THE ECENS MEAN AND BOTH THE GEFS  
MEAN AND ECENS MEAN TEND TO FAVOR A SOLUTION CLOSER TO THE GFS-LED  
CONSENSUS. THE GFS COULD BE A TAD TOO STRONG WITH ITS LOW CENTER  
THOUGH BASED ON THE ENSEMBLE SUITES OF GUIDANCE. WILL SUGGEST A  
COMPROMISE AMONG THE ENSEMBLE MEANS AT THIS POINT...AND  
SPECIFICALLY THE 06Z GEFS MEAN AND 00Z ECENS MEAN.  
 
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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