052  
FXUS10 KWNH 191700  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EST FRI JAN 19 2018  
 
VALID JAN 19/1200 UTC THRU JAN 23/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SOUTHERN STREAM WAVE EJECTING NORTHEAST FROM THE GULF OF  
MEXICO...  
 
PREFERENCE: 12Z GFS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS TAKE THE SOUTHERN STREAM CLOSED LOW/TROUGH OVER THE  
WESTERN GULF COAST REGION GRADUALLY OFF TO THE EAST THROUGH THE  
WEEKEND WHICH WILL ALLOW IT TO TRAVERSE THE REMAINDER OF THE GULF  
COAST STATES. THE SYSTEM WILL WEAKEN AND BEGIN TO DAMPEN OUT BY  
SUNDAY NIGHT AND MONDAY AS IT REACHES THE SOUTHEAST COAST AND  
PUSHES OFFSHORE. BY LATER IN THE WEEKEND...THE 00Z UKMET/00Z CMC  
AND 00Z ECMWF SOLUTION ALL BECOME A LITTLE MORE PROGRESSIVE AND  
WEAKER THAN THE 12Z NAM/GFS SOLUTIONS. THE CMC OVERALL IS THE  
WEAKEST...WITH THE NAM THE STRONGEST BY SUNDAY AND MONDAY. THE GFS  
TENDS TO HAVE THE BETTER ENSEMBLE SUPPORT VIA THE 06Z GEFS MEAN  
AND EVEN THE 00Z ECENS MEAN TO AN EXTENT WHICH SUGGESTS THE ECMWF  
EVENTUALLY IS A BIT TOO PROGRESSIVE. WILL FAVOR THE GFS AT THIS  
TIME WITH THIS SYSTEM.  
 
   
..DEEPENING TROUGH MOVING INLAND ACROSS THE SOUTHWEST
 
   
..ENERGY EJECTING NORTHEAST ACROSS THE PLAINS/MIDWEST
 
   
..ATTENDANT SURFACE LOW LIFTING TOWARD THE GREAT LAKES
 
 
PREFERENCE: GENERAL MODEL BLEND...THROUGH 48 HOURS  
12Z GFS...AFTER 48 HOURS  
CONFIDENCE: AVERAGE  
 
THE GUIDANCE AGREES IN TAKING A SOUTHERN STREAM TROUGH ACROSS CA  
AND THROUGH THE SOUTHERN GREAT BASIN AND ADJACENT AREAS OF THE  
SOUTHWEST U.S. THROUGH SATURDAY. THE SYSTEM IS THEN EXPECTED TO  
AMPLIFY AND CLOSE OFF IN THE MID LEVELS OVER THE FOUR CORNERS  
REGION SATURDAY NIGHT BEFORE EJECTING OUT ACROSS THE  
CENTRAL/SOUTHERN HIGH PLAINS ON SUNDAY. THE STRONG HEIGHT FALLS  
WILL DRIVE A WELL-ORGANIZED AREA OF LOW PRESSURE IN THE LEE OF THE  
ROCKIES INVOLVING SOUTHEAST CO WHICH SHOULD THEN ADVANCE EAST  
ACROSS SOUTHERN KS AND THEN LIFT NORTHEAST TOWARD THE GREAT LAKES  
REGION SUNDAY NIGHT THROUGH MONDAY. THE MODEL MASS FIELD SPREAD IS  
RATHER MINIMAL AS THE ENERGY TRAVERSES THE SOUTHWEST AND BROADER  
FOUR CORNERS REGION...BUT AS THE SYSTEM REACHES THE  
CENTRAL/SOUTHERN PLAINS...THE 12Z NAM BECOMES STRONGER THAN ANY  
OTHER MODELS WITH ITS 500/700 MB REFLECTION AND TENDS TO LEAN A  
BIT TOWARD THE FASTER SIDE OF THE GUIDANCE. THE 00Z ECMWF  
MEANWHILE BECOMES THE SLOWEST SOLUTION AND IS ALSO A LITTLE SOUTH  
OF THE MODEL CONSENSUS WITH ITS CLOSED LOW EVOLUTION ACROSS THE  
MIDWEST THROUGH MONDAY. THE 12Z GFS IS A BIT FASTER AND ONLY A  
LITTLE SLOWER THAN THE NAM. THE 00Z UKMET AND 00Z CMC ARE IN  
BETWEEN THE SLOWER ECMWF AND FASTER GFS. THE 00Z ECENS MEAN  
STRONGLY SUGGESTS THE ECMWF IS TOO SLOW BY THE END OF THE  
PERIOD...AND THE 06Z GEFS MEAN IS A LITTLE FASTER THAN THE  
OPERATIONAL GFS AND SUGGESTS THE RELATIVELY FASTER NAM IS WITHIN  
THE REALM OF POSSIBILITIES. BASED ON ALL OF THIS...WILL SUGGEST A  
GENERAL MODEL BLEND THROUGH 48 HOURS...FOLLOWED BY A SOLUTION AT  
LEAST WEIGHTED STRONGLY TOWARD THE GFS THEREAFTER WITH MUCH  
LOWERING WEIGHTING GIVEN TO THE ECMWF AND NAM BY COMPARISON.  
 
   
..NORTHERN STREAM TROUGH CLIPPING THE NORTHERN PLAINS
 
 
PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A WEAKER NORTHERN STREAM TROUGH COMING IN OFF THE PACIFIC OCEAN  
TODAY WILL CROSS THE PACIFIC NORTHWEST AND TRAVERSE THE NORTHERN  
PLAINS THROUGH SUNDAY. THE 12Z GFS AND 00Z ECMWF ARE REASONABLY  
WELL CLUSTERED AND BEST APPROXIMATE THE MODEL CONSENSUS...AND SO A  
BLEND OF THE GFS AND ECMWF WILL BE PREFERRED.  
 
   
..UPPER TROUGH CROSSING INTO THE PACIFIC NORTHWEST BY SUNDAY
 
 
PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE NEXT UPPER TROUGH COMING ACROSS THE NORTHEAST PACIFIC WILL  
ARRIVE OVER THE NORTHWEST U.S. ON SUNDAY AND THEN BEGIN TO FLATTEN  
OUT BY MONDAY OVER THE GREAT BASIN AND NORTHERN ROCKIES. THE 12Z  
NAM TENDS TO BE THE STRONGEST OVERALL SOLUTION WITH THE TROUGH.  
MEANWHILE...THE 00Z UKMET GRADUALLY APPEARS TO BE TOO SLOW. BETTER  
MODEL CLUSTERING AND ENSEMBLE SUPPORT FAVORS THE 12Z GFS AND 00Z  
ECMWF...SO A BLEND OF THE GFS AND ECMWF WILL BE PREFERRED.  
 
 
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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