198  
FXUS10 KWNH 111641  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1141 AM EST THU JAN 11 2018  
 
VALID JAN 11/1200 UTC THRU JAN 15/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...CENTRAL US TROUGH WITH POTENT +PV ANOMALY AT THE BASE OVER  
TEXAS BEGINNING TO EJECT NORTHEAST...  
...INCREASINGLY NEGATIVE TILT EJECTING WAVE AND ASSOCIATED  
CYCLOGENESIS UP THE EAST COAST FRI-SAT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF / 00Z CMC  
CONFIDENCE: AVERAGE  
 
STRONG PV ANOMALY AT THE BASE OF THE CENTRAL US TROUGH WILL BEGIN  
TO EJECT NORTHEAST LATER TODAY AND TAKE ON AN INCREASINGLY  
NEGATIVE TILT. SURFACE CYCLOGENESIS SHOULD BECOME MORE PRONOUNCED  
AS THE WAVE APPROACHES THE SOUTHERN EXTENT OF THE APPALACHIANS ON  
FRIDAY...WITH MORE FOCUSED PRESSURE FALLS IN THE LEE OF THE  
MOUNTAINS OVER THE PIEDMONT REGION. ENSEMBLE SENSITIVITY ANALYSIS  
OF THE 00Z ECMWF ENSEMBLE SHOWED THAT THE MAJORITY OF REMAINING  
UNCERTAINTY BY DAY 2 (SATURDAY) IS RELATED TO NW-SE POSITIONAL  
VARIANCE OF THE LOW ALONG THE EVOLVING BAROCLINIC ZONE...OR IN  
OTHER WORDS HOW FAR INLAND THE SURFACE LOW TRACKS.  
 
MODELS HAVE SHOWN BETTER CLUSTERING OVERALL IN THE TRENDS OVER THE  
PAST SEVERAL MODEL CYCLES. HOWEVER...A FAIR AMOUNT OF SPREAD STILL  
EXISTS. THE 12Z NAM HAS A WEAKER SURFACE LOW AND AFTER 13/12Z  
(SATURDAY MORNING) BEGINS TO ACCELERATE THE LOW TO THE NORTHEAST  
MUCH FASTER THAN OTHER MODELS. THIS IS WELL AHEAD OF ENSEMBLE  
MEANS...INCLUDING THE 09Z SREF MEAN. THE NAM (AND TO A LESSER  
EXTENT THE 00Z UKMET) ALSO HAS ONE OF THE COLDER LOW-MID LEVEL  
TEMPERATURE PROFILES OVER THE NORTHEAST EVEN IN THE FACE OF STRONG  
WARM AIR ADVECTION. BECAUSE OF THESE CHARACTERISTICS...THE 12Z NAM  
IS EXCLUDED FROM THE PREFERENCE FOR THIS SYSTEM.  
 
THE 00Z UKMET HAS A SURFACE LOW TRACK FROM 12/06Z (EARLY FRIDAY  
MORNING) TO 13/12Z (SATURDAY MORNING) THAT IS TO THE NORTH AND  
SLOWER THAN OTHER AVAILABLE MODELS...ALTHOUGH IT IS NOT FAR OFF  
THE OVERALL CLUSTERING OF SURFACE LOW POSITIONS. HOWEVER...IT IS  
ALSO SLOWER THAN THE TROUGH ALOFT...AND GENERALLY IS IN LARGER  
CONTRAST IN THAT REGARD. THEREFORE...THE 00Z UKMET IS ALSO  
EXCLUDED FROM THE PREFERENCE AT THIS TIME.  
 
THE REMAINING MODELS...THE GFS...ECMWF...AND CMC...ARE QUITE  
SIMILAR TO THE 06Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN AND SHOW  
SMALLER DIFFERENCES OVERALL. THE 00Z ECMWF CONTINUES TO BE  
STRONGEST WITH THE SURFACE LOW...WHICH YIELDS A SLIGHTLY SLOWER  
PROGRESSION OVERALL. HOWEVER...AN EXAMINATION OF ECMWF ENSEMBLE  
MEMBERS SHOWS A CONSIDERABLE NUMBER THAT HAVE A SIMILAR SURFACE  
LOW INTENSITY AND A TRACK THAT IS EITHER SLOWER OR SLIGHTLY INLAND  
OF THE ENSEMBLE MEAN. THEREFORE...THE OPERATIONAL ECMWF IS  
INCLUDED IN THE PREFERENCE...AND A BLEND THAT INCORPORATES A FAIR  
AMOUNT OF THE ECMWF IS ALSO PREFERRED.  
 
...BROAD INITIAL TROUGH OVER FLORIDA DEAMPLIFYING WITH THE  
APPROACH OF STRONGER HEIGHT FALLS FROM THE WEST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
MODELS SHOW GOOD SIMILARITY WITH THIS TROUGH AS IT BECOMES  
ABSORBED BY THE APPROACHING TROUGH FROM THE WEST. THEREFORE...A  
GENERAL MODEL BLEND IS PREFERRED AT THIS TIME.  
 
   
..SHORTWAVE ARRIVING IN THE PACIFIC NORTHWEST TODAY
 
   
..DEAMPLIFYING OVER THE NRN/CTRL ROCKIES ON FRIDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-CMC BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
MODELS ARE TIGHTLY CLUSTERED WITH THIS SYSTEM AS IT ARRIVES IN THE  
PACIFIC NORTHWEST TODAY AND THEN QUICKLY DEAMPLIFIES IN THE  
NORTHWESTERLY FLOW ON THE BACKSIDE OF THE LARGE SCALE TROUGH. IN  
GENERAL THEY ARE ALSO VERY CLOSE WITH THE TEMPERATURE PROFILES  
ALSO...BUT THE CMC DOES LINGER COLDER AIR OVER MUCH OF THE REGION  
THAN OTHER MODELS. THEREFORE...THE 00Z CMC IS EXCLUDED FROM THE  
PREFERENCE BUT THERE IS ENOUGH SIMILARITY FROM THE OTHER MODELS  
FOR A GENERAL BLEND OTHERWISE.  
 
...SHORTWAVE DIVING SOUTH FROM THE CANADIAN ARCTIC TO THE NORTHERN  
PLAINS BY LATE SUNDAY...   
..ACCOMPANYING COLD FRONT PUSHING INTO THE NORTHERN CONUS
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 00Z ECMWF / 00Z CMC  
CONFIDENCE: AVERAGE  
 
THERE IS GOOD AGREEMENT THAT A SHORTWAVE ABOVE THE ARCTIC CIRCLE  
WILL DROP SOUTH AND PUSH INTO THE NORTHERN TIER OF STATES THIS  
WEEKEND. THE GFS...ECMWF...AND CMC ALL SHOW A SIMILAR STRUCTURE  
AND POSITION OF THE WAVE...DESPITE SOME DETAIL DIFFERENCES. THE  
00Z UKMET HAS A SHARPER WAVE AND SOME SLIGHT DOWNSTREAM RIDGING  
EMBEDDED WITHIN THE LARGER TROUGH DOES AFFECT THE ORIENTATION OF  
THE VORT MAX AND THE POSITION AND STRENGTH OF THE ASSOCIATED  
SURFACE FRONT AND SURFACE LOW. THE 12Z NAM HAS THE POSITION OF THE  
TROUGH FURTHER NORTHEAST AND APPEARS TO RESTRICT ITS AMPLITUDE  
MORE THAN OTHER MODELS BASED ON THE WESTERN CONUS RIDGE. FOR THESE  
REASONS...PREFER THE BETTER AGREEMENT OFFERED BY A BLEND OF THE  
GFS...ECMWF...AND CMC.  
 
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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