656  
FXUS10 KWNH 251655  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1154 AM EST THU JAN 25 2018  
 
VALID JAN 25/1200 UTC THRU JAN 29/0000 UTC  
 
..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...MID-LEVEL SHORTWAVE WEAKENING NORTHEASTWARD FROM WEST TEXAS  
TODAY/TONIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
   
..LARGE UPPER TROUGH MOVING THROUGH THE WESTERN U.S. TODAY
 
 
...SURFACE LOW NEAR THE U.S./CANADIAN BORDER MOVING EAST WITH  
TRAILING COLD FRONT FRIDAY THROUGH THE WEEKEND...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM / 00Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
THE 12Z GFS CONTINUES TO APPEAR FASTER THAN THE MODEL CONSENSUS  
WITH THE PROGRESSION OF THE 500 MB TROUGH MOVING ACROSS THE UPPER  
MISSISSIPPI VALLEY EARLY SATURDAY MORNING AND WITH ENERGY IN THE  
BASE OF THE TROUGH NEAR KANSAS AND MISSOURI. GIVEN THE 00Z UKMET  
HAS AN UNFAVORABLE INTERACTION OF VORTICITY CENTERS FRIDAY NIGHT  
LEADING TO A SLOWER PROGRESSION OF THE TROUGH DOWNSTREAM, WITH  
ENSEMBLE SPAGHETTI PLOTS SUPPORTING A NON 00Z UKMET BLEND ACROSS  
THE NORTH-CENTRAL U.S., A 12Z NAM/00Z ECMWF BLEND APPEARS MOST  
FAVORABLE WITH THIS SYSTEM.  
 
THIS PREFERENCE ALSO APPLIES ACROSS THE GULF COAST WHERE THE 12Z  
GFS IS LESS AGGRESSIVE MOISTURE RETURN INTO THE CENTRAL GULF COAST  
REGION ON SATURDAY. A FRONTAL WAVE IN THE GULF OF MEXICO APPEARS  
TO BE REPRESENTED IN THE DETERMINISTIC GUIDANCE BY SUNDAY MORNING.  
HOWEVER, THE 12Z GFS IS FASTER WITH THIS FEATURE AND IS STRONGER  
THAN THE REMAINING DETERMINISTIC GUIDANCE AND ONLY WEAKLY  
SUPPORTED IN THE ENSEMBLE DATA. THEREFORE, A 12Z NAM/00Z ECMWF  
BLEND APPEARS A BETTER FIT FOR THIS ENTIRE SYSTEM, FROM CANADA TO  
THE GULF COAST.  
 
...LOW AMPLITUDE MID-LEVEL SHORTWAVE NEARING THE PACIFIC NORTHWEST  
LATE FRIDAY NIGHT WITH ACCOMPANYING SURFACE LOW...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ENSEMBLE SCATTER LOW PLOTS SUPPORT A 12Z GFS...00Z ECMWF...00Z CMC  
BLEND WITH THE SURFACE LOW AS IT APPROACHES THE PACIFIC NORTHWEST.  
THERE IS MODERATELY GOOD AGREEMENT IN THE ENSEMBLE DATA TO SUPPORT  
THIS PREFERENCE. THE 12Z NAM IS FARTHER SOUTH WHILE THE 00Z UKMET  
IS STRONGER AND NORTHWARD.  
 
   
..LARGE CLOSED LOW APPROACHING BRITISH COLUMBIA LATE SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z UKMET BLEND  
CONFIDENCE: AVERAGE  
 
ENSEMBLE DATA IS REASONABLY CLUSTERED WITH THIS NEXT SYSTEM TO  
IMPACT THE WEST COAST, BUT THE 00Z UKMET APPEARS A LOW PROBABILITY  
SOLUTION GIVEN ITS PLACEMENT ON THE SLOW EDGE OF GEFS/ECMWF/CMC  
ENSEMBLE MEMBERS. CONFIDENCE IS ONLY AVERAGE CONSIDERING THE  
LONGER, 84 HOUR FORECAST RANGE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 
 

 
 
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