196  
FXUS10 KWNH 261635  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1134 AM EST FRI JAN 26 2018  
 
VALID JAN 26/1200 UTC THRU JAN 30/0000 UTC  
 
..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION ALONG WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...MID-LEVEL SHORTWAVE WEAKENING NORTHEASTWARD FROM THE SOUTHERN  
PLAINS TODAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS HANDLE THE SYSTEM SIMILARLY AS IT MOVES EAST AND  
WEAKENS WITH TIME.  
 
   
..LARGE UPPER TROUGH MOVING THROUGH THE WESTERN/CENTRAL U.S
 
 
...SURFACE LOW NEAR THE U.S./CANADIAN BORDER MOVING EAST WITH  
TRAILING COLD FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: 12Z NAM/GFS...26/00Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE 12Z RUNS OF THE NCEP GUIDANCE HAVE ADJUSTED TOWARDS A  
CONSENSUS SOLUTION SUGGESTED BY THE OVERNIGHT ENSEMBLES AND THEY  
CLUSTERED PRETTY WELL WITH OTHER OPERATIONAL RUNS. THE 26/00Z  
UKMET WAS ON THE FLATTER/FASTER SIDE OF THE GUIDANCE BUT IT WAS  
NOT NEARLY AS FAST/FLAT AS IT WAS ON ITS WEDNESDAY NIGHT/THURSDAY  
MORNING RUNS. THIS BETTER CLUSTERING LEFT THE 00Z CANADIAN A BIT  
OUT OF PHASE. FOR THE MOMENT, WILL REMOVE IT FROM THE PREFERENCE  
PENDING ARRIVAL OF THE 12Z GUIDANCE.  
 
 
...LOW AMPLITUDE MID-LEVEL SHORTWAVE NEARING THE PACIFIC NORTHWEST  
 
LATE TONIGHT WITH ACCOMPANYING SURFACE LOW...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: 12Z GFS AND 26/00Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
ENSEMBLE SCATTER LOW PLOTS STILL SUPPORT A 12Z GFS AND 26/00Z  
ECMWF/UKMET BLEND WITH THE SURFACE LOW AS IT...AND THE ASSOCIATED  
MID LEVEL WAVE...APPROACHES THE PACIFIC NORTHWEST AND THEN HEADS  
TOWARDS THE SOUTHEAST. THE 12Z NAM WAS NOT QUITE AS FAR SOUTH  
WITH THE WAVE AS IT HAD BEEN IN PREVIOUS RUNS...BUT IT WAS STILL  
ON THE SOUTH SIDE OF THE ENVELOPE OF SOLUTIONS AND HAD A STRONGER  
VORTICITY CENTER. THE NAM HAS CONSISTENTLY BEEN ON THE STRONGER  
AND MORE SOUTHERLY SIDE OF THE GUIDANCE AS THE WAVE DROPS INTO THE  
MEAN LONG WAVE TROUGH. FOR THE MOST PART, THE LATITUDINAL  
DIFFERENCES ARE PRETTY SMALL BUT INCREASE LATE ON DAY 3 WHEN THE  
NAM BECAME SLOW/DEEP OUTLIER COMPARED WITH OTHER MODEL RUNS.  
 
   
..LARGE CLOSED LOW APPROACHING BRITISH COLUMBIA LATE SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: NON UKMET/CANADIAN MODEL BLEND  
CONFIDENCE: AVERAGE  
 
THE 26/00Z CANADIAN DEVELOPED A DOUBLE-BARRELED LOOK TO ITS  
MID/UPPER LEVEL SYSTEM CENTERED AROUND 145W...WHICH LED TO SEVERAL  
PERIODS WHERE THE CANADIAN WAS SOME 200 NMI NORTH OF OTHER MODEL  
GUIDANCE. THE 26/00Z UKMET APPEARED TO BE AN OUTLIER WITH THIS  
SYSTEM. OTHERWISE...THE REMAINING OPERATIONAL MODEL RUNS TENDED  
TO CLUSTER FAIRLY TIGHTLY WITH THE ENSEMBLE MEANS FROM THE GEFS  
AND ECMWF. DESPITE SOME RUN TO RUN ADJUSTMENTS, THE 12Z NCEP RUNS  
AND THE 26/00Z ECMWF STILL FORMED A REASONABLY GOOD CONSENSUS  
SOLUTION.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
 

 
 
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