Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
150 PM 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 final preferences
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...Mid-level shortwave weakening northeastward from the southern
plains today... 
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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... 
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Preference: 12Z NAM/GFS/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.  Given good run to run consistency by the Canadian,
it 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... 
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Preference: 12Z GFS/ECMWF blend 
Confidence: Slightly above average 
 
Ensemble scatter low plots still support a 12Z GFS/ECMWF blend
with the surface low as it...and the associated mid level
wave...approaches the Pacific Northwest and then heads towards the
southeast.  The UKMET also offered a viable solution...primarily
on day 1.  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 it had a stronger vorticity
center by the time the vort reached the mean long wave position. 
For the remaining models, the latitudinal differences were pretty
small but increase late on day 3 when the NAM and UKMET became
slow/deep outlier compared with other model runs.
 
 
...Large closed low approaching British Columbia late Sunday... 
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Preference: Non UKMET 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.  Given the adjustments made by the 12Z Canadian...think
that the Canadian can once again be incorporated into the model
blend.  That leaves the 12Z UKMET as 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.   

Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml  
500 MB forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml  

Bann